I have an Onkyo TX-82 stereo receiver.

What happens is that, at random moments during use, the speaker
protection relay may open and cut the sound and then close.

I've tried reflowing all solder joints on the power amp board and
replaced various electrolytic capacitors, but to no avail. The
receiver keeps cutting out at random times.

The receiver seems to amplify normally, even up to the point where the
relay opens.

I'm guessing that the relay itself could be at fault, but how? I
physically tap the relay during use and it doesn't exhibit any faults.

Any suggestions on what could be going on?

wrote in message
...
I have an Onkyo TX-82 stereo receiver.

What happens is that, at random moments during use, the speaker
protection relay may open and cut the sound and then close.

I've tried reflowing all solder joints on the power amp board and
replaced various electrolytic capacitors, but to no avail. The
receiver keeps cutting out at random times.

The receiver seems to amplify normally, even up to the point where the
relay opens.

I'm guessing that the relay itself could be at fault, but how? I
physically tap the relay during use and it doesn't exhibit any faults.

Any suggestions on what could be going on?

Bad joints on the relay coil connections. Bad joints in the power supply
causing one rail to drop out momentarily. Bad joints in the relay control /
fault sense circuit. Resistor on relay delay timing going high / open.
Timing cap int o/c. Genuine problem such as defective speaker or wiring.
Those are the most common problems I come across.

Arfa

wrote in message
...
I have an Onkyo TX-82 stereo receiver.

What happens is that, at random moments during use, the speaker
protection relay may open and cut the sound and then close.

I've tried reflowing all solder joints on the power amp board and
replaced various electrolytic capacitors, but to no avail. The
receiver keeps cutting out at random times.

The receiver seems to amplify normally, even up to the point where the
relay opens.

I'm guessing that the relay itself could be at fault, but how? I
physically tap the relay during use and it doesn't exhibit any faults.

Any suggestions on what could be going on?


You can probably look elsewhere for the fault. I would first suspect that the
circuitry that controls the relay, i.e., the protection circuitry, is
activating.

Some possible reasons that the protection circuitry is opening the relay...
(1) DC offset voltage is appearing at the speaker terminals. Causes... Idle
current set wrong or component failure in the amplifier chain causing the offset
to go haywire.
(2) Temperature compensation circuitry faulty. Causes... defective temperature
sensing component (thermistor, diode, transistor).
(3) Protection circuitry faulty. Causes... component failure in that area.
(4) Anything else that would upset the DC balance in the amplifier.

Things to look for:
Check for DC voltage present at the speaker terminals. If it's more than a few
millivolts, you need to find the reason for it.
Is the DC offset only on one channel (more likely) or both (unlikely)? Use the
good channel to compare voltage measurements along the amplifier chain and try
to isolate the bad stage.
Does the protection relay activate with no audio, or only with audio present?
Do you have a schematic of the unit?
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Experience: What you get when you don't get what you want

On Aug 16, 8:34*pm, "DaveM" wrote:
wrote in message

...



I have an Onkyo TX-82 stereo receiver.

What happens is that, at random moments during use, the speaker
protection relay may open and cut the sound and then close.

I've tried reflowing all solder joints on the power amp board and
replaced various electrolytic capacitors, but to no avail. *The
receiver keeps cutting out at random times.

The receiver seems to amplify normally, even up to the point where the
relay opens.

I'm guessing that the relay itself could be at fault, but how? *I
physically tap the relay during use and it doesn't exhibit any faults.

Any suggestions on what could be going on?

You can probably look elsewhere for the fault. *I would first suspect that the
circuitry that controls the relay, i.e., the protection circuitry, is
activating.

Some possible reasons that the protection circuitry is opening the relay....
(1) DC offset voltage is appearing at the speaker terminals. *Causes... Idle
current set wrong or component failure in the amplifier chain causing the offset
to go haywire.
(2) Temperature compensation circuitry faulty. *Causes... defective temperature
sensing component (thermistor, diode, transistor).
(3) Protection circuitry faulty. *Causes... component failure in that area.
(4) Anything else that would upset the DC balance in the amplifier.

Things to look for:
Check for DC voltage present at the speaker terminals. *If it's more than a few
millivolts, you need to find the reason for it.
Is the DC offset only on one channel (more likely) or both (unlikely)? *Use the
good channel to compare voltage measurements along the amplifier chain and try
to isolate the bad stage.
Does the protection relay activate with no audio, or only with audio present?
Do you have a schematic of the unit?
--
Dave M
MasonDG44 at comcast dot net *(Just substitute the appropriate characters in the
address)

Experience: What you get when you don't get what you want

The relay trips whether or not there is any audio and whether or not
the power amp circuit has any load or not.

Checking for DC in the speaker terminals. Bank A left reads 8.3mV.
Bank A right reads 5.9mV. Bank B left reads 8.4mV. Bank B right reads
6.1mV.

Measures taken when receiver is idle with no source.

Unfortunately, I have no service data for this receiver.

Checking for DC in the speaker terminals. Bank A left reads 8.3mV.
Bank A right reads 5.9mV. Bank B left reads 8.4mV. Bank B right reads
6.1mV.

Have you sat there watching the meter to see if the offset jumps up when the
relay opens? (I'm sure you have better things to do with your time!) Some
DMMs have a trending feature that keeps track of the highest voltage.

Arfa's suggestions are a good place to start.

On Aug 16, 9:20*pm, "William Sommerwerck"
wrote:
Checking for DC in the speaker terminals. Bank A left reads 8.3mV.
Bank A right reads 5.9mV. Bank B left reads 8.4mV. Bank B right reads
6.1mV.

Have you sat there watching the meter to see if the offset jumps up when the
relay opens? (I'm sure you have better things to do with your time!) Some
DMMs have a trending feature that keeps track of the highest voltage.

Arfa's suggestions are a good place to start.

Right now, I want to figure out what is going on and I have the time
at this moment to do that.

I measured the power and, on the left channel, the offset fluctuates
between a peak of 11.3 mV and 8.3 mV. Is this significant?

Unfortunately, I missed the meter reading right at the moment the
protection relay tripped.

On Aug 16, 8:34*pm, "DaveM" wrote:
wrote in message

...



I have an Onkyo TX-82 stereo receiver.

What happens is that, at random moments during use, the speaker
protection relay may open and cut the sound and then close.

I've tried reflowing all solder joints on the power amp board and
replaced various electrolytic capacitors, but to no avail. *The
receiver keeps cutting out at random times.

The receiver seems to amplify normally, even up to the point where the
relay opens.

I'm guessing that the relay itself could be at fault, but how? *I
physically tap the relay during use and it doesn't exhibit any faults.

Any suggestions on what could be going on?

You can probably look elsewhere for the fault. *I would first suspect that the
circuitry that controls the relay, i.e., the protection circuitry, is
activating.

Some possible reasons that the protection circuitry is opening the relay....
(1) DC offset voltage is appearing at the speaker terminals. *Causes... Idle
current set wrong or component failure in the amplifier chain causing the offset
to go haywire.
(2) Temperature compensation circuitry faulty. *Causes... defective temperature
sensing component (thermistor, diode, transistor).
(3) Protection circuitry faulty. *Causes... component failure in that area.
(4) Anything else that would upset the DC balance in the amplifier.

Things to look for:
Check for DC voltage present at the speaker terminals. *If it's more than a few
millivolts, you need to find the reason for it.
Is the DC offset only on one channel (more likely) or both (unlikely)? *Use the
good channel to compare voltage measurements along the amplifier chain and try
to isolate the bad stage.
Does the protection relay activate with no audio, or only with audio present?
Do you have a schematic of the unit?
--
Dave M
MasonDG44 at comcast dot net *(Just substitute the appropriate characters in the
address)

Experience: What you get when you don't get what you want

I think I may have solved the problem.

I managed to find the service manual and performed a test and
adjustment of the idling current.

The service manual states that the idling current at open load must be
7.5 mV with a tolerance of 1.5 mV

Left channel was about spot-on at 7.0mV, but the right channel was WAY
off at over 30 mV! Seems the trim pot that controlled the idling
current has changed in value.

Anyways, I readjusted both trim pots until I got the voltage spot-on
to 7.5 mV. Hopefully, that will fix it.

However, I am concerned about the fact that the pot on the right
output had drifted so drastically so I am entertaining the notion of
finding a replacement set of pots and redoing the idling adjustment.

What do you guys think?

On Sat, 16 Aug 2008 15:45:37 -0700 (PDT), put
finger to keyboard and composed:

I have an Onkyo TX-82 stereo receiver.

What happens is that, at random moments during use, the speaker
protection relay may open and cut the sound and then close.

I've tried reflowing all solder joints on the power amp board and
replaced various electrolytic capacitors, but to no avail. The
receiver keeps cutting out at random times.

The receiver seems to amplify normally, even up to the point where the
relay opens.

I'm guessing that the relay itself could be at fault, but how? I
physically tap the relay during use and it doesn't exhibit any faults.

Any suggestions on what could be going on?

Assuming that the protection involves some current sensing or DC
voltage sensing components in each channel, then why not disconnect
the relevant components one channel at a time? I would think that you
would not risk any damage by doing this, since you are able to
reproduce the fault with the speakers disconnected.

Other replies have focused on looking for a DC voltage on the outputs,
but I've just been looking at the protection circuit for a current
model Onkyo receiver (TX-8211) that appears to monitor the load
current in the 0.22 ohm emitter resistors of the output transistor
pair. If either resistor were to intermittently go open, then this
would trigger the protection. I have seen this problem in a car amp.
In that instance, one of the pins of a ceramic emitter resistor
fractured due to vibration.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

... I've just been looking at the protection circuit for a current
model Onkyo receiver (TX-8211) that appears to monitor the load
current in the 0.22 ohm emitter resistors of the output transistor
pair. If either resistor were to intermittently go open, then this
would trigger the protection. I have seen this problem in a car amp.
In that instance, one of the pins of a ceramic emitter resistor
fractured due to vibration.

- Franc Zabkar

Interesting thought.

According to the schematics and parts list, if I'm reading it right,
Q508 and Q509 (transistor pairs for the left) work with R512 and R513,
which are a matched pair of metal plate resistors rated at 2W and .47
ohms. The right channel transistor pair are Q608 and Q609 and their
resistors are R612 and R613. The resistors on the right channel are
identical with those that are on the left, of course.

So, how would I go about testing the resistors? Would I lightly tap
on each one with a plastic probe and see whether or not the protection
relay trips?

wrote in message
...
On Aug 16, 8:34 pm, "DaveM" wrote:
wrote in message

...



I have an Onkyo TX-82 stereo receiver.

What happens is that, at random moments during use, the speaker
protection relay may open and cut the sound and then close.

I've tried reflowing all solder joints on the power amp board and
replaced various electrolytic capacitors, but to no avail. The
receiver keeps cutting out at random times.

The receiver seems to amplify normally, even up to the point where the
relay opens.

I'm guessing that the relay itself could be at fault, but how? I
physically tap the relay during use and it doesn't exhibit any faults.

Any suggestions on what could be going on?

You can probably look elsewhere for the fault. I would first suspect that
the
circuitry that controls the relay, i.e., the protection circuitry, is
activating.

Some possible reasons that the protection circuitry is opening the
relay...
(1) DC offset voltage is appearing at the speaker terminals. Causes...
Idle
current set wrong or component failure in the amplifier chain causing the
offset
to go haywire.
(2) Temperature compensation circuitry faulty. Causes... defective
temperature
sensing component (thermistor, diode, transistor).
(3) Protection circuitry faulty. Causes... component failure in that area.
(4) Anything else that would upset the DC balance in the amplifier.

Things to look for:
Check for DC voltage present at the speaker terminals. If it's more than a
few
millivolts, you need to find the reason for it.
Is the DC offset only on one channel (more likely) or both (unlikely)? Use
the
good channel to compare voltage measurements along the amplifier chain and
try
to isolate the bad stage.
Does the protection relay activate with no audio, or only with audio
present?
Do you have a schematic of the unit?
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters
in the
address)

Experience: What you get when you don't get what you want

The relay trips whether or not there is any audio and whether or not
the power amp circuit has any load or not.

Checking for DC in the speaker terminals. Bank A left reads 8.3mV.
Bank A right reads 5.9mV. Bank B left reads 8.4mV. Bank B right reads
6.1mV.

&&&&&

all quite normal

Monitor the main +/- DC rails for changes/imbalance. Monitor the voltage
over any zener diodes associated with the protection circuitry.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

wrote in message
...
On Aug 16, 9:20 pm, "William Sommerwerck"
wrote:
Checking for DC in the speaker terminals. Bank A left reads 8.3mV.
Bank A right reads 5.9mV. Bank B left reads 8.4mV. Bank B right reads
6.1mV.

Have you sat there watching the meter to see if the offset jumps up when
the
relay opens? (I'm sure you have better things to do with your time!) Some
DMMs have a trending feature that keeps track of the highest voltage.

Arfa's suggestions are a good place to start.

Right now, I want to figure out what is going on and I have the time
at this moment to do that.

I measured the power and, on the left channel, the offset fluctuates
between a peak of 11.3 mV and 8.3 mV. Is this significant?

Unfortunately, I missed the meter reading right at the moment the
protection relay tripped.



It's hard to say whether or not that is significant. In itself, in terms of
absolute voltage, it is not significant. Imbalances up to about 20mV are not
uncommon, and are nothing for concern. However, the fact that it is
fluctuating may indicate that some component is 'hovering' around its
breaking down point, or that one of the rails is not stable. It is not
really usual for the voltage, whatever its actual value, to fluctuate. Does
your DMM have a peak hold facility as suggested elsewhere? This will tell
you if the midpoint shifts substantially at the time of failure. However,
note that if the relay circuit is 'quick', it might be *too* quick for the
DMM to see the voltage increase, before the relay disconnects it, so really,
you need to be taking any measurements actually at the amplifier output,
prior to the relay.

Does this amp have a set of discrete component output stages, or are they
STK hybrids ?

Monitor the supply rails as well - particularly those to the output stages -
and see if they are moving by a similar amount as the output offset. In DC
coupled amps, a very tiny shift in conditions back in a preamp stage, can
upset the DC conditions so much in the output stages, as to cause a relay
trip-out, which can make them very frustrating to troubleshoot. Use the butt
end of a reasonable sized screwdriver to have a bit of a bash around, to see
if you can provoke the problem at will. If you can, then swap to a biro pen
to pin down the actual area, and possibly, component.

You can also try a hairdryer, and a can of freezer, both sides of the board.
Bad joints which don't readily show up with disturbance testing, are often
surprisingly sensitive to heat and cold. Does the problem seem to get worse
or better the longer the amp is on ? Is it worse when the amp is 'doing some
work' ? All possibly significant factors in arriving at a diagnosis.

Arfa

Monitor the main +/- DC rails for changes/imbalance. Monitor the voltage
over any zener diodes associated with the protection circuitry.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list onhttp://home.graffiti.net/diverse:graffiti.net/

Could the idling current being horridly off be a possible cause?

I managed to obtain the service manual and was able to measure voltage
for the idling current.

According to the service manual, voltage should be at 7.5mV with a
tolerance of +/- 1.5mV. Left channel measured in at around 7.0 mV,
but the right channel was measured at over 30.0 mV.

On Sat, 16 Aug 2008 23:36:58 -0700 (PDT), put
finger to keyboard and composed:

... I've just been looking at the protection circuit for a current
model Onkyo receiver (TX-8211) that appears to monitor the load
current in the 0.22 ohm emitter resistors of the output transistor
pair. If either resistor were to intermittently go open, then this
would trigger the protection. I have seen this problem in a car amp.
In that instance, one of the pins of a ceramic emitter resistor
fractured due to vibration.

- Franc Zabkar

Interesting thought.

According to the schematics and parts list, if I'm reading it right,
Q508 and Q509 (transistor pairs for the left) work with R512 and R513,
which are a matched pair of metal plate resistors rated at 2W and .47
ohms. The right channel transistor pair are Q608 and Q609 and their
resistors are R612 and R613. The resistors on the right channel are
identical with those that are on the left, of course.

So, how would I go about testing the resistors? Would I lightly tap
on each one with a plastic probe and see whether or not the protection
relay trips?

I hate inducing faults in power amps because one faulty component can
take out many others. Why not upload your manual to eserviceinfo.com,
or link to it if you've found it on the Net, or scan and upload the
relevant section of the diagram to an image hosting site or to your
own web space?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

If I may ask first.

Would too high a voltage for the idling current on one of the channels
be a possible cause?

wrote in message
...
If I may ask first.

Would too high a voltage for the idling current on one of the channels
be a possible cause?


There must be a good reason why the idle current is four times what it
should be. You have suggested elsewhere, that adjusting the pot has
corrected the situation, and appears to have stopped the fault from
occuring. In itself, the idle current being that high, is unlikely to cause
the protect circuit to drop the relay out intermittently. Usually, the only
effect will be that the output transistors on the affected channel, will run
rather hotter than would be considered 'comfortable'. That said, if you had
a 'dicky' pot, it may well be going intermittently effectively o/c, as the
wiper makes and then doesn't. The effect of this could be to shoot the idle
current up way high, which might be enough to trip the protect circuit,
depending on exactly what parameters of the output stages, it is monitoring.

If you have been able to correct the bad idle current to the specified
value, the next thing that you should do is to compare the pot's set
position, or its resistance setting, to the pot on the good channel. If it
is near enough the same, then the most reasonable conclusion is that you did
have a dicky pot, and rotating it has cleared the condition. A further
confirmation of this, would be if the pot had been returned virtually to its
original set point, and the idle current value was now correct. However, if
the pot has had to be rotated a significant distance from where it was
originally set, and is now set at a completely different point / resistance
to the pot on the other channel, then you have a genuine fault, which needs
locating and correcting.

If a preset pot goes intermittent, usually a drop of switch cleaner /
lubricant on the track, and a good scrub from end to end a few times (with
the amp turned off, of course ... ) is enough to produce a long term cure.

Arfa

The right channel pot is around 4.27 kilo-ohms in its current
position. The left channel pot is around 4.28 kilo-ohms.

Putting the right channel pot back to approximately where it was when
the problem existed yields a rating of 5.76 kilo-ohms.

On Mon, 18 Aug 2008 00:56:26 +0100, "Arfa Daily"
put finger to keyboard and composed:

wrote in message
...
If I may ask first.

Would too high a voltage for the idling current on one of the channels
be a possible cause?

If you have been able to correct the bad idle current to the specified
value, the next thing that you should do is to compare the pot's set
position, or its resistance setting, to the pot on the good channel. If it
is near enough the same, then the most reasonable conclusion is that you did
have a dicky pot, and rotating it has cleared the condition.

It stands to reason that rotating the pot fully CCW or CW should not
damage the amp, otherwise not many would have left the factory. If the
trimmer is wired as below, then why not measure the idling
voltage/current at both extremities and verify whether this trips the
relay?

|---|
| |
| V
--|-/\/\/\/\/\---

If neither setting causes the relay to trip, then the problem must lie
elsewhere.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Aug 17, 10:38*pm, Franc Zabkar wrote:
On Mon, 18 Aug 2008 00:56:26 +0100, "Arfa Daily"
put finger to keyboard and composed:

wrote in message
...
If I may ask first.

Would too high a voltage for the idling current on one of the channels
be a possible cause?
If you have been able to correct the bad idle current to the specified
value, the next thing that you should do is to compare the pot's set
position, or its resistance setting, to the pot on the good channel. If it
is near enough the same, then the most reasonable conclusion is that you did
have a dicky pot, and rotating it has cleared the condition.

It stands to reason that rotating the pot fully CCW or CW should not
damage the amp, otherwise not many would have left the factory. If the
trimmer is wired as below, then why not measure the idling
voltage/current at both extremities and verify whether this trips the
relay?

* |---|
* | * |
* | * V
--|-/\/\/\/\/\---

If neither setting causes the relay to trip, then the problem must lie
elsewhere.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Running it at a higher voltage for the idling current does get it to
run hotter. Could the protection be a thermal issue?

On Aug 17, 10:38*pm, Franc Zabkar wrote:
On Mon, 18 Aug 2008 00:56:26 +0100, "Arfa Daily"
put finger to keyboard and composed:

wrote in message
...
If I may ask first.

Would too high a voltage for the idling current on one of the channels
be a possible cause?
If you have been able to correct the bad idle current to the specified
value, the next thing that you should do is to compare the pot's set
position, or its resistance setting, to the pot on the good channel. If it
is near enough the same, then the most reasonable conclusion is that you did
have a dicky pot, and rotating it has cleared the condition.

It stands to reason that rotating the pot fully CCW or CW should not
damage the amp, otherwise not many would have left the factory. If the
trimmer is wired as below, then why not measure the idling
voltage/current at both extremities and verify whether this trips the
relay?

* |---|
* | * |
* | * V
--|-/\/\/\/\/\---

If neither setting causes the relay to trip, then the problem must lie
elsewhere.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Increasing the idling current voltage has started the tripping again.

On Sun, 17 Aug 2008 19:59:52 -0700 (PDT), put
finger to keyboard and composed:

It stands to reason that rotating the pot fully CCW or CW should not
damage the amp, otherwise not many would have left the factory. If the
trimmer is wired as below, then why not measure the idling
voltage/current at both extremities and verify whether this trips the
relay?

* |---|
* | * |
* | * V
--|-/\/\/\/\/\---

If neither setting causes the relay to trip, then the problem must lie
elsewhere.

- Franc Zabkar

Running it at a higher voltage for the idling current does get it to
run hotter. Could the protection be a thermal issue?

If I'm visualising the circuit correctly, then at 30mV the idling
current would be 30mV/0.47R = 60mA. If the supply rails are +/-40V,
then the dissipation in the output transistors would be 80 x 0.06 =
4.8W. At 7.5mV the dissipation would be only 1.2W. I can't imagine
either of these figures would give rise to thermal problems.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Aug 17, 11:24*pm, Franc Zabkar wrote:
On Sun, 17 Aug 2008 19:59:52 -0700 (PDT), put
finger to keyboard and composed:



It stands to reason that rotating the pot fully CCW or CW should not
damage the amp, otherwise not many would have left the factory. If the
trimmer is wired as below, then why not measure the idling
voltage/current at both extremities and verify whether this trips the
relay?

* |---|
* | * |
* | * V
--|-/\/\/\/\/\---

If neither setting causes the relay to trip, then the problem must lie
elsewhere.

- Franc Zabkar

Running it at a higher voltage for the idling current does get it to
run hotter. *Could the protection be a thermal issue?

If I'm visualising the circuit correctly, then at 30mV the idling
current would be 30mV/0.47R = 60mA. If the supply rails are +/-40V,
then the dissipation in the output transistors would be 80 x 0.06 =
4.8W. At 7.5mV the dissipation would be only 1.2W. I can't imagine
either of these figures would give rise to thermal problems.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Would it be okay for me to e-mail you a PDF of the service manual?

On Sun, 17 Aug 2008 20:58:49 -0700 (PDT), put
finger to keyboard and composed:

Would it be okay for me to e-mail you a PDF of the service manual?

Yes. I'll upload it to eserviceinfo for the group, if that's OK,
otherwise I'll put it on my web site.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Aug 18, 12:09*am, Franc Zabkar wrote:
On Sun, 17 Aug 2008 20:58:49 -0700 (PDT), put
finger to keyboard and composed:

Would it be okay for me to e-mail you a PDF of the service manual?

Yes. I'll upload it to eserviceinfo for the group, if that's OK,
otherwise I'll put it on my web site.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Go ahead with whatever you'd like to do with the file.

The manual has been uploaded to you.

However, it has been sent using a different e-mail address than
."

Forgot to follow the directions on your sig regarding sending a
message to your e-mail.

The PDF has been re-sent.

On Sun, 17 Aug 2008 21:11:54 -0700 (PDT), put
finger to keyboard and composed:

On Aug 18, 12:09*am, Franc Zabkar wrote:
On Sun, 17 Aug 2008 20:58:49 -0700 (PDT), put
finger to keyboard and composed:

Would it be okay for me to e-mail you a PDF of the service manual?

Yes. I'll upload it to eserviceinfo for the group, if that's OK,
otherwise I'll put it on my web site.

- Franc Zabkar

Go ahead with whatever you'd like to do with the file.

Here it is:
http://www.eserviceinfo.com/download.php?fileid=37140

Page 25 appears to be the relevant section.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Here it is:http://www.eserviceinfo.com/download.php?fileid=37140

Page 25 appears to be the relevant section.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Here's where it gets hard for me (and shows how much of a noob I am, I
guess). I can't comprehend the schematic diagram.

I mean, I know what some of the symbols mean, but I can't totally
fathom their interaction in the circuit.

On Mon, 18 Aug 2008 15:44:29 +1000, Franc Zabkar
put finger to keyboard and composed:

Here it is:
http://www.eserviceinfo.com/download.php?fileid=37140

Page 25 appears to be the relevant section.

It appears that the protection circuitry is in two parts. Q551 and
Q651 sense the current in the emitter resistors, whereas Q552 and Q553
sense the DC offset at the amplifier outputs. Both protection circuits
trigger the Protect signal at pin 24 of the LM6405G microprocessor via
Q554, and the uP then trips the relay via pin 30.

Disconnecting R556 will disable the DC offset protection, and
disconnecting R553 and R653 will disable the current overload
protection on the left and right channels, respectively. Disconnecting
each of the three resistors one at a time may help narrow down the
source of the problem.

By my reckoning, you would need a DC offset of 2.7V before Q552 would
turn on, and you would need 1.2A in the emitter circuit of Q552 and
Q553 in order for Q551 to turn on. The latter is much higher than your
out-of-spec 60mA idling current.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Mon, 18 Aug 2008 16:34:42 +1000, Franc Zabkar
put finger to keyboard and composed:

By my reckoning, you would need a DC offset of 2.7V before Q552 would
turn on, and you would need 1.2A in the emitter circuit of Q552 and
Q553 in order for Q551 to turn on.

Sorry, that should be Q508 and Q507, not Q552 and Q553.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Aug 18, 2:34*am, Franc Zabkar wrote:
On Mon, 18 Aug 2008 15:44:29 +1000, Franc Zabkar
put finger to keyboard and composed:

Here it is:
http://www.eserviceinfo.com/download.php?fileid=37140

Page 25 appears to be the relevant section.

It appears that the protection circuitry is in two parts. Q551 and
Q651 sense the current in the emitter resistors, whereas Q552 and Q553
sense the DC offset at the amplifier outputs. Both protection circuits
trigger the Protect signal at pin 24 of the LM6405G microprocessor via
Q554, and the uP then trips the relay via pin 30.

Disconnecting R556 will disable the DC offset protection, and
disconnecting R553 and R653 will disable the current overload
protection on the left and right channels, respectively. Disconnecting
each of the three resistors one at a time may help narrow down the
source of the problem.

By my reckoning, you would need a DC offset of 2.7V before Q552 would
turn on, and you would need 1.2A in the emitter circuit of Q552 and
Q553 in order for Q551 to turn on. The latter is much higher than your
out-of-spec 60mA idling current.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

I guess the offset is fixed instead of adjustable. And, I'm guessing
that I'm most likely wrong but, does the idling current adjustment
have any relation to and significant effect with the DC offset?

I don't know why but, after setting the idling current to factory
specs, the amp appears to be stable; the heatsink and transistors
don't run hot and the protection never trips while playing music
through it for 4 hours straight with a pair of Yamaha S55 monitors.
It never worked that well until after the adjustment was done.

And, when setting R607 to where the test lead shows 7.5mV on R ch. and
doing the same for R507 for L ch., the resistance reading were, more
or less, ended up being the same on both pots.

But, when I set R607 to a setting that ends up reading 100mV at the
test point, the heatsink gets kind of toasty and the protection kicks
in within a few minutes.

"Franc Zabkar" wrote in message
...
On Mon, 18 Aug 2008 00:56:26 +0100, "Arfa Daily"
put finger to keyboard and composed:

wrote in message
...
If I may ask first.

Would too high a voltage for the idling current on one of the channels
be a possible cause?

If you have been able to correct the bad idle current to the specified
value, the next thing that you should do is to compare the pot's set
position, or its resistance setting, to the pot on the good channel. If it
is near enough the same, then the most reasonable conclusion is that you
did
have a dicky pot, and rotating it has cleared the condition.

It stands to reason that rotating the pot fully CCW or CW should not
damage the amp, otherwise not many would have left the factory. If the
trimmer is wired as below, then why not measure the idling
voltage/current at both extremities and verify whether this trips the
relay?

|---|
| |
| V
--|-/\/\/\/\/\---

If neither setting causes the relay to trip, then the problem must lie
elsewhere.

- Franc Zabkar
--

Not disputing the "should" Franc, I was just thinking that if the pot was a
bit touchy, then whacking it from one end to the other with it farting
about, might just result in the magic smoke being released from the outputs.
Just being careful, which you, more than most on here, should appreciate is
a sensible thing to do with a DC coupled amp ... d;~}

Arfa

"Franc Zabkar" wrote in message
...
On Mon, 18 Aug 2008 15:44:29 +1000, Franc Zabkar
put finger to keyboard and composed:

Here it is:
http://www.eserviceinfo.com/download.php?fileid=37140

Page 25 appears to be the relevant section.

It appears that the protection circuitry is in two parts. Q551 and
Q651 sense the current in the emitter resistors, whereas Q552 and Q553
sense the DC offset at the amplifier outputs. Both protection circuits
trigger the Protect signal at pin 24 of the LM6405G microprocessor via
Q554, and the uP then trips the relay via pin 30.

Disconnecting R556 will disable the DC offset protection, and
disconnecting R553 and R653 will disable the current overload
protection on the left and right channels, respectively. Disconnecting
each of the three resistors one at a time may help narrow down the
source of the problem.

By my reckoning, you would need a DC offset of 2.7V before Q552 would
turn on, and you would need 1.2A in the emitter circuit of Q552 and
Q553 in order for Q551 to turn on. The latter is much higher than your
out-of-spec 60mA idling current.

- Franc Zabkar
--

OK then, how about this for a scenario. As both pots are now set in about
the same place to get the same idle current, and one of them wasn't before,
it follows that the one which was wrong, had almost certainly been set
wrongly for a long time. This means that the transistors and heatsink on
that channel have been running much hotter than they should have. If it uses
mica washers with heatsink paste, rather than silicone rubber insulators,
the excess heat may have dried the paste out over the years, such that it is
now doing a poor job, and the transistors can get hot enough to start
running away, which creates a large emitter current, which is then sensed,
and causes the shutdown. Even if the insulators are rubber, a close
inspection might reveal that the excess heat has done them no good, and they
have gone hard. Just a thought, as I agree with your thoughts regarding
offdet and current trip points.

Arfa

I don't know why but, after setting the idling current to factory
specs, the amp appears to be stable; the heatsink and transistors
don't run hot and the protection never trips while playing music
through it for 4 hours straight with a pair of Yamaha S55 monitors.
It never worked that well until after the adjustment was done.

There are two ways to go about servicing...

1. Find out exactly what's wrong.

2. Get the device working again.

Most people smart enough to service electronic equipment tend to lean toward
the former. But it's inefficient, and should be reserved for times when it
seems to be really needed.

In your case, it appears that #2 worked (for whatever reason). I would
suppress my curiosity -- your "I don't know why, but..." -- for the time
being and simply enjoy the amplifier.

On Aug 18, 4:59*am, "Arfa Daily" wrote:
"Franc Zabkar" wrote in message

...



On Mon, 18 Aug 2008 15:44:29 +1000, Franc Zabkar
put finger to keyboard and composed:

Here it is:
http://www.eserviceinfo.com/download.php?fileid=37140

Page 25 appears to be the relevant section.

It appears that the protection circuitry is in two parts. Q551 and
Q651 sense the current in the emitter resistors, whereas Q552 and Q553
sense the DC offset at the amplifier outputs. Both protection circuits
trigger the Protect signal at pin 24 of the LM6405G microprocessor via
Q554, and the uP then trips the relay via pin 30.

Disconnecting R556 will disable the DC offset protection, and
disconnecting R553 and R653 will disable the current overload
protection on the left and right channels, respectively. Disconnecting
each of the three resistors one at a time may help narrow down the
source of the problem.

By my reckoning, you would need a DC offset of 2.7V before Q552 would
turn on, and you would need 1.2A in the emitter circuit of Q552 and
Q553 in order for Q551 to turn on. The latter is much higher than your
out-of-spec 60mA idling current.

- Franc Zabkar
--

OK then, how about this for a scenario. As both pots are now set in about
the same place to get the same idle current, and one of them wasn't before,
it follows that the one which was wrong, had almost certainly been set
wrongly for a long time. This means that the transistors and heatsink on
that channel have been running much hotter than they should have. If it uses
mica washers with heatsink paste, rather than silicone rubber insulators,
the excess heat may have dried the paste out over the years, such that it is
now doing a poor job, and the transistors can get hot enough to start
running away, which creates a large emitter current, which is then sensed,
and causes the shutdown. Even if the insulators are rubber, a close
inspection might reveal that the excess heat has done them no good, and they
have gone hard. Just a thought, as I agree with your thoughts regarding
offdet and current trip points.

Arfa

The transistors do, indeed, use mica insulators with heatsink paste.

Having replaced capacitors and redoing solder on the board, I took it
upon myself to clean out the old thermal paste off the transistors,
mica, and heatsink and used fresh paste.

On Aug 18, 7:29*am, "William Sommerwerck"
wrote:
I don't know why but, after setting the idling current to factory
specs, the amp appears to be stable; the heatsink and transistors
don't run hot and the protection never trips while playing music
through it for 4 hours straight with a pair of Yamaha S55 monitors.
It never worked that well until after the adjustment was done.

There are two ways to go about servicing...

1. Find out exactly what's wrong.

2. Get the device working again.

Most people smart enough to service electronic equipment tend to lean toward
the former. But it's inefficient, and should be reserved for times when it
seems to be really needed.

In your case, it appears that #2 worked (for whatever reason). I would
suppress my curiosity -- your "I don't know why, but..." -- for the time
being and simply enjoy the amplifier.

I also tend to lean on the latter.

As the saying goes, if it works then it's not broken. If it's not
broken, don't fix it.

OK then, how about this for a scenario. As both pots are now set in about
the same place to get the same idle current, and one of them wasn't before,
it follows that the one which was wrong, had almost certainly been set
wrongly for a long time.
Arfa

As for how R607 had been set wrong before, I have a very wild guess
about that.

I bought the amp used as a present to a friend, but in the midst of
testing, I found that the receiver had problems with intermittent
power loss. Turned out to have been cold joints on the secondary
power supply block. I think what could've happened was that whoever
owned the thing before I bought it might have tried to "fix" it by
tweaking the potentiometer. What doesn't support this, however, was
that it seems only R607 had been altered. The other pots, such as
R507 and the pots on the preamp circuit do not appear to be a altered
as the tuner and other parts of the preamp section appear to work
properly. Usually, a really bad weekend tech may just tweak anything
indiscriminately until he thinks he fixed it.

I think it makes more sense that R607 has drifted in value somehow.

On Mon, 18 Aug 2008 09:59:21 +0100, "Arfa Daily"
put finger to keyboard and composed:


"Franc Zabkar" wrote in message
.. .
On Mon, 18 Aug 2008 15:44:29 +1000, Franc Zabkar
put finger to keyboard and composed:

Here it is:
http://www.eserviceinfo.com/download.php?fileid=37140

Page 25 appears to be the relevant section.

It appears that the protection circuitry is in two parts. Q551 and
Q651 sense the current in the emitter resistors, whereas Q552 and Q553
sense the DC offset at the amplifier outputs. Both protection circuits
trigger the Protect signal at pin 24 of the LM6405G microprocessor via
Q554, and the uP then trips the relay via pin 30.

Disconnecting R556 will disable the DC offset protection, and
disconnecting R553 and R653 will disable the current overload
protection on the left and right channels, respectively. Disconnecting
each of the three resistors one at a time may help narrow down the
source of the problem.

By my reckoning, you would need a DC offset of 2.7V before Q552 would
turn on, and you would need 1.2A in the emitter circuit of Q552 and
Q553 in order for Q551 to turn on. The latter is much higher than your
out-of-spec 60mA idling current.

- Franc Zabkar
--

OK then, how about this for a scenario. As both pots are now set in about
the same place to get the same idle current, and one of them wasn't before,
it follows that the one which was wrong, had almost certainly been set
wrongly for a long time. This means that the transistors and heatsink on
that channel have been running much hotter than they should have. If it uses
mica washers with heatsink paste, rather than silicone rubber insulators,
the excess heat may have dried the paste out over the years, such that it is
now doing a poor job, and the transistors can get hot enough to start
running away, which creates a large emitter current, which is then sensed,
and causes the shutdown. Even if the insulators are rubber, a close
inspection might reveal that the excess heat has done them no good, and they
have gone hard. Just a thought, as I agree with your thoughts regarding
offdet and current trip points.

Arfa

The OP has stated that the relay trips and closes again, presumably
straight away. Is this consistent with a thermal runaway scenario?

It seems to me that the uP is sensing a fault condition and opening
the relay to disconnect the speakers. But opening the relay achieves
nothing in the case where the amp is unloaded. So if there is a
thermal runaway condition, then surely it will persist even after the
relay is deactivated, in which case the uP should not reactivate it.

BTW, there is an additional 1 ohm resistor in parallel with the two
0.47 ohm emitter resistors, so the misadjusted idling current appears
to have been 120mA, not 60mA as I previously calculated. This current
would result in 10W of dissipation in the output transistor pair
instead of only 2.5W when correctly adjusted. But surely even this
high figure is much less than that generated by the amp when running
under load?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Mon, 18 Aug 2008 09:28:55 +0100, "Arfa Daily"
put finger to keyboard and composed:


"Franc Zabkar" wrote in message
.. .
On Mon, 18 Aug 2008 00:56:26 +0100, "Arfa Daily"
put finger to keyboard and composed:

wrote in message
...
If I may ask first.

Would too high a voltage for the idling current on one of the channels
be a possible cause?

If you have been able to correct the bad idle current to the specified
value, the next thing that you should do is to compare the pot's set
position, or its resistance setting, to the pot on the good channel. If it
is near enough the same, then the most reasonable conclusion is that you
did
have a dicky pot, and rotating it has cleared the condition.

It stands to reason that rotating the pot fully CCW or CW should not
damage the amp, otherwise not many would have left the factory. If the
trimmer is wired as below, then why not measure the idling
voltage/current at both extremities and verify whether this trips the
relay?

|---|
| |
| V
--|-/\/\/\/\/\---

If neither setting causes the relay to trip, then the problem must lie
elsewhere.

- Franc Zabkar
--

Not disputing the "should" Franc, I was just thinking that if the pot was a
bit touchy, then whacking it from one end to the other with it farting
about, might just result in the magic smoke being released from the outputs.
Just being careful, which you, more than most on here, should appreciate is
a sensible thing to do with a DC coupled amp ... d;~}

Arfa

I was following up your suggestion that rotating a dicky pot may have
cured it, in which case returning it to its original condition would
not recreate the original fault. Furthermore, if the pot in the above
case had an intermittently open wiper, then you should be able to
reproduce the same fault by driving the wiper to the far left.

Based on the OP's followup, it appears that the pot itself may not
have been the problem.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Mon, 18 Aug 2008 00:45:38 -0700 (PDT), put
finger to keyboard and composed:

I guess the offset is fixed instead of adjustable. And, I'm guessing
that I'm most likely wrong but, does the idling current adjustment
have any relation to and significant effect with the DC offset?

AIUI, the two are unrelated. The offset is close to zero due to the
negative feedback of R514 which ensures that the voltages on the bases
of the differential pair (Q501) are equal.

I don't know why but, after setting the idling current to factory
specs, the amp appears to be stable; the heatsink and transistors
don't run hot and the protection never trips while playing music
through it for 4 hours straight with a pair of Yamaha S55 monitors.
It never worked that well until after the adjustment was done.

And, when setting R607 to where the test lead shows 7.5mV on R ch. and
doing the same for R507 for L ch., the resistance reading were, more
or less, ended up being the same on both pots.

But, when I set R607 to a setting that ends up reading 100mV at the
test point, the heatsink gets kind of toasty and the protection kicks
in within a few minutes.

By my reckoning, 100mV would result in an idle current of 0.4 amp
which would in turn result in a dissipation of 32W.

Anyway, congratulations on getting your amp working.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

"Franc Zabkar" wrote in message
...
On Mon, 18 Aug 2008 09:28:55 +0100, "Arfa Daily"
put finger to keyboard and composed:


"Franc Zabkar" wrote in message
. ..
On Mon, 18 Aug 2008 00:56:26 +0100, "Arfa Daily"
put finger to keyboard and composed:

wrote in message
...
If I may ask first.

Would too high a voltage for the idling current on one of the channels
be a possible cause?

If you have been able to correct the bad idle current to the specified
value, the next thing that you should do is to compare the pot's set
position, or its resistance setting, to the pot on the good channel. If
it
is near enough the same, then the most reasonable conclusion is that you
did
have a dicky pot, and rotating it has cleared the condition.

It stands to reason that rotating the pot fully CCW or CW should not
damage the amp, otherwise not many would have left the factory. If the
trimmer is wired as below, then why not measure the idling
voltage/current at both extremities and verify whether this trips the
relay?

|---|
| |
| V
--|-/\/\/\/\/\---

If neither setting causes the relay to trip, then the problem must lie
elsewhere.

- Franc Zabkar
--

Not disputing the "should" Franc, I was just thinking that if the pot was
a
bit touchy, then whacking it from one end to the other with it farting
about, might just result in the magic smoke being released from the
outputs.
Just being careful, which you, more than most on here, should appreciate
is
a sensible thing to do with a DC coupled amp ... d;~}

Arfa

I was following up your suggestion that rotating a dicky pot may have
cured it, in which case returning it to its original condition would
not recreate the original fault. Furthermore, if the pot in the above
case had an intermittently open wiper, then you should be able to
reproduce the same fault by driving the wiper to the far left.

Based on the OP's followup, it appears that the pot itself may not
have been the problem.

- Franc Zabkar
--

I think we're talking at cross purposes here Franc. I know what I meant, and
you've known me long enough on here that I think you probably do as well ...

Arfa
Please remove one 'i' from my address when replying by email.