Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..

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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Friday, October 5, 2018 at 11:54:11 AM UTC-4, Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..



Normally, blown outputs (is this what you mean by "end"?) will open fuses or low value resistors.

You really need a meter to go farther. If you get one or have one, you can compare voltages and resistance from the good side to the bad. If the receiver has a pre-amp out and in (or tape monitor) arrangement, you can reverse those to see if the problem trades sides. If it uses metal U shaped jumpers, remove them and use RCA patch cords to cross swap.

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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Fri, 5 Oct 2018 17:54:06 +0200, Steff wrote:

Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..

Try pushing the tape monitor and other push button switches on the
front panel a few times to see if the channel comes back. If it does,
spray the switch with DeOxit 5 or equivalent.
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

In article ,
Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?


Those are possibilities. Here's what I would suggest for further
troubleshooting. [Turn the power off before changing any cable
settings, of course.]

First: the manual and schematic show that the preamp and amp are
linked together via a set of jumpers on the back panel, going from
"pre amp out" to "main amp in". First thing to do is remove and
re-insert the jumpers, to see if you simply have a bad connection in
the connectors there. If removing and re-inserting fixes the problem,
then clean the connectors and jumpers with contact cleaner, reinsert,
and you should be OK.

Second thing to do is disconnect those jumpers, and replace them with
a standard red/black RCA-connector interconnect cable. This time,
swap the two channels - connect the left channel "pre out" to the
right channel "amp in", and vise versa.

If the problem remains in the left channel, then the fault lies in the
amplifier section.

If the problem moves over to the right channel, then the fault lies in
the preamp section.

If it's in the amp section: it might be the fuses (I'm not sure if
these are among the ones you checked). It could be bad speaker on/off
switches, but it seems unlikely that you've had the same failure in
the A and B channel switches (but it is possible... the speaker-B
switch might have failed long ago and you might not have noticed it
until now).

If the switches and fuses are all OK, and you're confident that the
amp is getting a valid input signal, then you'd need to trace the
signal through the amp section with a 'scope and DMM - see if your
B1/B2 power supply voltages are OK, and see how far the signal gets
through the left-channel amp before it vanishes.

If it's a failure in the preamp section (if the dead channel "moves"
when you switch the cabling between preamp and amp) then I think the
big two suspects would be:

- Bad, or dirty selector switches. In particular the "tape monitor"
switches for Tape 1 and Tape 2 are both right in the signal
path... if one of these has an open contact you'd lose a channel.
It looks as if the "tone control defeat" switch is also a suspect,
for the same reason.

- An electrolytic interstage coupling capacitor which has failed in
an "open" state.

Here, also, signal tracing is your friend. Feed a known-good line
level signal into the "tape 2 in" jacks, turn on "tape monitor 2", and
see if you get a good signal... this is the last input "in the path".
If that one works OK, try "tape 1 in" and the "tape monitor 1" switch
setting. If that works OK, use "aux". With this approach you're
working "backwards" from the preamp/amp interconnect, looking back
along the circuitry a step at a time to see how far back you can go
before the signal disappears.

I've seen enough older receivers/preamps with dirty-switch problems
that this is my lead suspect in cases like this. There's a reasonable
chance that cleaning all the switches will fix your problem. Put a
small squirt of DeOxIt D-5 into each switch, operate the switches a
dozen times or so to break up any old grease and dirt and oxide and
tobacco-smoke tar and etc., use another small squirt to flush out and
lubricate the contacts. Put a small squirt into each RCA jack, then
plug and unplug a cable a few times to break up the oxides and
crud. Let dry for a few minutes, then test again.

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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

You can narrow this down to the AMP section by removing the shorting plugs (pre-amp out to AMP in metal plugs) and replacing them with an RCA cable.

Let assume that the left channel is not working. Using a standard RCA to RCA cable, connect the left pre-amp out to the right AMP-in. If the right channel has sound as expected, then the pre-amp section is OK and the problem is with the amp section.

With the power off using a meter, A/B the left and right channels. Measurements of the corresponding components should measure about the same.
If you have access without the possibility of shorting components, use a DC meter and measure some voltage points. Again, the two channels should measure the same.

With the symptom of slight sound in the output, I would suspect that a voltage is missing. You may have an open resistor that feeds the output section.


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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Friday, October 5, 2018 at 8:54:11 AM UTC-7, Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..


You got some very good advice already. Just want to point out that failed output (end) transistors nearly ALWAYS short out and blow fuses. I've replaced thousands over the years.

I also want to point out that soldering as an electrician is probably different from soldering in a receiver. I recommend getting an old piece of electronics to try replacing a component and see if you can do it reliably. Better to find out on a piece of junk. Older circuit boards have a higher failure rate due to excessive heat. I had an old Sony board where the pads lifted too easily with a 700° tip but were OK with a 600° tip (Metcal).

I like old HK gear and would prefer to hear you have it working again.

G²
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

Den 2018-10-07 kl. 03:24, skrev :
On Friday, October 5, 2018 at 8:54:11 AM UTC-7, Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..


You got some very good advice already. Just want to point out that failed output (end) transistors nearly ALWAYS short out and blow fuses. I've replaced thousands over the years.

I also want to point out that soldering as an electrician is probably different from soldering in a receiver. I recommend getting an old piece of electronics to try replacing a component and see if you can do it reliably. Better to find out on a piece of junk. Older circuit boards have a higher failure rate due to excessive heat. I had an old Sony board where the pads lifted too easily with a 700° tip but were OK with a 600° tip (Metcal).

I like old HK gear and would prefer to hear you have it working again.

G²

I love HK products and specially the older septon ones. So giving life
to my old 930 have high priority for me as well. Mu dad buy it new and
had some JNL speakers with it.. I got is when I left home in 1979 as a
19 year old and it have been with me ever since, so ofcourse I will try
to keep it alive. Best Amp I ever had. I did have a Sansui that was OK
but still this one is the best.

I also have an oscilloscope and multimeter så I will try to separate the
pre amp from the poweramp and se if the prombel is located in the power
amp for sure. I already order some effekt transistors to prepare to
change them since i Still belive it is in the "end transistors"
I found 3 off them in Italy for a decent price (25 USD for 3)

So thanks so far for all advise I keep updating until it works hopefully
with all you guys help.

Sorry for my English My native language is Swedish so bare with me please.


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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Sunday, October 7, 2018 at 4:06:45 PM UTC-4, Steff wrote:
Den 2018-10-07 kl. 03:24, skrev :
On Friday, October 5, 2018 at 8:54:11 AM UTC-7, Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..


You got some very good advice already. Just want to point out that failed output (end) transistors nearly ALWAYS short out and blow fuses. I've replaced thousands over the years.

I also want to point out that soldering as an electrician is probably different from soldering in a receiver. I recommend getting an old piece of electronics to try replacing a component and see if you can do it reliably. Better to find out on a piece of junk. Older circuit boards have a higher failure rate due to excessive heat. I had an old Sony board where the pads lifted too easily with a 700° tip but were OK with a 600° tip (Metcal).

I like old HK gear and would prefer to hear you have it working again.

G²

I love HK products and specially the older septon ones. So giving life
to my old 930 have high priority for me as well. Mu dad buy it new and
had some JNL speakers with it.. I got is when I left home in 1979 as a
19 year old and it have been with me ever since, so ofcourse I will try
to keep it alive. Best Amp I ever had. I did have a Sansui that was OK
but still this one is the best.

I also have an oscilloscope and multimeter så I will try to separate the
pre amp from the poweramp and se if the prombel is located in the power
amp for sure. I already order some effekt transistors to prepare to
change them since i Still belive it is in the "end transistors"
I found 3 off them in Italy for a decent price (25 USD for 3)

So thanks so far for all advise I keep updating until it works hopefully
with all you guys help.

Sorry for my English My native language is Swedish so bare with me please..




Sad to say, you're English is better than many native speakers...

I've changed many hundreds of outputs over the years, and have never seen one "open". High current/wattage devices *generally* fail catastrophically, not open benignly, although there certainly are exceptions to every rule. So with a basic DMM, check for low ohm shorts. Out of circuit they should read a few hundred K ohms minimum if anything at all. On the diode scale, you should get two combinations that read about 0.600 if the outputs are silicon.

I can't speak for your particular HK, but most amplifiers (not all) use a common speaker protection relay so a shorted transistor on one side will prevent the speaker relay from engaging, rendering both sides mute. Your HK being an older vintage piece may be configured differently.



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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

OK. Read.

First of all that is a good piece. Not the most advanced but so what.

The amp is a standard quasi comp design, not hard at all.

Now, first of all for the outputs 2N3773s would be great. that is a JEDEC (US) number though and you might not be able to get them there. the originals are TO-3, try to stick with that and not use the plastic equivalent, I don't like how they mate to the original holes. the original design calls for less than a certain thermal resistance there and upsetting that is not good. If you got a friend in the US those 2N3773s are not expensive and fit alot more than just that amp.

So take the outputs out. Short the base and emitter terminals of each as well as TR 624 and 604 (?) the bias transistors emitter to collector, if unsure of the basing just short it all the way around. Not with the outputs though, the basing is clear enough, the pins are E and B, those are what you short. (not to the other transistor...)

Now use a DBT for the fuse whether it is blown or not. When powering up the lamp should light then dim gradually until it is about out. The voltage at the speaker outputs should be zero or close. If not, one of the drivers may be shorted, if you care to that can be checked with no power using the DVM on the -|- scale of course.

With a scope you should even be able to see an audio waveform at the output, put on some rock music, the waveform should be pretty much symmetrical up and down. DO NOT connect a load like a speaker or dummy or you will blow the drivers if they aren't already.

Once you got that all straightened out and have it with not outputs in then put in the new ones. Leave the short across that bias transistor and connect speakers. There will be much distortion at low levels getting almost clean as you approach maximum power.

Once it passes that test, remove power and discharge the filters. Remove the short from one of the bias transistors, power on, if that light does not dim as it did before there is a fault in the bias, do not run it like that load or not.

All this assumes the resistors that join at the speaker outputs have been checked and are not open. Usually there is no smoke or burn so they need to be tested electrically. forget the exact value, to measure it accurately you need the right equipment, either a meter on which you can null the lead resistance or a Kelvin connection. If it is not open, 95 % of the time it is good.

Those are the live tests mainly, there is not reason not to check the transistors and low value resistors before even starting the powered tests. Main thing you want id no open transistors and no shorted transistors.

These methods have made me a bunch of money because I do not waste silicon. And BTW, did you say something about 3 of them ? They need to be replaced in pairs. If one shorts, the feedback in the circuit tries to pull the voltage back to zero and that can exceed the design maximums of the other output in the channel.

If the original AC fuse is not blown use that meter and look for open resistors all over those output circuits, if anything shorts something has to give. If what gives it in the bias circuit you could lose your new outputs in less than a second, that is why the first run is done with zero bias.

As far as making sure the problem is in the output stage, just take a pair of RCA cables and switch left and right. If the problem switches to the other channel then all this is moot and now we are in the preamp. The scope will come in VERY handy if that is the case.

If it does go to the other channel a mono switch would be nice but I do not wee one. In this case you can just short the volume controls together, either the top (not grounded) side or the wipers, doesn't matter, if you get both channels then the problem is before that. At that point there ain't much left. (ain't is a word used only by those with exceptional command of the English language lol)
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Sunday, October 7, 2018 at 1:06:45 PM UTC-7, Steff wrote:
Den 2018-10-07 kl. 03:24, skrev :
On Friday, October 5, 2018 at 8:54:11 AM UTC-7, Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..


You got some very good advice already. Just want to point out that failed output (end) transistors nearly ALWAYS short out and blow fuses. I've replaced thousands over the years.

I also want to point out that soldering as an electrician is probably different from soldering in a receiver. I recommend getting an old piece of electronics to try replacing a component and see if you can do it reliably. Better to find out on a piece of junk. Older circuit boards have a higher failure rate due to excessive heat. I had an old Sony board where the pads lifted too easily with a 700° tip but were OK with a 600° tip (Metcal).

I like old HK gear and would prefer to hear you have it working again.

G²

I love HK products and specially the older septon ones. So giving life
to my old 930 have high priority for me as well. Mu dad buy it new and
had some JNL speakers with it.. I got is when I left home in 1979 as a
19 year old and it have been with me ever since, so ofcourse I will try
to keep it alive. Best Amp I ever had. I did have a Sansui that was OK
but still this one is the best.

I also have an oscilloscope and multimeter så I will try to separate the
pre amp from the poweramp and se if the prombel is located in the power
amp for sure. I already order some effekt transistors to prepare to
change them since i Still belive it is in the "end transistors"
I found 3 off them in Italy for a decent price (25 USD for 3)

So thanks so far for all advise I keep updating until it works hopefully
with all you guys help.

Sorry for my English My native language is Swedish so bare with me please..



Hi Steff,

Your English is way better than my non-existent Swedish.

So you have a scope and meter and are way ahead of the game. Most folks
don't realize they also have a test generator called their computer. I make test signals frequently with Adobe Audition 3. Audacity is free and works as well.

I would bet money the output transistors have not failed. I got the service manual from HiFiEngine and noted the only thing between the speaker connector and the amplifier is the speaker switches for local and remote speakers. There is no 'protection' or fault detection or relays

The first thing to do is verify all the power supplies are good. I can't make out if the amplifiers run on +/- 34 or +/- 39 Volts. While the power amps have twin power supplies, the signal system (AM,FM, phono and tone controls) run off the left channel transformer (+B2, -B2) The B3 supply should be around 20 Volts positive and should have nearly no ripple. You'd see ripple with your scope set to AC coupling and turn up the sensitivity to 50 mV per division. I would expect it to be 0-5mV.

If I had it on the bench I would run a 1KHz signal into AUX 1 or 2 and verify normal signal at the 'preamp out' jumpers on the back of the unit. If you want to test tone controls you can generate a 'chirp' (frequency sweep) in Audacity and observe the output on the scope. I predict no problems at preamp output. With no speakers connected (speaker switch off is
the same thing) there should be sound on the headphones even if the speaker fuses are blown.

Good luck and let us know.

G²



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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Sunday, October 7, 2018 at 6:58:59 PM UTC-5, John-Del wrote:

Sad to say, you're English is better than many native speakers...


Yup. the mistakes are mistakes, not laziness.



I've changed many hundreds of outputs over the years, and have never seen one "open".


I have, but they are usually intermittent.

I can't speak for your particular HK, but most amplifiers (not all) use a common speaker protection relay so a shorted transistor on one side will prevent the speaker relay from engaging, rendering both sides mute. Your HK being an older vintage piece may be configured differently.


Actually none at all, there is no protection, no relay, delay or even output current limiting.

It is still a good piece. The outputs are hefty enough to handle a sub 4 ohm real load, looks like a fairly healthy FM as well with the totally shielded front end. It's not PLL stereo but if it is stable there is no reason it can't perform. It doesn't have the best tone controls of lo and hi cut filters but eh, can't have everything.
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Sunday, October 7, 2018 at 10:09:40 PM UTC-4, wrote:
On Sunday, October 7, 2018 at 6:58:59 PM UTC-5, John-Del wrote:

Sad to say, you're English is better than many native speakers...


Yup. the mistakes are mistakes, not laziness.


You missed the sarkasm...



I've changed many hundreds of outputs over the years, and have never seen one "open".


I have, but they are usually intermittent.


Never saw one, but I did qualify my statement by saying that anything is possible. I've lived long enough to know that odd things happen. The only thing close is that I found a horiz output in an RCA CTC120 (or thereabouts) that was open. That was the first and only high power device I ever saw open. I still don't thing Steff has an open output.


I can't speak for your particular HK, but most amplifiers (not all) use a common speaker protection relay so a shorted transistor on one side will prevent the speaker relay from engaging, rendering both sides mute. Your HK being an older vintage piece may be configured differently.


Actually none at all, there is no protection, no relay, delay or even output current limiting.


Yikes. I remember a Hitachi receiver in the shop back in the early 80s that would destroy speakers whenever it wanted to. Play nice, short loud hum, speaker smoke. Turned out to be one of those weird Hitachi small signal transistors with the slanted top. Once every few days it would direct couple DC.
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

here is a tip,

wire an outlet box with a duplex outlet and a switch.

wire the outlet so the two outlets are in SERIES and in series with the switch..

Plug your unit into one outlet and plug a 100 Watt INCANDESCENT light into the other outlet.

Use the switch to turn on/off the power. This makes it easy to turn OFF all the power when you are working on the unit.

Also the bulb will limit the current if there is a fault. If the bulb glows brightly, there is still a fault and this will protect the new parts that you just put in.

mark



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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

Mouser Electronics stocks 2N3772 output transistors from ON Semi-conductor. They run about US$3.50 each in lots of 10 (which will assure you of matching at least four, if not more), and shipping across the Ocean is not so much as to preclude that option.

https://www.mouser.com/_/?Keyword=2N3772G

That is a high-powered TO3-case PNP output transistor that is capable of 60+ watts in PP. I will retrofit them anywhere appropriate, and they are very nearly a drop-in replacement for the 2N3055 or equivalent. I state 'very nearly' as some devices may require a bias adjustment.

Note that in my experience, one or another of the driver pair often fails and takes the outputs with it, or the outputs fail and take a driver-or-two. Do also check for failed diodes - that failure may be invisible - and failed caps. As previously noted, comparing channel-to-channel is key.

Yes, that HK Series is worth the trouble.

Peter Wieck
Melrose Park, PA
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

In article ,
says...

Mouser Electronics stocks 2N3772 output transistors from ON Semi-conductor. They run about US$3.50 each in lots of 10 (which will assure you of matching at least four, if not more), and shipping across the Ocean is not so much as to preclude that option.

https://www.mouser.com/_/?Keyword=2N3772G

That is a high-powered TO3-case PNP output transistor that is capable of 60+ watts in PP. I will retrofit them anywhere appropriate, and they are very nearly a drop-in replacement for the 2N3055 or equivalent. I state 'very nearly' as some devices may require a bias adjustment.

Note that in my experience, one or another of the driver pair often fails and takes the outputs with it, or the outputs fail and take a driver-or-two. Do also check for failed diodes - that failure may be invisible - and failed caps. As previously noted, comparing channel-to-channel is key.

Yes, that HK Series is worth the trouble.

Peter Wieck
Melrose Park, PA



They are NPN , not PNP.

OUtside of that the 2n3771, 2n3772 and 2n3773 are all similar. They are
a much higher power than the 2n3055 and I also use them to replace the
2n3055 in most power supply circuits.



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"Never saw one, but I did qualify my statement by saying that anything is possible. "

Well, I have repaired thousands upon thousands and actually have seen them go that way about a half dozen times. It is not common to say the least.

One weird time I had a connection to the base of a horizontal output, IIRC it was an NAP, and that SOB oscillated on its own ! I am initially looking for a sync problem and it was nothing of the sort. Miller effect on steroids or whatever, I mean how the hell did... ? What's more is it was only a few hundred Hz off, and high not low.

"Yikes. I remember a Hitachi receiver in the shop back in the early 80s that would destroy speakers whenever it wanted to. Play nice, short loud hum, speaker smoke. "


I had a Sansui 8900 do that due to a transistor socket. Blew both woofers in one of the guy's EPIs. I sold him a pair and found out that the polarity of the ones I had were reversed from the original. I mean red to red, black to black, out of phase.

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"Note that in my experience, one or another of the driver pair often fails and takes the outputs with it, or the outputs fail and take a driver-or-two."

That is the reason for the procedure I described.

The 2N3773 is better in another way, the gain curve. The 3773 still has 35 HFE at 10 amps, while a 3055 drops to 10. At 5 amps the 3773 is 60 and the 3055 is 30. Both of them start around 100 or so at like a half amp.

"Yes, that HK Series is worth the trouble. "


Absolutely, but I recommend speaker fuses. One good trick to keep the fuses form introducing distortion at high level low frequencies (this is not audiopholery, it is measurable) is to make a high value bipolar out of like 2 8,200 uFs in series +to+ and put it across the fuse. That only DC or very low frequencies will blow it. For this amp all you would need is 35 volt units.

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Absolutely, but I recommend speaker fuses. One good trick to keep the fuses form introducing distortion at high level low frequencies (this is not audiopholery, it is measurable) is to make a high value bipolar out of like 2 8,200 uFs in series +to+ and put it across the fuse. That only DC or very low frequencies will blow it. For this amp all you would need is 35 volt units.


I agree the distortion is measurable but it may still be audiopholery.

How much are we talking about due to the fuse?

And how much distortion will the speaker itself create at that frequency/ level?

m

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"How much are we talking about due to the fuse?"

That has to do with the type of fuse and the current drawn by the speaker since it is dependent upon the low thermal mass of the fuse element. The resistance increases with temperature. All it takes is a part of that element to get warm. A large enough capacitor across it will keep that from happening. In fact if you want to risk it to save a few bucks you can get a super high capacitance with low ESR and a lower voltage rating. Of course if the fuse blows then the cap will explode.

"And how much distortion will the speaker itself create at that frequency/ level? "


People who care and buy expensive speakers usually get quite low distortion from them. My Boston Acoustics A-150s IIRC were rated 0.7 % which is phenomenally low for a speaker. Really, most of the cheap junk is more like 3 - 5 % at any decent listening level and it is mostly odd order harmonics. However with a decent crossover that is just harmonic distortion, the fuse will also create intermodulation distortion because all frequencies go through it. I would say that is much more audible.

Lower power ratings don't really help because you would use a commensurately lower value fuse and its thermal mass will be less. A slow blow is probably better but then it comes down to how much abuse to which you are willing to subject your woofers. Some of them are quite expensive.
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

Den 2018-10-08 kl. 22:48, skrev Ralph Mowery:
In article ,
says...

Mouser Electronics stocks 2N3772 output transistors from ON Semi-conductor. They run about US$3.50 each in lots of 10 (which will assure you of matching at least four, if not more), and shipping across the Ocean is not so much as to preclude that option.

https://www.mouser.com/_/?Keyword=2N3772G

That is a high-powered TO3-case PNP output transistor that is capable of 60+ watts in PP. I will retrofit them anywhere appropriate, and they are very nearly a drop-in replacement for the 2N3055 or equivalent. I state 'very nearly' as some devices may require a bias adjustment.

Note that in my experience, one or another of the driver pair often fails and takes the outputs with it, or the outputs fail and take a driver-or-two. Do also check for failed diodes - that failure may be invisible - and failed caps. As previously noted, comparing channel-to-channel is key.

Yes, that HK Series is worth the trouble.

Peter Wieck
Melrose Park, PA



They are NPN , not PNP.

OUtside of that the 2n3771, 2n3772 and 2n3773 are all similar. They are
a much higher power than the 2n3055 and I also use them to replace the
2n3055 in most power supply circuits.


That is correct.. The smaller TO3 ones have small "collers" on them and
I noticed that the aluminum coolers dont have to much contakt with the
shell of the transistor. The grease have dried out and the aluminum
cooler did not have much contakt with the metall casing. I think this is
a think for others to have a look at in therir working units. since bad
cooling can kill this NPN transistors.

Cleaning and new grease would make wonders I think.



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"The grease has dried out..."

I guess now would be a good time to dispel this old husband's tale.

When the union between heatsink and transistor is undisturbed, dried out grease that is like cement is perfectly fine. I have conducted a few studies on it albeit subjective. That is that the temperature difference between a transistor and the heatsink to which it is mounted is not significant, AS LONG AS IT IS NOT DISTURBED.

That assumes it was installed properly in the first place.

First of all you never spread the compound, you put a dab or a bead where it will be squished out as it is tightened. this eliminates air pockets. If you have a big air pocket between there you would be better off with no compound at all.

Granted, the old dried out compound does not have as good thermal conductivity as nice new wet goop, but it is seated over the years and works quite well. If you doubt what I say take a meat thermometer and check the case of a TO-3 and its heatsink on one that has been there for decades and ne that you remount with new goop now. In fact to make sure there is no error, clean those surfaces with "things". Scrub pads, alcohol, maybe acetone, and finish with a coffee fitter to get the surface nice and smooth. Apply a dab or bead right where the ounting will exert the mos even force, on a TO-3 for example, that will be about in the center and it is normal for some of the goop to squeeze through the holes for the pins. then get that thermometer out after using the unit to get the heat up, like on a stereo amp, run both channels at like 1/3rd power for an hour, that'll warm er up. As soon as you detect heat, measure. It has JUST been produced so it is still conducting to the heatsink. That would be the most accurate comparative test, but not for absolutes. It is not a number except for "how much" one is better than the other. Your actual calories of heat/watts dissipation and all that **** matters not. Iti s simply better or worse. Try it.
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An infra-red heat gun is better at very close range. It will show variations of fractions of a degree.

Also very good for pinpointing hot-spots. Within a couple of inches, the spread is 1/6" for a standard 12:1 unit. There are narrower devices, but they are comparatively pricey.

Peter Wieck
Melrose Park, PA
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On Friday, October 12, 2018 at 8:36:35 AM UTC-4, wrote:
"The grease has dried out..."


I guess now would be a good time to dispel this old husband's tale.

When the union between heatsink and transistor is undisturbed, dried out grease that is like cement is perfectly fine.


You beat me to it. It's not the liquid component of heat sink compound that transfer heat, it's the solids that are suspended in the goop. The compound may get hard, but the solids are still packed between gaps doing their job.


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On 10/12/2018 10:19 AM, John-Del wrote:
On Friday, October 12, 2018 at 8:36:35 AM UTC-4,
wrote:
"The grease has dried out..."


I guess now would be a good time to dispel this old husband's tale.


When the union between heatsink and transistor is undisturbed,
dried out grease that is like cement is perfectly fine.


You beat me to it. It's not the liquid component of heat sink
compound that transfer heat, it's the solids that are suspended in
the goop. The compound may get hard, but the solids are still packed
between gaps doing their job.


Provided they're really undisturbed. Thermal cycling can cause
delamination problems that don't occur with the oil present.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
https://hobbs-eo.com


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On Friday, October 12, 2018 at 9:24:31 AM UTC-4, Phil Hobbs wrote:

Providing that the thermal infrared emissivity of the surface is high,
e.g. plastic or glass. A dab of grease or some tape will make it work a
lot better.


I have not experienced that issue, for the record. What I find is that accuracy starts to suffer as the battery gets weak. I view them the same as smoke-alarm batteries - 2x per year, whether I need it or not. And the used batteries are put aside for my increasing number of novelty radios that the grandkids are fighting over. Not in them, but with them for demonstration purposes.

Peter Wieck
Melrose Park, PA
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On Tuesday, October 16, 2018 at 1:03:31 PM UTC-4, Phil Hobbs wrote:

Your accuracy requirements aren't high, then. A shiny metal surface can
easily show up as 90% room reflection and 10% surface emission. A bit
of tape will reverse those numbers.


Perhaps not. 90% of the use is to verify that I am not looking at a freeze-out on an AHU coil or at the discharge temperature of a chiller. And in such cases, it is pretty much go/no-go. I am not the mechanic, but I have learned over the years that "trust but verify" does not only apply to the former Soviets.

But, for 10% of the use, it is to let office workers, docs or other staff know the temperature in their space. The docs have, on more than a few occasions, pulled out a thermometer of their own - and so far, they and my little heat gun have agreed.

On rare occasion, I will use it at home to verify radiator temperature against the gauge on the boiler, or to look for hot-spots in some bit of audio or radio equipment, or other. And, if one tube on an output pair is acting differently from another, I understand I have an issue.

Peter Wieck
Melrose Park, PA
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"Provided they're really undisturbed. Thermal cycling can cause
delamination problems that don't occur with the oil present. "

What I consider the better TO-3s are aluminum, not steel. Another advantage is that they won't bend as much if the mounting surface is not perfectly flat.

T


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wrote:



What I consider the better TO-3s are aluminum, not steel.



** Though once common, Aluminium TO3 paks are no longer used by most manufacturers due to problems with thermal expansion of the aluminium base causing microscopic cracking of silicon chips.

Thermal expansion of aluminium is about 7 times greater than that of silicon, limiting the number of full thermal cycles such devices were good for.

https://www.engineeringtoolbox.com/t...als-d_859.html

Steel and copper alloy packs are used instead, with most having a "coin" made of a metal with intermediate rate of expansion soldered between the chip and the pak.



Another advantage is that they won't bend as much if the mounting
surface is not perfectly flat.


** Yuck. Better use only flat heatsinks.




..... Phil
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On Monday, October 8, 2018 at 12:28:00 PM UTC-4, wrote:
here is a tip,

wire an outlet box with a duplex outlet and a switch.

wire the outlet so the two outlets are in SERIES and in series with the switch..

Plug your unit into one outlet and plug a 100 Watt INCANDESCENT light into the other outlet.


I wonder what it takes for a guy to find a house where all the 120v outlets are wired like that.
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On Monday, October 22, 2018 at 9:01:53 PM UTC-5, wrote:
On Monday, October 8, 2018 at 12:28:00 PM UTC-4, wrote:
here is a tip,

wire an outlet box with a duplex outlet and a switch.

wire the outlet so the two outlets are in SERIES and in series with the switch..

Plug your unit into one outlet and plug a 100 Watt INCANDESCENT light into the other outlet.


I wonder what it takes for a guy to find a house where all the 120v outlets are wired like that.


Make sure there is a plug on it, do not wire it to the house wiring. Very against code.
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