I have a mid-80's HK integrated amp (PM-650). It's been very reliable and
sounds good, but there are a few things that have been bugging me:

1. The output of L & R channels are not equal... the left channel is louder
for any given source. It's in the pre-amp section, because I can make the
right speaker louder by flipping to "reverse stereo" so it's not the power
amp. I've aligned/calibrated the amp using the adjustments in the service
manual.

2. The balance knob is scratchy.

3. Every once in awhile one or both speakers cuts out. I have to toggle
the subsonic filter switch a few times to get it back on.

Anyway, last night I decided to give the amp a throrough cleaning, and I
replaced all of the electrolytic caps upstream of the reverse stereo switch.
I liberally sprayed all of the knobs (bass/treble/balance/tape monitor
select/volume) with MG contact cleaner and operated the knobs vigorously for
a minute or two. I then let the amp sit for an hour. The contact cleaner
evaporates almost instantaneously so I figured an hour was a reasonable time
to wait for the switches to dry out. When I powered up the amp everything
looked normal i.e. it lit up, but when I switched the speakers on (volume
all the way down), WHOA! CRACKLY STATIC, LOUD! None of the preamp controls
have any effect on the volume of static except my old nemesis, the subsonic
filter which creates a hum in the right channel when switched on. Switched
it back off, waited for four more hours. Double-checked all the solder
joints on the caps I had replaced for solder bridges, bad joints, correct
orientation on polar caps, etc.

When I fired it up this time, much much less static, but a) definitely some
residual low-level static on the right channel and b) left channel keeps
cutting out... need to crank up the volume and it "pops" back on. Sounds
good when it's on, and both channels very clear at high volume. Could be
worse I suppose.

My question is: how long does it take for this stuff to dry out? Could I
have just moved the dirt around inside the pots and made it worse? Should I
clean everything again?

I seem to have transformed a infrequent mild annoyance into a show-stopper.

Any replies greatly appreciated.

Dave

"Dave" wrote in message
news:n6KZh.19757$_G.10243@edtnps89...
I have a mid-80's HK integrated amp (PM-650). It's been very reliable and
sounds good, but there are a few things that have been bugging me:

1. The output of L & R channels are not equal... the left channel is louder
for any given source. It's in the pre-amp section, because I can make the
right speaker louder by flipping to "reverse stereo" so it's not the power
amp. I've aligned/calibrated the amp using the adjustments in the service
manual.

2. The balance knob is scratchy.

3. Every once in awhile one or both speakers cuts out. I have to toggle the
subsonic filter switch a few times to get it back on.

Anyway, last night I decided to give the amp a throrough cleaning, and I
replaced all of the electrolytic caps upstream of the reverse stereo switch. I
liberally sprayed all of the knobs (bass/treble/balance/tape monitor
select/volume) with MG contact cleaner and operated the knobs vigorously for a
minute or two. I then let the amp sit for an hour. The contact cleaner
evaporates almost instantaneously so I figured an hour was a reasonable time
to wait for the switches to dry out. When I powered up the amp everything
looked normal i.e. it lit up, but when I switched the speakers on (volume all
the way down), WHOA! CRACKLY STATIC, LOUD! None of the preamp controls have
any effect on the volume of static except my old nemesis, the subsonic filter
which creates a hum in the right channel when switched on. Switched it back
off, waited for four more hours. Double-checked all the solder joints on the
caps I had replaced for solder bridges, bad joints, correct orientation on
polar caps, etc.

When I fired it up this time, much much less static, but a) definitely some
residual low-level static on the right channel and b) left channel keeps
cutting out... need to crank up the volume and it "pops" back on. Sounds good
when it's on, and both channels very clear at high volume. Could be worse I
suppose.

My question is: how long does it take for this stuff to dry out? Could I
have just moved the dirt around inside the pots and made it worse? Should I
clean everything again?

I seem to have transformed a infrequent mild annoyance into a show-stopper.

Any replies greatly appreciated.

Dave


Since, by your own observations, the subsonic filter switch could be the
problem, or something in the immediate vicinity of the switch. What kind of
switch is it (slide switch, toggle switch, rotary switch)? If you can easily
disassemble it to get at the contacts, you might find that they are very
tarnished or even corroded; caused by airborne contaminants.
Also sounds like the volume pots are still dirty. Use a cleaner that lubricates
as well as cleans. A tip... when you spray the cleaner into the pot, turn the
set so that the residual cleaner can drain back out. That allows the cleaner to
float out any contaminants as it drains.
I have also found transistors to cause that exact problem. I surmise that the
wire bond from the external leads to the silicon inside breaks and becomes
extremely intermittent, and can be very difficult to find if you aren't wary of
this kind of fault. Lightly tap on each semiconductor in the area and see if
the audio is affected.
Actually, just about all types of components can become intermittent
(microphonic) in this manner, so using an insulated tool such as a plastic or
nylon tuning wand, tap components and circuit board to see if that affects the
audio.

Good luck...

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer to the end, the faster it goes.

"DaveM" wrote in message
. ..

Since, by your own observations, the subsonic filter switch could be the
problem, or something in the immediate vicinity of the switch. What kind
of switch is it (slide switch, toggle switch, rotary switch)? If you can
easily disassemble it to get at the contacts, you might find that they are
very tarnished or even corroded; caused by airborne contaminants.

It's a plastic push-button PCB-mounted switch, not easy to disassemble at
all. I'd worry about breaking the plastic parts which are, I'm sure, quite
irreplaceable. Not particularly accessible either as there is a display
controller board above the tone control board where the switch is located.

Also sounds like the volume pots are still dirty. Use a cleaner that
lubricates as well as cleans. A tip... when you spray the cleaner into
the pot, turn the set so that the residual cleaner can drain back out.
That allows the cleaner to float out any contaminants as it drains.

I was using zero residue cleaner, I'll pick up some lubricating contact
cleaner and give it another go. There appears to be a hole in the back of
each pot where you can see the shaft turn, plus a small (1-1.5mm) hole on
one side. Maybe a blast of compressed air after cleaning wouldn't hurt
either...

I have also found transistors to cause that exact problem. I surmise that
the wire bond from the external leads to the silicon inside breaks and
becomes extremely intermittent, and can be very difficult to find if you
aren't wary of this kind of fault. Lightly tap on each semiconductor in
the area and see if the audio is affected.
Actually, just about all types of components can become intermittent
(microphonic) in this manner, so using an insulated tool such as a plastic
or nylon tuning wand, tap components and circuit board to see if that
affects the audio.

This amp is totally discrete and there are no soldered wire connections (all
wound) , so I think (hope) the fact that BOTH channels are messed up
indicates a simple dirty pot problem... I did check voltages at maybe a
dozen transistors, both left and right channel from PS through the pre-amp
and amp and they were all really close to expected at idle. I don't know if
+/- 1V is significant on a 43VDC rail or not... anyway there are quite a
few transistors but nothing unmanageable and as there are no proprietary,
obscure, or out of production IC's in this dog, whatever I did is completely
fixable. I just hope that it doesn't take me 30 or 40 hours to figure it
out.

I may try just bridging the "open" pair of contacts on the subsonic filter
switch with a jumper wire and see if that helps.

Thanks for your help

Dave


Good luck...

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters
in the address)

Life is like a roll of toilet paper; the closer to the end, the faster it
goes.

On 1 May, 18:49, "Dave" wrote:
"DaveM" wrote in message
. ..

Since, by your own observations, the subsonic filter switch could be the
problem, or something in the immediate vicinity of the switch. What kind
of switch is it (slide switch, toggle switch, rotary switch)? If you can
easily disassemble it to get at the contacts, you might find that they are
very tarnished or even corroded; caused by airborne contaminants.

It's a plastic push-button PCB-mounted switch, not easy to disassemble at
all. I'd worry about breaking the plastic parts which are, I'm sure, quite
irreplaceable. Not particularly accessible either as there is a display
controller board above the tone control board where the switch is located.

Also sounds like the volume pots are still dirty. Use a cleaner that
lubricates as well as cleans. A tip... when you spray the cleaner into
the pot, turn the set so that the residual cleaner can drain back out.
That allows the cleaner to float out any contaminants as it drains.

I was using zero residue cleaner, I'll pick up some lubricating contact
cleaner and give it another go. There appears to be a hole in the back of
each pot where you can see the shaft turn, plus a small (1-1.5mm) hole on
one side. Maybe a blast of compressed air after cleaning wouldn't hurt
either...

I have also found transistors to cause that exact problem. I surmise that
the wire bond from the external leads to the silicon inside breaks and
becomes extremely intermittent, and can be very difficult to find if you
aren't wary of this kind of fault. Lightly tap on each semiconductor in
the area and see if the audio is affected.
Actually, just about all types of components can become intermittent
(microphonic) in this manner, so using an insulated tool such as a plastic
or nylon tuning wand, tap components and circuit board to see if that
affects the audio.

This amp is totally discrete and there are no soldered wire connections (all
wound) , so I think (hope) the fact that BOTH channels are messed up
indicates a simple dirty pot problem... I did check voltages at maybe a
dozen transistors, both left and right channel from PS through the pre-amp
and amp and they were all really close to expected at idle. I don't know if
+/- 1V is significant on a 43VDC rail or not... anyway there are quite a
few transistors but nothing unmanageable and as there are no proprietary,
obscure, or out of production IC's in this dog, whatever I did is completely
fixable. I just hope that it doesn't take me 30 or 40 hours to figure it
out.

I may try just bridging the "open" pair of contacts on the subsonic filter
switch with a jumper wire and see if that helps.

Thanks for your help

Dave



Good luck...



The still bad switch probably needs disassembling & reassembling, or
else replacing the individual switch or switch block. Rows of
pushbutton things on PCBs were a standard design around for many years
in the 70s & 80s, so finding a replacement from some scrap item is
likely.

The pot is either still dirty, probably not, or else is worn out or
cracked, or possibly the rivet at the end of the track is loose.

Replacing the pot is most likely the solution, you've already cleaned
it. Is its an oddity, rivets can be squashed, and worn out tracks can
be painted, tho this would unbalance the volume L-R tracking,

Re the off balance, there are reasons amps have balance controls. If
yours has none you can fit a potential divider in the channel with the
higher output, and set it up and replace the covers. If youre lcky and
the amp has external connections between pre and power sections, you
can put what you want between those 2, such as a new volume & balance
control.


NT

On Tue, 01 May 2007 16:42:59 GMT, "Dave"
wrote:

I seem to have transformed a infrequent mild annoyance into a show-stopper.

Had the exact same problem once in a mixing panel (unbalanced audio,
one channel fading away and coming back, incidental cracle and pop
sounds - cleaning did not help)

turned out to be a leaky electrolyte. Found it by measuring biasses on
every transistor in sight. Tapping the cap did not reveal anything
though.

--
- René

wrote in message
ups.com...
On 1 May, 18:49, "Dave" wrote:

The still bad switch probably needs disassembling & reassembling, or
else replacing the individual switch or switch block. Rows of
pushbutton things on PCBs were a standard design around for many years
in the 70s & 80s, so finding a replacement from some scrap item is
likely.


I re-cleaned the volume pot with some lubricating cleaner and dried it out
with a hair dryer (on low heat setting). The crackling in the right channel
has now all but disappeared.

The left channel, however, will now work for about 10-30 seconds when the
amp is first powered up, then distorts rapidly over about 1-3 seconds and
cuts out completely after that.

The amp is set up as follows:

Input jacks -- input selector PCB -- volume knob/loudness PCB -- tone
control PCB -- power amp PCB.

I'm going to take out the input caps off the tone control and route the
signal directly from the volume knob to the power amp. That will at least
tell me if the problem is with the preamp or power amp. I'm pretty sure
it's going to be in the power amp, as the second-to-last component in the
pre-amp (tone control board) is the stereo/reverse stereo/mono switch. If
the problem was in the preamp prior to this point, changing this switch
should move the problem from one speaker to the other. Which it does not.
The only downstream component from the stereo/reverse stereo/mono switch is
the balance pot.

When I replaced the caps on the power amp, I cleaned the board with spray
cleaner. It was filthy, like 30 years of dust and grime. In retrospect, I
probably shouldn't have bothered, maybe the cold temperature of the spray
cracked off an internal lead in one of the transisotrs or something.

The last component in the amp is "speaker protector". This is a white
rectangular box about 1-1/4"L x 3/16"W x 1/2"H (approx, I'm not looking at
it right now.). I don't know how this works, but could it possibly be my
problem? Or should I be thinking transistors? I guess if I've got the
whole amp apart it wouldn't be such a big deal to measure bias currents on
both channels at idle... there are 14 transistors per channel including the
outputs.


Re the off balance, there are reasons amps have balance controls. If
yours has none you can fit a potential divider in the channel with the
higher output, and set it up and replace the covers. If youre lcky and
the amp has external connections between pre and power sections, you
can put what you want between those 2, such as a new volume & balance
control.

My amp is integrated, but fortunately is very simple to split as the
connection between pre-amp and amp is a three-conductor wire. I've been
meaning to do this for awhile, I've just purchased a sub with line inputs
and outputs... will have to cannibalize some piece of junk for a block of
RCA jacks.

All of my signal path connections are wire-wound, not soldered. Is there
some tool to do this if I wanted to stay true to design and wind the
connections on my pre-out/main-in connections? Is there any benefit to
doing it this way? I'm guessing there probably is as it looks like a fair
bit more work than just plonking a blob of solder on a ribbon cable lead.

Thanks for the help.

Dave



NT

On May 1, 12:42 pm, "Dave" wrote:
I have a mid-80's HK integrated amp (PM-650). It's been very reliable

snip

Any replies greatly appreciated.

In no particular order:

a) cleaning pots and switches is only the first step. You need to
provide some (slight) amount of lubrication afterwards. 100% volatile
cleaners can cause serious friction after the skunge is removed
rebuilding additional skunge almost instantly. The idea is to exercise
the pot only as long as the cleaner is wet, then stop, then re-
saturate to rinse out the residue. *AFTER* that, a wee spritz of
lubricating cleaner makes all go smoothly.

b) switches are even 'more so' as wear can happen in any of several
ways including breaking of tabs or contact springs, and additional
friction can cause failure. So, same process. Saturate, exercise for a
few cycles whilst saturated, rinse, lubricate.

c) Look for broken traces on the boards, look (still) for bad caps. Do
you test the new caps *before* you install them? I have found about
0.5% of new electrolytic caps are bad or sufficiently out of spec to
be problematic. "Badness" typically manifests as intermittents... and
your delay may be related. Or, one you did not replace for whatever
reason...

d) you may believe that the power-amp section is clean, but one thing
I have experienced that is quite peculiar but as I have seen it
twice, it cannot be all that rare... an input transistor on the power-
amp side has become sufficiently different from its other-channel mate
that similar-volume signals to it are quite different in output
volume. RARE, and the only way you will catch this is to remove the
questionable transistors and put them either on a scope or tester that
can determine their actual response.

e) lastly and I have seen this only once and it was A BEAR to find. A
perfectly fine looking 1/2 watt resistor in the signal path had
drifted to 3X its nominal value. How did I find it? Well, every other #
$%^&*( part checked out, so I started measuring resitance "cold"
across both channels and comparing the results component by component.
When I found a difference, I started lifting legs about that point.
And there it was.

Good luck with it.

Peter Wieck
Wyncote, PA

wrote in message
ups.com...
On May 1, 12:42 pm, "Dave" wrote:

a) cleaning pots and switches is only the first step. You need to
provide some (slight) amount of lubrication afterwards. 100% volatile
cleaners can cause serious friction after the skunge is removed
rebuilding additional skunge almost instantly. The idea is to exercise
the pot only as long as the cleaner is wet, then stop, then re-
saturate to rinse out the residue. *AFTER* that, a wee spritz of
lubricating cleaner makes all go smoothly.


I re-cleaned with a cleaner with lubricant last night.

b) switches are even 'more so' as wear can happen in any of several
ways including breaking of tabs or contact springs, and additional
friction can cause failure. So, same process. Saturate, exercise for a
few cycles whilst saturated, rinse, lubricate.

Did not re-do switches. I will though.



c) Look for broken traces on the boards, look (still) for bad caps. Do
you test the new caps *before* you install them? I have found about
0.5% of new electrolytic caps are bad or sufficiently out of spec to
be problematic. "Badness" typically manifests as intermittents... and
your delay may be related. Or, one you did not replace for whatever
reason...


I don't have an ESR meter. Is testing plain ol' capacitance any help? I'd
like to think it's a capacitor given that that's all I changed out.

d) you may believe that the power-amp section is clean, but one thing
I have experienced that is quite peculiar but as I have seen it
twice, it cannot be all that rare... an input transistor on the power-
amp side has become sufficiently different from its other-channel mate
that similar-volume signals to it are quite different in output
volume. RARE, and the only way you will catch this is to remove the
questionable transistors and put them either on a scope or tester that
can determine their actual response.


This was an overnight change, so unless the change was mechanically induced
(definitely not ruling that out) I wouldn't be inclined to look there
justyet.

The more I think about it the less likely a pre-amp problem seems... the
signal goes through primary amplification (a few transisitors) then through
tone controls, subsonic filter, high cut filter, balance control -- power
amp. I've got a switch to bypass the tone control, and switches to bypass
the filters, plus a switch to reverse the channels between pre-amp and amp.
None of these affect the amp output. If I've got a bad cap in the amp
stages and am getting a DC offset at my outputs, that MAY be engaging the
speaker protection. Or, I suppose, worst case scenario I've baked one of my
giant expensive output transistors. I am assuming the speaker protection
(being two leaded) is a polyswitch. The distorted sound for a second or so
prior to speaker cut-out might match a polyswitch tripping, I don't know as
I've only ever had amps with relay protection (or none) in the past. Do you
know offhand if polyswitches tend to fail? I suppose probably as much as
any other component exposed to variable voltage and current.

I'm going to bypass the preamp section. If I can confirm that the problem
is in the amp, I could a) check DC voltages at all transistors until I find
one that's off or b) start swapping electrolytic capacitors from channel to
channel. there are only four per channel in the amp section.

e) lastly and I have seen this only once and it was A BEAR to find. A
perfectly fine looking 1/2 watt resistor in the signal path had
drifted to 3X its nominal value. How did I find it? Well, every other #
$%^&*( part checked out, so I started measuring resitance "cold"
across both channels and comparing the results component by component.
When I found a difference, I started lifting legs about that point.
And there it was.


Yes I've had several of those; they can try your patience.

Good luck with it.


Thanks, I may just need it.

Peter Wieck
Wyncote, PA

Dave wrote:
wrote in message
ups.com...
On 1 May, 18:49, "Dave" wrote:

The still bad switch probably needs disassembling & reassembling, or
else replacing the individual switch or switch block. Rows of
pushbutton things on PCBs were a standard design around for many
years in the 70s & 80s, so finding a replacement from some scrap
item is likely.


I re-cleaned the volume pot with some lubricating cleaner and dried
it out with a hair dryer (on low heat setting). The crackling in the
right channel has now all but disappeared.

The left channel, however, will now work for about 10-30 seconds when
the amp is first powered up, then distorts rapidly over about 1-3
seconds and cuts out completely after that.

The amp is set up as follows:

Input jacks -- input selector PCB -- volume knob/loudness PCB --
tone control PCB -- power amp PCB.

I'm going to take out the input caps off the tone control and route
the signal directly from the volume knob to the power amp. That will
at least tell me if the problem is with the preamp or power amp. I'm
pretty sure it's going to be in the power amp, as the second-to-last
component in the pre-amp (tone control board) is the stereo/reverse
stereo/mono switch. If the problem was in the preamp prior to this
point, changing this switch should move the problem from one speaker
to the other. Which it does not. The only downstream component from
the stereo/reverse stereo/mono switch is the balance pot.

When I replaced the caps on the power amp, I cleaned the board with
spray cleaner. It was filthy, like 30 years of dust and grime. In
retrospect, I probably shouldn't have bothered, maybe the cold
temperature of the spray cracked off an internal lead in one of the
transisotrs or something.
The last component in the amp is "speaker protector". This is a white
rectangular box about 1-1/4"L x 3/16"W x 1/2"H (approx, I'm not
looking at it right now.). I don't know how this works, but could it
possibly be my problem? Or should I be thinking transistors? I
guess if I've got the whole amp apart it wouldn't be such a big deal
to measure bias currents on both channels at idle... there are 14
transistors per channel including the outputs.


Re the off balance, there are reasons amps have balance controls. If
yours has none you can fit a potential divider in the channel with
the higher output, and set it up and replace the covers. If youre
lcky and the amp has external connections between pre and power
sections, you can put what you want between those 2, such as a new
volume & balance control.

My amp is integrated, but fortunately is very simple to split as the
connection between pre-amp and amp is a three-conductor wire. I've
been meaning to do this for awhile, I've just purchased a sub with
line inputs and outputs... will have to cannibalize some piece of
junk for a block of RCA jacks.

All of my signal path connections are wire-wound, not soldered. Is
there some tool to do this if I wanted to stay true to design and
wind the connections on my pre-out/main-in connections? Is there any
benefit to doing it this way? I'm guessing there probably is as it
looks like a fair bit more work than just plonking a blob of solder
on a ribbon cable lead.
Thanks for the help.

Dave



NT

The posts I've seen in this thread do seem to suggest a problem with
coupling caps. Also, I've seen bad (open circuit or intermittent)
polystyrene caps on HK's in the past.

If you're not already using them, a sine/square generator and an
oscilloscope would be most useful here. In addition to rapidly narrowing
down to the affected stage, a square wave might show that you have a
frequency response problem in the affected stage. If so, the source of the
problem may well be more obvious.

Remember that with coupling caps, you can often get a clue with DC voltages.
There may be DC, or a higher DC than the other channel, on the output side
of a bad cap, or the following transistor stage may show a low collector
voltage.

If indeed the static was not controlled by the volume or balance, then your
problem is narrowed down a bit, assuming there is only the one problem
involved here

I have the service manual pdf if you need it.


Mark Z.

"Mark D. Zacharias" wrote in message
...

The posts I've seen in this thread do seem to suggest a problem with
coupling caps. Also, I've seen bad (open circuit or intermittent)
polystyrene caps on HK's in the past.

If you're not already using them, a sine/square generator and an
oscilloscope would be most useful here. In addition to rapidly narrowing
down to the affected stage, a square wave might show that you have a
frequency response problem in the affected stage. If so, the source of the
problem may well be more obvious.

Remember that with coupling caps, you can often get a clue with DC
voltages. There may be DC, or a higher DC than the other channel, on the
output side of a bad cap, or the following transistor stage may show a low
collector voltage.

If indeed the static was not controlled by the volume or balance, then
your problem is narrowed down a bit, assuming there is only the one
problem involved here

I have the service manual pdf if you need it.


Thanks Mark, I've got the service manual. I do not currently own a
functioning oscilloscope (two fine doorstops), yes it would certainly help
here. Ah, but these old amps are simple enough to diagnose without one.
Nothing but resistors, caps, and transistors. And time, lots and lots of
time.

The problem is definitely in the amp section. I separated the pre-amp and
amp and tested both. The pre-amp drove an external amp just fine, the amp
exhibited the same symptoms with another preamp.

As there are only four electrolytic caps in each channel of the amplifier,
it's a fairly quick fix to swap them out one at a time until (hopefully) the
amp comes back to life.

I tested the voltages everywhere in the amp on both channels, wherever
voltages were shown in the service manual. The affected (left) channel had
voltages a couple of volts higher ON AVERAGE (2-2.5VDC) than the
corresponding right channel components which were really close to expected
values. I replaced the input coupling cap on the bad channel which did not
help.

Following your advice I looked at collector voltages... there is one that
really stands out and that is Q405. Expected is -7.1V and I read -0.3V.
This collector is tied to the emitters of Q401 and Q403 via a resistor
network... the emitter voltages of Q401 and Q403 are also significantly off
(low). It's a tough call when your expected voltage is less than a volt...
Q401 emitter should be -0.6V and I see -0.2. Q403 should be -0.6 and I see
0. The only cap in the signal path prior to these transistors is C401, the
input coupling cap which I swapped out as a first try. Otherwise there's an
electrolytic from the negative rail to the base of Q405... that'll be next.

Thanks for your help.

Dave

On May 3, 10:38 am, "Dave" wrote:
"Mark D. Zacharias" wrote in igy.net...







The posts I've seen in this thread do seem to suggest a problem with
coupling caps. Also, I've seen bad (open circuit or intermittent)
polystyrene caps on HK's in the past.

If you're not already using them, a sine/square generator and an
oscilloscope would be most useful here. In addition to rapidly narrowing
down to the affected stage, a square wave might show that you have a
frequency response problem in the affected stage. If so, the source of the
problem may well be more obvious.

Remember that with coupling caps, you can often get a clue with DC
voltages. There may be DC, or a higher DC than the other channel, on the
output side of a bad cap, or the following transistor stage may show a low
collector voltage.

If indeed the static was not controlled by the volume or balance, then
your problem is narrowed down a bit, assuming there is only the one
problem involved here

I have the service manual pdf if you need it.

Thanks Mark, I've got the service manual. I do not currently own a
functioning oscilloscope (two fine doorstops), yes it would certainly help
here. Ah, but these old amps are simple enough to diagnose without one.
Nothing but resistors, caps, and transistors. And time, lots and lots of
time.

The problem is definitely in the amp section. I separated the pre-amp and
amp and tested both. The pre-amp drove an external amp just fine, the amp
exhibited the same symptoms with another preamp.

As there are only four electrolytic caps in each channel of the amplifier,
it's a fairly quick fix to swap them out one at a time until (hopefully) the
amp comes back to life.

I tested the voltages everywhere in the amp on both channels, wherever
voltages were shown in the service manual. The affected (left) channel had
voltages a couple of volts higher ON AVERAGE (2-2.5VDC) than the
corresponding right channel components which were really close to expected
values. I replaced the input coupling cap on the bad channel which did not
help.

Following your advice I looked at collector voltages... there is one that
really stands out and that is Q405. Expected is -7.1V and I read -0.3V.
This collector is tied to the emitters of Q401 and Q403 via a resistor
network... the emitter voltages of Q401 and Q403 are also significantly off
(low). It's a tough call when your expected voltage is less than a volt...
Q401 emitter should be -0.6V and I see -0.2. Q403 should be -0.6 and I see
0. The only cap in the signal path prior to these transistors is C401, the
input coupling cap which I swapped out as a first try. Otherwise there's an
electrolytic from the negative rail to the base of Q405... that'll be next.

Thanks for your help.

Dave- Hide quoted text -

- Show quoted text -

Do you have a good transistor checker? (one that does good/bad and is
also capable of matching?)

Where are you (by region)?

Peter Wieck
Wyncote, PA

wrote in message
oups.com...
On May 3, 10:38 am, "Dave" wrote:

Do you have a good transistor checker? (one that does good/bad and is
also capable of matching?)

Where are you (by region)?

Peter Wieck
Wyncote, PA

I've got a transistor checker on my multimeter, it shows an arbitrary hfe
which, for a given transistor, never matches what's in the data sheet. Of
course the gain in the datasheet is always at a particular voltage and
current and I'm not sure what voltages/currents are applied by the meter...
or whether the voltage or current is controlled at all. I'm guessing 9V at
whatever the multimeter battery can put out for current through an unknown
series resistor. If it's a truly fried transistor, no value is returned for
hfe. I've had as much luck testing transistors with an ohmmeter.

I've never really trusted it to be honest with you.

Are you thinking driver transistor? Maybe one early in the signal path
which could introduce DC voltage which carries right through and would
explain the elevated voltages I am seeing in the left channel?

I live in Penticton, British Columbia, Canada. It's about 250 miles inland
from Vancouver and about 40 miles from the Washington border. It's a town
of 30,000 and, as you may surmise, very little of my equipment and parts is
purchased locally.

Dave

On May 3, 2:32 pm, "Dave" wrote:
wrote in message

oups.com... On May 3, 10:38 am, "Dave" wrote:

Do you have a good transistor checker? (one that does good/bad and is
also capable of matching?)

Where are you (by region)?

Peter Wieck
Wyncote, PA

I've got a transistor checker on my multimeter, it shows an arbitrary hfe
which, for a given transistor, never matches what's in the data sheet. Of
course the gain in the datasheet is always at a particular voltage and
current and I'm not sure what voltages/currents are applied by the meter...
or whether the voltage or current is controlled at all. I'm guessing 9V at
whatever the multimeter battery can put out for current through an unknown
series resistor. If it's a truly fried transistor, no value is returned for
hfe. I've had as much luck testing transistors with an ohmmeter.

I've never really trusted it to be honest with you.

Are you thinking driver transistor? Maybe one early in the signal path
which could introduce DC voltage which carries right through and would
explain the elevated voltages I am seeing in the left channel?

I live in Penticton, British Columbia, Canada. It's about 250 miles inland
from Vancouver and about 40 miles from the Washington border. It's a town
of 30,000 and, as you may surmise, very little of my equipment and parts is
purchased locally.

Dave

Exactly on the driver transistor. And "by region" I was thinking if
you were relatively nearby I would send you my transistor checker to
help through this process. Canada may be squirrelly what with customs
and such, by the time it reached you, you would have found the
problem. Then you would have to send it back.

I have had very good luck "pairing" transistors when doing repairs/
upgrades for 70s vintage SS amps (Dynaco, Scott, AR, Fisher), that is
making sure the 'right-side' transistor is reasonably closely matched
to the same 'left-side' transistor. This little instrument really does
help.

http://cgi.ebay.com/Schlumberger-Hea...mZ170108095101

Not as fancy as their IT-30, but it does the trick

Peter Wieck
Wyncote, PA

wrote in message
ps.com...
I have had very good luck "pairing" transistors when doing repairs/
upgrades for 70s vintage SS amps (Dynaco, Scott, AR, Fisher), that is
making sure the 'right-side' transistor is reasonably closely matched
to the same 'left-side' transistor. This little instrument really does
help.

Thanks for the link. As luck would have it, the seller lives in my home
town of Camden, Maine. Weird.

This tool would be really really handy and it's a helluva' lot cheaper than
a 'scope.

A couple of the driver transistors are not available, 2SC2603 and 2SA949's.
NTE crosses would have to do.

Thanks

Dave

On May 3, 3:20 pm, "Dave" wrote:

A couple of the driver transistors are not available, 2SC2603 and 2SA949's.
NTE crosses would have to do.

Exactly.

And why I try to get a bit closer than a cross-reference when I use
even direct-replacements. Unlike tubes which can vary somewhat,
transistors can vary pretty vastly, well beyond what common sense
suggests. And even though transistors do not really have a "burn-in",
when they begin to fail they can drift for a brief period before final
failure sets in.

Peter Wieck
Wyncote, PA

On May 2, 6:39 pm, "Dave" wrote:
wrote in message

ups.com...

On May 1, 12:42 pm, "Dave" wrote:

a) cleaning pots and switches is only the first step. You need to
provide some (slight) amount of lubrication afterwards. 100% volatile
cleaners can cause serious friction after the skunge is removed
rebuilding additional skunge almost instantly. The idea is to exercise
the pot only as long as the cleaner is wet, then stop, then re-
saturate to rinse out the residue. *AFTER* that, a wee spritz of
lubricating cleaner makes all go smoothly.

I re-cleaned with a cleaner with lubricant last night.

b) switches are even 'more so' as wear can happen in any of several
ways including breaking of tabs or contact springs, and additional
friction can cause failure. So, same process. Saturate, exercise for a
few cycles whilst saturated, rinse, lubricate.

Did not re-do switches. I will though.



c) Look for broken traces on the boards, look (still) for bad caps. Do
you test the new caps *before* you install them? I have found about
0.5% of new electrolytic caps are bad or sufficiently out of spec to
be problematic. "Badness" typically manifests as intermittents... and
your delay may be related. Or, one you did not replace for whatever
reason...

I don't have an ESR meter. Is testing plain ol' capacitance any help? I'd
like to think it's a capacitor given that that's all I changed out.

d) you may believe that the power-amp section is clean, but one thing
I have experienced that is quite peculiar but as I have seen it
twice, it cannot be all that rare... an input transistor on the power-
amp side has become sufficiently different from its other-channel mate
that similar-volume signals to it are quite different in output
volume. RARE, and the only way you will catch this is to remove the
questionable transistors and put them either on a scope or tester that
can determine their actual response.

This was an overnight change, so unless the change was mechanically induced
(definitely not ruling that out) I wouldn't be inclined to look there
justyet.

The more I think about it the less likely a pre-amp problem seems... the
signal goes through primary amplification (a few transisitors) then through
tone controls, subsonic filter, high cut filter, balance control -- power
amp. I've got a switch to bypass the tone control, and switches to bypass
the filters, plus a switch to reverse the channels between pre-amp and amp.
None of these affect the amp output. If I've got a bad cap in the amp
stages and am getting a DC offset at my outputs, that MAY be engaging the
speaker protection. Or, I suppose, worst case scenario I've baked one of my
giant expensive output transistors. I am assuming the speaker protection
(being two leaded) is a polyswitch. The distorted sound for a second or so
prior to speaker cut-out might match a polyswitch tripping, I don't know as
I've only ever had amps with relay protection (or none) in the past. Do you
know offhand if polyswitches tend to fail? I suppose probably as much as
any other component exposed to variable voltage and current.

I'm going to bypass the preamp section. If I can confirm that the problem
is in the amp, I could a) check DC voltages at all transistors until I find
one that's off or b) start swapping electrolytic capacitors from channel to
channel. there are only four per channel in the amp section.

e) lastly and I have seen this only once and it was A BEAR to find. A
perfectly fine looking 1/2 watt resistor in the signal path had
drifted to 3X its nominal value. How did I find it? Well, every other #
$%^&*( part checked out, so I started measuring resitance "cold"
across both channels and comparing the results component by component.
When I found a difference, I started lifting legs about that point.
And there it was.

Yes I've had several of those; they can try your patience.

Good luck with it.

Thanks, I may just need it.

Peter Wieck
Wyncote, PA

There used to be a spray on the market - can't remember who made it at
the time, might have been GC - it was called "Blue Stuff". I worked
in a stereo service department thru college, and that spray was the
best we could find for cleaning stubbornly noisy pots and switches.
When you sprayed it on it formed a mildly abrasive blue paste, which
would actually scrub the tarnish and dirt off of switch contacts. I
never saw it fail, even with the noisiest, most tarnished switches and
controls. I think it has diatomaceous earth in it.

Anyway, I think TechSpray carries it - might be worth a try
(www.techspray.com)

Dave wrote:
wrote in message
ps.com...
I have had very good luck "pairing" transistors when doing repairs/
upgrades for 70s vintage SS amps (Dynaco, Scott, AR, Fisher), that is
making sure the 'right-side' transistor is reasonably closely matched
to the same 'left-side' transistor. This little instrument really
does help.

Thanks for the link. As luck would have it, the seller lives in my
home town of Camden, Maine. Weird.

This tool would be really really handy and it's a helluva' lot
cheaper than a 'scope.

A couple of the driver transistors are not available, 2SC2603 and
2SA949's. NTE crosses would have to do.

Thanks

Dave

Maybe not an issue, but the 2603 and the 949 are not a pair. The C2603 is a
really small signal type, even smaller than a TO-92 package, The A949 is
similar to a TO-92 but taller. Don't know the package designation. I think
it's complement is the 2SC2229. They are readily available. I get them from
Onkyo and B & D Enterprises. BTW if you register on BDent.com you can get
datasheets for these really easily.

I'll try to look over your troubleshooting results with the schem and post
back.


Mark Z.

wrote in message
ps.com...

http://cgi.ebay.com/Schlumberger-Hea...mZ170108095101

Not as fancy as their IT-30, but it does the trick

I just picked up an IT-27 on eBay for $9. Plus of course the obligatory
$10-15 shipping, I should have it within a week or so.

Dave wrote:
"Mark D. Zacharias" wrote in message
...

The posts I've seen in this thread do seem to suggest a problem with
coupling caps. Also, I've seen bad (open circuit or intermittent)
polystyrene caps on HK's in the past.

If you're not already using them, a sine/square generator and an
oscilloscope would be most useful here. In addition to rapidly
narrowing down to the affected stage, a square wave might show that
you have a frequency response problem in the affected stage. If so,
the source of the problem may well be more obvious.

Remember that with coupling caps, you can often get a clue with DC
voltages. There may be DC, or a higher DC than the other channel, on
the output side of a bad cap, or the following transistor stage may
show a low collector voltage.

If indeed the static was not controlled by the volume or balance,
then your problem is narrowed down a bit, assuming there is only the
one problem involved here

I have the service manual pdf if you need it.


Thanks Mark, I've got the service manual. I do not currently own a
functioning oscilloscope (two fine doorstops), yes it would certainly
help here. Ah, but these old amps are simple enough to diagnose
without one. Nothing but resistors, caps, and transistors. And time,
lots and lots of time.

The problem is definitely in the amp section. I separated the
pre-amp and amp and tested both. The pre-amp drove an external amp
just fine, the amp exhibited the same symptoms with another preamp.

As there are only four electrolytic caps in each channel of the
amplifier, it's a fairly quick fix to swap them out one at a time
until (hopefully) the amp comes back to life.

I tested the voltages everywhere in the amp on both channels, wherever
voltages were shown in the service manual. The affected (left)
channel had voltages a couple of volts higher ON AVERAGE (2-2.5VDC)
than the corresponding right channel components which were really
close to expected values. I replaced the input coupling cap on the
bad channel which did not help.

Following your advice I looked at collector voltages... there is one
that really stands out and that is Q405. Expected is -7.1V and I
read -0.3V. This collector is tied to the emitters of Q401 and Q403
via a resistor network... the emitter voltages of Q401 and Q403 are
also significantly off (low). It's a tough call when your expected
voltage is less than a volt... Q401 emitter should be -0.6V and I see
-0.2. Q403 should be -0.6 and I see 0. The only cap in the signal path
prior to these transistors is
C401, the input coupling cap which I swapped out as a first try. Otherwise
there's an electrolytic from the negative rail to the base
of Q405... that'll be next.
Thanks for your help.

Dave

Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's don't use
relays, so they mute the signal til the amp stabilizes. On this model it is
Q405 and Q406 respectively. The transistor could be bad, but I would be
especially concerned with D401, R405, C405, C407, and D403, which is a 15
volt zener.

Could just be solder connections relating to the above, but in any case you
need to see that Q405 turns off hard a few seconds after turn-on. The -12.5
or so volts at the base is critical.

Mark Z.

"Mark D. Zacharias" wrote in message
news
Dave wrote:
"Mark D. Zacharias" wrote in message
...


Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's don't use
relays, so they mute the signal til the amp stabilizes. On this model it
is Q405 and Q406 respectively. The transistor could be bad, but I would be
especially concerned with D401, R405, C405, C407, and D403, which is a 15
volt zener.

Could just be solder connections relating to the above, but in any case
you need to see that Q405 turns off hard a few seconds after turn-on.
The -12.5 or so volts at the base is critical.

Mark Z.

Mark:

First off, thanks very much for all of your insight and time.

Okay, as I had just "upgraded" C405 and C407, I put the originals back.
Left channel is now functional once again, although I haven't had time to
check my voltages yet nor have I given it a good listening test. I can't
say why, but I've got a gut feeling my voltages are still on the high side.
How common is it for zener voltages to wander over three decades?

I set about setting the idle currents and, as soon as I touched V404 (right
channel), poof, right channel gone. I think the 1K pot just disintegrated
when I moved it after 30 years of sitting in one position. Well, I must be
doing something right, because I stumbled across a 1K 70's style (BIG) pot
in one of my many doorstops which I am cannibalizing to make myself an ESR
meter. I'll put it in tonight, hopefully it's in better condition than the
one I'm taking out. One wonders at moments like this whether one is moving
forward or backward...

I can't believe there are so few companies that make ESR meters... the more
I get into electronics repair, the more critical such a piece of equipment
becomes. Ditto with a transistor tester although there seem to be tons of
those on the market.

I have a hard time with transistor theory... I understand what they do, but
get quite confused when I see a whole bunch of them tied together,
controlling each other with various feedback schemes. That's when I start
testing components as I lack the deductive skills required to narrow things
down, as you did, to a single transistor and associated passive components.
Hopefully I'll get better at it... I've read some texts but don't find the
ones I've read particularly helpful. They all seem to assume that one is in
a laboratory environemnt at school with access to and training on the SPICE
program, in particular. Which I do not have.

An oscilloscope and signal generator are handy, but again is somewhat hit or
miss (for me) when I get into a transistor network as it's not immediately
obvious where the signal path is. It's almost easier in a newer amp with
IC's... what you end up doing is replacing an IC with ten transistors in it
because you know the problems's gotta' be in there someplace if you've got
signal going in and none coming out. If the IC is not obsolete and/or
proprietary and hence unavailable. In the past I've used the scope to
localize distortion which saves A LOT of time and lifting of legs to test
components.

I am quickly learning that with vintage audio gear, if it ain't broke, don't
even breathe on it or else...

Thanks again for your help.

Dave

"Dave" wrote in
news:UZ%%h.30287$KN6.29376@edtnps89:

An oscilloscope and signal generator are handy, but again is somewhat
hit or miss (for me) when I get into a transistor network as it's not
immediately obvious where the signal path is. It's almost easier in a
newer amp with IC's... what you end up doing is replacing an IC with ten
transistors in it because you know the problems's gotta' be in there
someplace if you've got signal going in and none coming out. If the IC
is not obsolete and/or proprietary and hence unavailable. In the past
I've used the scope to localize distortion which saves A LOT of time and
lifting of legs to test components.


If you have a scope (it need not be an expensive one or have high freq
response) one of the handiest trouble shooting devices I have is a curve
tracer I built that is similar to this one:
http://www.techlib.com/electronics/curvetrace.html

Mine is like the single range model.

Anyway, I find it very useful for locating bad transistors and bad gates on
IC because the 'knee' gets rounded or is absent on bad junctions.

Often, you can test 'in circuit', but sometimes you will have to cut some
traces to isolate the junction from caps or resisitors that are in parallel
with it.

A little practice with one of these, and a few 'reference junctions' to
compare with the curves you see, and you may love your curve tracer too.

--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

bz wrote:
"Dave" wrote in
news:UZ%%h.30287$KN6.29376@edtnps89:

An oscilloscope and signal generator are handy, but again is somewhat
hit or miss (for me) when I get into a transistor network as it's not
immediately obvious where the signal path is. It's almost easier in
a newer amp with IC's... what you end up doing is replacing an IC
with ten transistors in it because you know the problems's gotta' be
in there someplace if you've got signal going in and none coming
out. If the IC is not obsolete and/or proprietary and hence
unavailable. In the past I've used the scope to localize distortion
which saves A LOT of time and lifting of legs to test components.


If you have a scope (it need not be an expensive one or have high freq
response) one of the handiest trouble shooting devices I have is a
curve tracer I built that is similar to this one:
http://www.techlib.com/electronics/curvetrace.html

Mine is like the single range model.

Anyway, I find it very useful for locating bad transistors and bad
gates on IC because the 'knee' gets rounded or is absent on bad
junctions.

Often, you can test 'in circuit', but sometimes you will have to cut
some traces to isolate the junction from caps or resisitors that are
in parallel with it.

A little practice with one of these, and a few 'reference junctions'
to compare with the curves you see, and you may love your curve
tracer too.


I use a very similar device and have for years. It was instrumental in
making me a halfway decent tech. Without having this available I might have
given up on being a tech and moved on to something else before I ever "got a
clue".

Once a person has learned how to use this thing it really speeds up the
process of doing quick checks on components in-circuit. A leaky transistor
junction becomes obvious. Open capacitor, no problem. You can even connect
it to a phototransistor and fire a remote at the transistor and observe it
turning on and off on your 'scope screen (though this doesn't tell how well
the device works in-circuit...)


Mark Z.

"Mark D. Zacharias" wrote in message
...
bz wrote:
"Dave" wrote in
news:UZ%%h.30287$KN6.29376@edtnps89:

An oscilloscope and signal generator are handy, but again is somewhat
hit or miss (for me) when I get into a transistor network as it's not
immediately obvious where the signal path is. It's almost easier in
a newer amp with IC's... what you end up doing is replacing an IC
with ten transistors in it because you know the problems's gotta' be
in there someplace if you've got signal going in and none coming
out. If the IC is not obsolete and/or proprietary and hence
unavailable. In the past I've used the scope to localize distortion
which saves A LOT of time and lifting of legs to test components.


If you have a scope (it need not be an expensive one or have high freq
response) one of the handiest trouble shooting devices I have is a
curve tracer I built that is similar to this one:
http://www.techlib.com/electronics/curvetrace.html

Mine is like the single range model.

Anyway, I find it very useful for locating bad transistors and bad
gates on IC because the 'knee' gets rounded or is absent on bad
junctions.

Often, you can test 'in circuit', but sometimes you will have to cut
some traces to isolate the junction from caps or resisitors that are
in parallel with it.

A little practice with one of these, and a few 'reference junctions'
to compare with the curves you see, and you may love your curve
tracer too.


I use a very similar device and have for years. It was instrumental in
making me a halfway decent tech. Without having this available I might
have given up on being a tech and moved on to something else before I ever
"got a clue".

Once a person has learned how to use this thing it really speeds up the
process of doing quick checks on components in-circuit. A leaky transistor
junction becomes obvious. Open capacitor, no problem. You can even connect
it to a phototransistor and fire a remote at the transistor and observe it
turning on and off on your 'scope screen (though this doesn't tell how
well the device works in-circuit...)


Mark Z.

I must say I am intrigued... sort of an all-in-one tester which costs less
than $5 to make. Doesn't get much better than that. What is the value or
the variable resistor ? 1K? 100K? Or would one use the guess and check
method for an acceptable output on the scope?

Dave

"Dave" wrote in
news:VZm0i.38249$KN6.1602@edtnps89:


"Mark D. Zacharias" wrote in message
...
bz wrote:
"Dave" wrote in
news:UZ%%h.30287$KN6.29376@edtnps89:

An oscilloscope and signal generator are handy, but again is somewhat
hit or miss (for me) when I get into a transistor network as it's not
immediately obvious where the signal path is. It's almost easier in
a newer amp with IC's... what you end up doing is replacing an IC
with ten transistors in it because you know the problems's gotta' be
in there someplace if you've got signal going in and none coming
out. If the IC is not obsolete and/or proprietary and hence
unavailable. In the past I've used the scope to localize distortion
which saves A LOT of time and lifting of legs to test components.


If you have a scope (it need not be an expensive one or have high freq
response) one of the handiest trouble shooting devices I have is a
curve tracer I built that is similar to this one:
http://www.techlib.com/electronics/curvetrace.html

Mine is like the single range model.

Anyway, I find it very useful for locating bad transistors and bad
gates on IC because the 'knee' gets rounded or is absent on bad
junctions.

Often, you can test 'in circuit', but sometimes you will have to cut
some traces to isolate the junction from caps or resisitors that are
in parallel with it.

A little practice with one of these, and a few 'reference junctions'
to compare with the curves you see, and you may love your curve
tracer too.


I use a very similar device and have for years. It was instrumental in
making me a halfway decent tech. Without having this available I might
have given up on being a tech and moved on to something else before I
ever "got a clue".

Once a person has learned how to use this thing it really speeds up the
process of doing quick checks on components in-circuit. A leaky
transistor junction becomes obvious. Open capacitor, no problem. You
can even connect it to a phototransistor and fire a remote at the
transistor and observe it turning on and off on your 'scope screen
(though this doesn't tell how well the device works in-circuit...)


Mark Z.

I must say I am intrigued... sort of an all-in-one tester which costs
less than $5 to make. Doesn't get much better than that. What is the
value or the variable resistor ? 1K? 100K? Or would one use the guess
and check method for an acceptable output on the scope?


Yep. You want to have a good horizontal deflection. Depends on the gain on
your horizontal input.

I built my into a wallwart, brought the scope leads for the resistors
directly out through some slits in the case. I just clip the probes from my
scope to the leads.

Glued a diode to the case to use as a reference.

Used a few feet of light duty speaker wire and a couple of E-Z Hook clips
for the circuit board test end.



--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

In article VZm0i.38249$KN6.1602@edtnps89, "Dave" wrote:

"Mark D. Zacharias" wrote in message
t...
bz wrote:
"Dave" wrote in
news:UZ%%h.30287$KN6.29376@edtnps89:

An oscilloscope and signal generator are handy, but again is somewhat
hit or miss (for me) when I get into a transistor network as it's not
immediately obvious where the signal path is. It's almost easier in
a newer amp with IC's... what you end up doing is replacing an IC
with ten transistors in it because you know the problems's gotta' be
in there someplace if you've got signal going in and none coming
out. If the IC is not obsolete and/or proprietary and hence
unavailable. In the past I've used the scope to localize distortion
which saves A LOT of time and lifting of legs to test components.


If you have a scope (it need not be an expensive one or have high freq
response) one of the handiest trouble shooting devices I have is a
curve tracer I built that is similar to this one:
http://www.techlib.com/electronics/curvetrace.html

Mine is like the single range model.

Anyway, I find it very useful for locating bad transistors and bad
gates on IC because the 'knee' gets rounded or is absent on bad
junctions.

Often, you can test 'in circuit', but sometimes you will have to cut
some traces to isolate the junction from caps or resisitors that are
in parallel with it.

A little practice with one of these, and a few 'reference junctions'
to compare with the curves you see, and you may love your curve
tracer too.


I use a very similar device and have for years. It was instrumental in
making me a halfway decent tech. Without having this available I might
have given up on being a tech and moved on to something else before I ever
"got a clue".

Once a person has learned how to use this thing it really speeds up the
process of doing quick checks on components in-circuit. A leaky transistor
junction becomes obvious. Open capacitor, no problem. You can even connect
it to a phototransistor and fire a remote at the transistor and observe it
turning on and off on your 'scope screen (though this doesn't tell how
well the device works in-circuit...)


Mark Z.

I must say I am intrigued... sort of an all-in-one tester which costs less
than $5 to make. Doesn't get much better than that. What is the value or
the variable resistor ? 1K? 100K? Or would one use the guess and check
method for an acceptable output on the scope?

Seems like some cheap scopes came with a component tester. probably about
the same. Reminded me I somehow aquired a commercial unit, so i am looking at it, never used it.
It has a 555 oscillator and some circuitry, but I don'r have a schematic. Can't find
it on the web but will look some more. i should use this usefull tool.

greg

"GregS" wrote in message
...
In article VZm0i.38249$KN6.1602@edtnps89, "Dave"
wrote:

Seems like some cheap scopes came with a component tester. probably about
the same. Reminded me I somehow aquired a commercial unit, so i am looking
at it, never used it.
It has a 555 oscillator and some circuitry, but I don'r have a schematic.
Can't find
it on the web but will look some more. i should use this usefull tool.

greg

If the circuit is anything like the one in the link bz posted, it's a few
resistors and a transformer, shouldn't be hard to figure out schematic.

"Mark D. Zacharias" wrote in message
news

Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's don't use
relays, so they mute the signal til the amp stabilizes. On this model it
is Q405 and Q406 respectively. The transistor could be bad, but I would be
especially concerned with D401, R405, C405, C407, and D403, which is a 15
volt zener.

Could just be solder connections relating to the above, but in any case
you need to see that Q405 turns off hard a few seconds after turn-on.
The -12.5 or so volts at the base is critical.

Mark Z.
Something is still failing in my amp. As I noted, I put the original caps
(C401, 403, 405, 407) back in and the problem went away. For awhile. It's
back... I measured voltages after the right channel had cut out.

The collector of Q407 was 0V. So was the collector and base of Q409, and
the base of Q413. Makes sense as they're all tied together. The collector
of Q405 was also 0V. the collectors of Q411 and Q413 were ALSO 0V. I noted
that although R437 tested fine, it looks like it's been run hot. As in it's
dark brown and you can't really read the color bands any more.

I don't understand how Q405 works as far as the turn-on delay, but if it
were bad could it be causing no voltage where I've indicated?

I tested the other, working channel and all voltages were correct.

Thanks

Dave

Dave wrote:
"Mark D. Zacharias" wrote in message
news

Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's
don't use relays, so they mute the signal til the amp stabilizes. On
this model it is Q405 and Q406 respectively. The transistor could be
bad, but I would be especially concerned with D401, R405, C405,
C407, and D403, which is a 15 volt zener.

Could just be solder connections relating to the above, but in any
case you need to see that Q405 turns off hard a few seconds after
turn-on. The -12.5 or so volts at the base is critical.

Mark Z.
Something is still failing in my amp. As I noted, I put the original
caps (C401, 403, 405, 407) back in and the problem went away. For
awhile. It's back... I measured voltages after the right channel
had cut out.
The collector of Q407 was 0V. So was the collector and base of Q409,
and the base of Q413. Makes sense as they're all tied together. The
collector of Q405 was also 0V. the collectors of Q411 and Q413 were
ALSO 0V. I noted that although R437 tested fine, it looks like it's
been run hot. As in it's dark brown and you can't really read the
color bands any more.
I don't understand how Q405 works as far as the turn-on delay, but if
it were bad could it be causing no voltage where I've indicated?

I tested the other, working channel and all voltages were correct.

Thanks

Dave

I need the base and emitter voltages on Q405 versus Q406. I wasn't thinking
clearly before, but the basic principle is the same. As the power supply
comes up, a positive voltage is passed through D401 and D402 to turn ON Q405
and Q406. In the case of Q405, you can see that there should be a negative
voltage at the emitter, and a somewhat LESS negative voltage at the base.
This turns ON the transistor and should pass a negative voltage through the
transistor, so that the negative 7 volts or so appears at the collector. If
there's no voltage at the collector of Q405, it's likely there is no
negative voltage at the emitter either. Possibly R429 or R429 are opening
up, or there could be bad solder connections on one or both of them.

Let me know what you find.

Mark Z.

"Mark D. Zacharias" wrote in message
t...
Dave wrote:
"Mark D. Zacharias" wrote in message
news

Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's
don't use relays, so they mute the signal til the amp stabilizes. On
this model it is Q405 and Q406 respectively. The transistor could be
bad, but I would be especially concerned with D401, R405, C405,
C407, and D403, which is a 15 volt zener.

Could just be solder connections relating to the above, but in any
case you need to see that Q405 turns off hard a few seconds after
turn-on. The -12.5 or so volts at the base is critical.

Mark Z.
Something is still failing in my amp. As I noted, I put the original
caps (C401, 403, 405, 407) back in and the problem went away. For
awhile. It's back... I measured voltages after the right channel
had cut out.
The collector of Q407 was 0V. So was the collector and base of Q409,
and the base of Q413. Makes sense as they're all tied together. The
collector of Q405 was also 0V. the collectors of Q411 and Q413 were
ALSO 0V. I noted that although R437 tested fine, it looks like it's
been run hot. As in it's dark brown and you can't really read the
color bands any more.
I don't understand how Q405 works as far as the turn-on delay, but if
it were bad could it be causing no voltage where I've indicated?

I tested the other, working channel and all voltages were correct.

Thanks

Dave

I need the base and emitter voltages on Q405 versus Q406. I wasn't
thinking clearly before, but the basic principle is the same. As the power
supply comes up, a positive voltage is passed through D401 and D402 to
turn ON Q405 and Q406. In the case of Q405, you can see that there should
be a negative voltage at the emitter, and a somewhat LESS negative voltage
at the base. This turns ON the transistor and should pass a negative
voltage through the transistor, so that the negative 7 volts or so appears
at the collector. If there's no voltage at the collector of Q405, it's
likely there is no negative voltage at the emitter either. Possibly R429
or R429 are opening up, or there could be bad solder connections on one or
both of them.

Let me know what you find.

Oops I guess I omitted information... had typed it then deleted it as
insignificant. I did test the negative power rail at R417 where the schemo
shows -14.2V. It was, I think around -14.9V. In the zone anyways which
would rule out R427 or R429 as culprits. If one of these had opened up
would I not likely see a positive voltage at the base of Q405?

Base Collector Emitter
Q405 -14.2 -0.4 -14.7
Q406 -12.7 -6.9 -13.5

As you can see the base vs. emitter of the two transistors has a comparable
delta... say a half-volt lower at the base which is what you'd expect I
think.

So, if I have the correct voltages at the base and emitter of Q405, but the
wrong collector voltage, I should be looking hard at Q405? I would think
that the -0.4V seen at the collector would be derived from the 2 x -0.6V
coming out of Q401 and Q403 attenuated by R413/R415/R483 with no
contribution from Q405.

Dave

Dave wrote:
"Mark D. Zacharias" wrote in message
t...
Dave wrote:
"Mark D. Zacharias" wrote in message
news
Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's
don't use relays, so they mute the signal til the amp stabilizes.
On this model it is Q405 and Q406 respectively. The transistor
could be bad, but I would be especially concerned with D401, R405,
C405, C407, and D403, which is a 15 volt zener.

Could just be solder connections relating to the above, but in any
case you need to see that Q405 turns off hard a few seconds after
turn-on. The -12.5 or so volts at the base is critical.

Mark Z.
Something is still failing in my amp. As I noted, I put the
original caps (C401, 403, 405, 407) back in and the problem went
away. For awhile. It's back... I measured voltages after the
right channel had cut out.
The collector of Q407 was 0V. So was the collector and base of
Q409, and the base of Q413. Makes sense as they're all tied
together. The collector of Q405 was also 0V. the collectors of
Q411 and Q413 were ALSO 0V. I noted that although R437 tested
fine, it looks like it's been run hot. As in it's dark brown and
you can't really read the color bands any more.
I don't understand how Q405 works as far as the turn-on delay, but
if it were bad could it be causing no voltage where I've indicated?

I tested the other, working channel and all voltages were correct.

Thanks

Dave

I need the base and emitter voltages on Q405 versus Q406. I wasn't
thinking clearly before, but the basic principle is the same. As the
power supply comes up, a positive voltage is passed through D401 and
D402 to turn ON Q405 and Q406. In the case of Q405, you can see that
there should be a negative voltage at the emitter, and a somewhat
LESS negative voltage at the base. This turns ON the transistor and
should pass a negative voltage through the transistor, so that the
negative 7 volts or so appears at the collector. If there's no
voltage at the collector of Q405, it's likely there is no negative
voltage at the emitter either. Possibly R429 or R429 are opening up,
or there could be bad solder connections on one or both of them.

Let me know what you find.

Oops I guess I omitted information... had typed it then deleted it as
insignificant. I did test the negative power rail at R417 where the
schemo shows -14.2V. It was, I think around -14.9V. In the zone
anyways which would rule out R427 or R429 as culprits. If one of
these had opened up would I not likely see a positive voltage at the
base of Q405?
Base Collector Emitter
Q405 -14.2 -0.4 -14.7
Q406 -12.7 -6.9 -13.5

As you can see the base vs. emitter of the two transistors has a
comparable delta... say a half-volt lower at the base which is what
you'd expect I think.

So, if I have the correct voltages at the base and emitter of Q405,
but the wrong collector voltage, I should be looking hard at Q405? I
would think that the -0.4V seen at the collector would be derived
from the 2 x -0.6V coming out of Q401 and Q403 attenuated by
R413/R415/R483 with no contribution from Q405.

Dave


I do think I'd replace Q405 at this point. You say the B-E voltage is
comparable but I don't think so. There's a big difference between 0.5 volts
and 0.8 volts when it comes to turning on a transistor. If the transistor
isn't the problem I'd still say it's not turning on sufficiently. Could be a
resistor is not open but the value has changed, for example.


Mark Z.

Mark Z.

"Mark D. Zacharias" wrote in message
.. .
Dave wrote:
"Mark D. Zacharias" wrote in message
t...
Dave wrote:
"Mark D. Zacharias" wrote in message
news
Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's
don't use relays, so they mute the signal til the amp stabilizes.
On this model it is Q405 and Q406 respectively. The transistor
could be bad, but I would be especially concerned with D401, R405,
C405, C407, and D403, which is a 15 volt zener.

Could just be solder connections relating to the above, but in any
case you need to see that Q405 turns off hard a few seconds after
turn-on. The -12.5 or so volts at the base is critical.

Mark Z.
Something is still failing in my amp. As I noted, I put the
original caps (C401, 403, 405, 407) back in and the problem went
away. For awhile. It's back... I measured voltages after the
right channel had cut out.
The collector of Q407 was 0V. So was the collector and base of
Q409, and the base of Q413. Makes sense as they're all tied
together. The collector of Q405 was also 0V. the collectors of
Q411 and Q413 were ALSO 0V. I noted that although R437 tested
fine, it looks like it's been run hot. As in it's dark brown and
you can't really read the color bands any more.
I don't understand how Q405 works as far as the turn-on delay, but
if it were bad could it be causing no voltage where I've indicated?

I tested the other, working channel and all voltages were correct.

Thanks

Dave

I need the base and emitter voltages on Q405 versus Q406. I wasn't
thinking clearly before, but the basic principle is the same. As the
power supply comes up, a positive voltage is passed through D401 and
D402 to turn ON Q405 and Q406. In the case of Q405, you can see that
there should be a negative voltage at the emitter, and a somewhat
LESS negative voltage at the base. This turns ON the transistor and
should pass a negative voltage through the transistor, so that the
negative 7 volts or so appears at the collector. If there's no
voltage at the collector of Q405, it's likely there is no negative
voltage at the emitter either. Possibly R429 or R429 are opening up,
or there could be bad solder connections on one or both of them.

Let me know what you find.

Oops I guess I omitted information... had typed it then deleted it as
insignificant. I did test the negative power rail at R417 where the
schemo shows -14.2V. It was, I think around -14.9V. In the zone
anyways which would rule out R427 or R429 as culprits. If one of
these had opened up would I not likely see a positive voltage at the
base of Q405?
Base Collector Emitter
Q405 -14.2 -0.4 -14.7
Q406 -12.7 -6.9 -13.5

As you can see the base vs. emitter of the two transistors has a
comparable delta... say a half-volt lower at the base which is what
you'd expect I think.

So, if I have the correct voltages at the base and emitter of Q405,
but the wrong collector voltage, I should be looking hard at Q405? I
would think that the -0.4V seen at the collector would be derived
from the 2 x -0.6V coming out of Q401 and Q403 attenuated by
R413/R415/R483 with no contribution from Q405.

Dave


I do think I'd replace Q405 at this point. You say the B-E voltage is
comparable but I don't think so. There's a big difference between 0.5
volts and 0.8 volts when it comes to turning on a transistor. If the
transistor isn't the problem I'd still say it's not turning on
sufficiently. Could be a resistor is not open but the value has changed,
for example.


Well, I'll lift the legs of R427 and R429... and, I suppose, R407, R417 and
R405 just to rule out the resistors as I likely have replacements kicking
around for them whereas the transistor will need to be procured. Something
has got to be causing the ~1.5V differential between the R and L amp
channels in the first place.

I could add a small ~40-ohm resistor to the base, too and see if Q405 turns
on with a 0.8V B-E drop... FYI the spec drop is only 0.6V and I doubt the
designer would cut it so close that a 0.1V difference causes failure... but
them I'm often surprised.

Will post results, might be awhile before I get my hands on the transistor.

Out of curiousity, what does the Q5/Q6 circuit which biases Q405 do? As
near as I can tell, it takes 30VAC prior to rectification, runs it through a
diode to separate out the negative half of the wave, then past a 12V zener
to drop the voltage. Not sure what the function of D9 is, it is oriented
the reverse of D8. you end up with -1.1V at the base of Q5. The net result
being -0.56V out of the collector of Q6 to bias Q405/6. Seems like a lot of
work to derive a half-volt of regulated power but I guess they wanted it
fully independent of the amp channel power rails.

Thanks again.

Dave

Dave wrote:
"Mark D. Zacharias" wrote in message
.. .
Dave wrote:
"Mark D. Zacharias" wrote in message
t...
Dave wrote:
"Mark D. Zacharias" wrote in message
news
Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's
don't use relays, so they mute the signal til the amp stabilizes.
On this model it is Q405 and Q406 respectively. The transistor
could be bad, but I would be especially concerned with D401,
R405, C405, C407, and D403, which is a 15 volt zener.

Could just be solder connections relating to the above, but in
any case you need to see that Q405 turns off hard a few seconds
after turn-on. The -12.5 or so volts at the base is critical.

Mark Z.
Something is still failing in my amp. As I noted, I put the
original caps (C401, 403, 405, 407) back in and the problem went
away. For awhile. It's back... I measured voltages after the
right channel had cut out.
The collector of Q407 was 0V. So was the collector and base of
Q409, and the base of Q413. Makes sense as they're all tied
together. The collector of Q405 was also 0V. the collectors of
Q411 and Q413 were ALSO 0V. I noted that although R437 tested
fine, it looks like it's been run hot. As in it's dark brown and
you can't really read the color bands any more.
I don't understand how Q405 works as far as the turn-on delay, but
if it were bad could it be causing no voltage where I've
indicated? I tested the other, working channel and all voltages were
correct.

Thanks

Dave

I need the base and emitter voltages on Q405 versus Q406. I wasn't
thinking clearly before, but the basic principle is the same. As
the power supply comes up, a positive voltage is passed through
D401 and D402 to turn ON Q405 and Q406. In the case of Q405, you
can see that there should be a negative voltage at the emitter,
and a somewhat LESS negative voltage at the base. This turns ON
the transistor and should pass a negative voltage through the
transistor, so that the negative 7 volts or so appears at the
collector. If there's no voltage at the collector of Q405, it's
likely there is no negative voltage at the emitter either.
Possibly R429 or R429 are opening up, or there could be bad solder
connections on one or both of them. Let me know what you find.

Oops I guess I omitted information... had typed it then deleted it
as insignificant. I did test the negative power rail at R417 where
the schemo shows -14.2V. It was, I think around -14.9V. In the
zone anyways which would rule out R427 or R429 as culprits. If one
of these had opened up would I not likely see a positive voltage at
the base of Q405?
Base Collector Emitter
Q405 -14.2 -0.4 -14.7
Q406 -12.7 -6.9 -13.5

As you can see the base vs. emitter of the two transistors has a
comparable delta... say a half-volt lower at the base which is what
you'd expect I think.

So, if I have the correct voltages at the base and emitter of Q405,
but the wrong collector voltage, I should be looking hard at Q405? I
would think that the -0.4V seen at the collector would be derived
from the 2 x -0.6V coming out of Q401 and Q403 attenuated by
R413/R415/R483 with no contribution from Q405.

Dave


I do think I'd replace Q405 at this point. You say the B-E voltage is
comparable but I don't think so. There's a big difference between 0.5
volts and 0.8 volts when it comes to turning on a transistor. If the
transistor isn't the problem I'd still say it's not turning on
sufficiently. Could be a resistor is not open but the value has
changed, for example.


Well, I'll lift the legs of R427 and R429... and, I suppose, R407,
R417 and R405 just to rule out the resistors as I likely have
replacements kicking around for them whereas the transistor will need
to be procured. Something has got to be causing the ~1.5V
differential between the R and L amp channels in the first place.

I could add a small ~40-ohm resistor to the base, too and see if Q405
turns on with a 0.8V B-E drop... FYI the spec drop is only 0.6V and I
doubt the designer would cut it so close that a 0.1V difference
causes failure... but them I'm often surprised.

Will post results, might be awhile before I get my hands on the
transistor.
Out of curiousity, what does the Q5/Q6 circuit which biases Q405 do? As
near as I can tell, it takes 30VAC prior to rectification, runs it
through a diode to separate out the negative half of the wave, then
past a 12V zener to drop the voltage. Not sure what the function of
D9 is, it is oriented the reverse of D8. you end up with -1.1V at
the base of Q5. The net result being -0.56V out of the collector of
Q6 to bias Q405/6. Seems like a lot of work to derive a half-volt of
regulated power but I guess they wanted it fully independent of the
amp channel power rails.
Thanks again.

Dave

The function of Q5 and 6 is just to provide a more positive bias to Q405
after a delay (mainly determined by R24 and C22), enabling the amp channel
to "un-mute". It neen't be actually "positive" just more positive than the
negative rail at the emitter 0f Q401. Diode D9 is a question mark to me
also, but I suspect that since the capacitor C21 is only 33uF then some
ripple would still be present, and the diode might then act similar to a
zener and clamp the voltage drop across R24. I have to admit that since I'm
no engineer I can lose it when trying to figure the theory aspects. I just
fix them when they break.

You can swap Q405 and Q406 and see if the problem moves to the other
channel. Resistor R417 (560 ohm) can be checked in circuit. R405, a 68K,
would probably need to be checked out-of-circuit. Experience tells me that
high-value resistors can change value or go open-circuit for no good reason.
Worth keeping in the back of your mind sometimes as you're troubleshooting
problems such as this.

Not sure how you would use a 40 ohm added to the base of Q405.... in series
with R405 (68K) would do nothing, and in parallel with the BE junction of
Q405 would just keep the transistor from ever turning on in this
application.

At this point I think R427 and 429 are probably OK, or you wouldn't see the
voltage at the emitter of Q405. Our problem seems to involve getting 405 to
turn on, which is to say, getting the base of Q405 a bit more positve (less
negative) than it is right now.


Mark Z.

"Mark D. Zacharias" wrote in message
. ..
Dave wrote:
You can swap Q405 and Q406 and see if the problem moves to the other
channel. Resistor R417 (560 ohm) can be checked in circuit. R405, a 68K,
would probably need to be checked out-of-circuit. Experience tells me that
high-value resistors can change value or go open-circuit for no good
reason. Worth keeping in the back of your mind sometimes as you're
troubleshooting problems such as this.

R417 and R418 both test around 560 in circuit

R405 and R406 both test 66k in circuit

I'll try swapping Q405 and Q406 and see if the problem follows the
transistor. I found them relatively close (4 hour drive) in stock, or I can
order them in to my local supplier and wait a couple of days/weeks to
receive. How many do you think I'd have to order to find a pair with DC
gain matched to within, say, 15%? The 2SC2603 crosses to NTE289, which is
available as NTE289AMP, a matched pair for use in amplifiers...

For sure Q405 is not turning on. I watched the output of Q406 and, about 5
seconds after turning power on, it goes from -0.4 to -7.1V. Q405 just stays
at -0.4V.

Dave

"Mark D. Zacharias" wrote in message
. ..
Not sure how you would use a 40 ohm added to the base of Q405.... in
series with R405 (68K) would do nothing, and in parallel with the BE
junction of Q405 would just keep the transistor from ever turning on in
this application.

I meant in series with R407 to drop another 0.2V at the base of Q405 to try
to get it to turn on.

Dave wrote:
"Mark D. Zacharias" wrote in message
. ..
Dave wrote:
You can swap Q405 and Q406 and see if the problem moves to the other
channel. Resistor R417 (560 ohm) can be checked in circuit. R405, a
68K, would probably need to be checked out-of-circuit. Experience
tells me that high-value resistors can change value or go
open-circuit for no good reason. Worth keeping in the back of your
mind sometimes as you're troubleshooting problems such as this.

R417 and R418 both test around 560 in circuit

R405 and R406 both test 66k in circuit

I'll try swapping Q405 and Q406 and see if the problem follows the
transistor. I found them relatively close (4 hour drive) in stock,
or I can order them in to my local supplier and wait a couple of
days/weeks to receive. How many do you think I'd have to order to
find a pair with DC gain matched to within, say, 15%? The 2SC2603
crosses to NTE289, which is available as NTE289AMP, a matched pair
for use in amplifiers...
For sure Q405 is not turning on. I watched the output of Q406 and,
about 5 seconds after turning power on, it goes from -0.4 to -7.1V. Q405
just stays at -0.4V.

Dave

If they are using a 2SC2603 then it is not critical. The 2603 is a pretty
standard signal transistor - nothing special. A 2SC945 would be fine, heck,
even a ECG / NTE 123AP. Just make sure the basing is correct. An American
type transistor will usually go EBC rather than ECB as viewed from the
front.

Mark Z.

Dave wrote:
"Mark D. Zacharias" wrote in message
. ..
Not sure how you would use a 40 ohm added to the base of Q405.... in
series with R405 (68K) would do nothing, and in parallel with the BE
junction of Q405 would just keep the transistor from ever turning on
in this application.

I meant in series with R407 to drop another 0.2V at the base of Q405
to try to get it to turn on.

Ah. I get it.

40 ohms wouldn't get it. I'd try maybe about 1 kOhm to about 2.2K.

Mark Z.

"Mark D. Zacharias" wrote in message
. ..
Dave wrote:
"Mark D. Zacharias" wrote in message
. ..
Not sure how you would use a 40 ohm added to the base of Q405.... in
series with R405 (68K) would do nothing, and in parallel with the BE
junction of Q405 would just keep the transistor from ever turning on
in this application.

I meant in series with R407 to drop another 0.2V at the base of Q405
to try to get it to turn on.

Ah. I get it.

40 ohms wouldn't get it. I'd try maybe about 1 kOhm to about 2.2K.

Mark Z.

I figured that if 3.6K dropped the negative rail voltage from -42.6 to -14.2
(through R427/R429) then that's about 125 ohms/V. 40 ohms ~= 1/3V.

"Mark D. Zacharias" wrote in message
. ..
Dave wrote:
"Mark D. Zacharias" wrote in message
. ..
Dave wrote:
You can swap Q405 and Q406 and see if the problem moves to the other
channel. Resistor R417 (560 ohm) can be checked in circuit. R405, a
68K, would probably need to be checked out-of-circuit. Experience
tells me that high-value resistors can change value or go
open-circuit for no good reason. Worth keeping in the back of your
mind sometimes as you're troubleshooting problems such as this.

R417 and R418 both test around 560 in circuit

R405 and R406 both test 66k in circuit

I'll try swapping Q405 and Q406 and see if the problem follows the
transistor. I found them relatively close (4 hour drive) in stock,
or I can order them in to my local supplier and wait a couple of
days/weeks to receive. How many do you think I'd have to order to
find a pair with DC gain matched to within, say, 15%? The 2SC2603
crosses to NTE289, which is available as NTE289AMP, a matched pair
for use in amplifiers...
For sure Q405 is not turning on. I watched the output of Q406 and,
about 5 seconds after turning power on, it goes from -0.4 to -7.1V. Q405
just stays at -0.4V.

Dave

If they are using a 2SC2603 then it is not critical. The 2603 is a pretty
standard signal transistor - nothing special. A 2SC945 would be fine,
heck, even a ECG / NTE 123AP. Just make sure the basing is correct. An
American type transistor will usually go EBC rather than ECB as viewed
from the front.


OK. I have lots of 2SC945's, they're in everything. But... I swapped Q405
and Q406 and the problem DID NOT follow the transistor.

I kept thinking about C405 and C407. If either one leaked, even a little
bit, that would throw off the base voltage of Q405, maybe enough to keep it
from turning on. So I threw in a new C405 and, voila, Q405 now shows -5.9V
at the collector. Great, I says to myself, I am so smart. (Note to self,
find new source for electrolytic caps, two bad ones out of 30 so far). Set
about checking other voltages in the channel, but HEY! what the ????
Something else is not right.

The voltages that were out we

Base Collector Emitter
Q409 +34.2 +34.2
Q411 +33.0
Q413 +33.9 +33.8
Q401 +0.2
Q403 +0.4

I didn't check the collector voltages of Q401/Q403, I'll do that next but...
I'd be surprised if they weren't +40.5 given that all the other positive
voltages check out.

The negative power rail is fine at -43.5V, and I am getting my -12.5 at the
base of Q405 so it's not the negative supply.

If Q409 fails to turn on, then that would make Q413 not turn on either.
There would be then be no negative voltage applied to the collector of Q411
to get down to the +1.1V we want to see. I'll check out R439.

I wouldn't have expected to see a positive voltage at the collector of
either Q409 OR Q413 given that they're basically connected to the negative
power rail through a small value resistor. Almost makes you think that if
R439 is open, R445 would be too.

But then we're back to my basic lack of understanding of how the transistor
works...

I think I'm learning something here.

Dave

"Dave" wrote in message
news:Vsj3i.36782$Xh3.2600@edtnps90...

"Mark D. Zacharias" wrote in message
. ..
Dave wrote:
"Mark D. Zacharias" wrote in message
. ..
Dave wrote:
You can swap Q405 and Q406 and see if the problem moves to the other
channel. Resistor R417 (560 ohm) can be checked in circuit. R405, a
68K, would probably need to be checked out-of-circuit. Experience
tells me that high-value resistors can change value or go
open-circuit for no good reason. Worth keeping in the back of your
mind sometimes as you're troubleshooting problems such as this.

R417 and R418 both test around 560 in circuit

R405 and R406 both test 66k in circuit

I'll try swapping Q405 and Q406 and see if the problem follows the
transistor. I found them relatively close (4 hour drive) in stock,
or I can order them in to my local supplier and wait a couple of
days/weeks to receive. How many do you think I'd have to order to
find a pair with DC gain matched to within, say, 15%? The 2SC2603
crosses to NTE289, which is available as NTE289AMP, a matched pair
for use in amplifiers...
For sure Q405 is not turning on. I watched the output of Q406 and,
about 5 seconds after turning power on, it goes from -0.4 to -7.1V. Q405
just stays at -0.4V.

Dave

If they are using a 2SC2603 then it is not critical. The 2603 is a pretty
standard signal transistor - nothing special. A 2SC945 would be fine,
heck, even a ECG / NTE 123AP. Just make sure the basing is correct. An
American type transistor will usually go EBC rather than ECB as viewed
from the front.


OK. I have lots of 2SC945's, they're in everything. But... I swapped
Q405 and Q406 and the problem DID NOT follow the transistor.

I kept thinking about C405 and C407. If either one leaked, even a little
bit, that would throw off the base voltage of Q405, maybe enough to keep
it from turning on. So I threw in a new C405 and, voila, Q405 now
shows -5.9V at the collector. Great, I says to myself, I am so smart.
(Note to self, find new source for electrolytic caps, two bad ones out of
30 so far). Set about checking other voltages in the channel, but HEY!
what the ???? Something else is not right.

The voltages that were out we

Base Collector Emitter
Q409 +34.2 +34.2
Q411 +33.0
Q413 +33.9 +33.8
Q401 +0.2
Q403 +0.4

I didn't check the collector voltages of Q401/Q403, I'll do that next
but... I'd be surprised if they weren't +40.5 given that all the other
positive voltages check out.

The negative power rail is fine at -43.5V, and I am getting my -12.5 at
the base of Q405 so it's not the negative supply.

If Q409 fails to turn on, then that would make Q413 not turn on either.
There would be then be no negative voltage applied to the collector of
Q411 to get down to the +1.1V we want to see. I'll check out R439.

I wouldn't have expected to see a positive voltage at the collector of
either Q409 OR Q413 given that they're basically connected to the negative
power rail through a small value resistor. Almost makes you think that if
R439 is open, R445 would be too.

But then we're back to my basic lack of understanding of how the
transistor works...

I think I'm learning something here.

Dave


My kids have a game which is a 4 x 4 grid of holes. At any given time,
there is a mouse poking out of one hole. One pounds the mouse into the hole
with a hammer and this forces another mouse out of another hole. Sort of
how I feel here... fix one thing and it appears to break another.

"Dave" wrote in message
news:Vsj3i.36782$Xh3.2600@edtnps90...

"Mark D. Zacharias" wrote in message
. ..
Dave wrote:
"Mark D. Zacharias" wrote in message
. ..
Dave wrote:
You can swap Q405 and Q406 and see if the problem moves to the other
channel. Resistor R417 (560 ohm) can be checked in circuit. R405, a
68K, would probably need to be checked out-of-circuit. Experience
tells me that high-value resistors can change value or go
open-circuit for no good reason. Worth keeping in the back of your
mind sometimes as you're troubleshooting problems such as this.

R417 and R418 both test around 560 in circuit

R405 and R406 both test 66k in circuit

I'll try swapping Q405 and Q406 and see if the problem follows the
transistor. I found them relatively close (4 hour drive) in stock,
or I can order them in to my local supplier and wait a couple of
days/weeks to receive. How many do you think I'd have to order to
find a pair with DC gain matched to within, say, 15%? The 2SC2603
crosses to NTE289, which is available as NTE289AMP, a matched pair
for use in amplifiers...
For sure Q405 is not turning on. I watched the output of Q406 and,
about 5 seconds after turning power on, it goes from -0.4 to -7.1V. Q405
just stays at -0.4V.

Dave

If they are using a 2SC2603 then it is not critical. The 2603 is a pretty
standard signal transistor - nothing special. A 2SC945 would be fine,
heck, even a ECG / NTE 123AP. Just make sure the basing is correct. An
American type transistor will usually go EBC rather than ECB as viewed
from the front.


OK. I have lots of 2SC945's, they're in everything. But... I swapped
Q405 and Q406 and the problem DID NOT follow the transistor.

I kept thinking about C405 and C407. If either one leaked, even a little
bit, that would throw off the base voltage of Q405, maybe enough to keep
it from turning on. So I threw in a new C405 and, voila, Q405 now
shows -5.9V at the collector. Great, I says to myself, I am so smart.
(Note to self, find new source for electrolytic caps, two bad ones out of
30 so far). Set about checking other voltages in the channel, but HEY!
what the ???? Something else is not right.

The voltages that were out we

Base Collector Emitter
Q409 +34.2 +34.2
Q411 +33.0
Q413 +33.9 +33.8
Q401 +0.2
Q403 +0.4

I didn't check the collector voltages of Q401/Q403, I'll do that next
but... I'd be surprised if they weren't +40.5 given that all the other
positive voltages check out.

The negative power rail is fine at -43.5V, and I am getting my -12.5 at
the base of Q405 so it's not the negative supply.

If Q409 fails to turn on, then that would make Q413 not turn on either.
There would be then be no negative voltage applied to the collector of
Q411 to get down to the +1.1V we want to see. I'll check out R439.

I wouldn't have expected to see a positive voltage at the collector of
either Q409 OR Q413 given that they're basically connected to the negative
power rail through a small value resistor. Almost makes you think that if
R439 is open, R445 would be too.

But then we're back to my basic lack of understanding of how the
transistor works...

I think I'm learning something here.

Dave


What would happen if C415 were open?