Onkyo TX-82 stereo receiver fault. Suggest possible solutio

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?

 

On Aug 16, 8:34 pm, "DaveM" <masondg4...@comcast99.net> wrote:

laseranddvd...@aol.com> wrote in message

news:536c6a0b-431d-42e5-a82a-9a4a051579d5@p25g2000hsf.googlegroups.com...



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.

 

[Franc Zabkar]

On Sat, 16 Aug 2008 15:45:37 -0700 (PDT), laseranddvdfan@aol.com 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.

 

On Aug 16, 8:34 pm, "DaveM" <masondg4...@comcast99.net> wrote:

laseranddvd...@aol.com> wrote in message

news:536c6a0b-431d-42e5-a82a-9a4a051579d5@p25g2000hsf.googlegroups.com...



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?

 

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.

 

[Franc Zabkar]

On Sat, 16 Aug 2008 23:36:58 -0700 (PDT), laseranddvdfan@aol.com 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?

 

[Franc Zabkar]

On Mon, 18 Aug 2008 00:56:26 +0100, "Arfa Daily"
<arfa.daily@ntlworld.com> put finger to keyboard and composed:

laseranddvdfan@aol.com> wrote in message
news:7956f71e-9fee-41a7-b61a-86a80a6722f9@m3g2000hsc.googlegroups.com...
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.

 

[Franc Zabkar]

On Sun, 17 Aug 2008 19:59:52 -0700 (PDT), laseranddvdfan@aol.com 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.

 

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 Aug 17, 10:38 pm, Franc Zabkar <fzab...@iinternode.on.net> wrote:

On Mon, 18 Aug 2008 00:56:26 +0100, "Arfa Daily"
arfa.da...@ntlworld.com> put finger to keyboard and composed:

laseranddvd...@aol.com> wrote in message
news:7956f71e-9fee-41a7-b61a-86a80a6722f9@m3g2000hsc.googlegroups.com...
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 <fzab...@iinternode.on.net> wrote:

On Mon, 18 Aug 2008 00:56:26 +0100, "Arfa Daily"
arfa.da...@ntlworld.com> put finger to keyboard and composed:

laseranddvd...@aol.com> wrote in message
news:7956f71e-9fee-41a7-b61a-86a80a6722f9@m3g2000hsc.googlegroups.com...
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.

 

[Franc Zabkar]

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

On Aug 18, 12:09 am, Franc Zabkar <fzab...@iinternode.on.net> wrote:
On Sun, 17 Aug 2008 20:58:49 -0700 (PDT), laseranddvd...@aol.com 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.

 

On Aug 17, 11:24 pm, Franc Zabkar <fzab...@iinternode.on.net> wrote:

On Sun, 17 Aug 2008 19:59:52 -0700 (PDT), laseranddvd...@aol.com 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?

 

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.

 

[Franc Zabkar]

On Mon, 18 Aug 2008 09:59:21 +0100, "Arfa Daily"
<arfa.daily@ntlworld.com> put finger to keyboard and composed:

"Franc Zabkar" <fzabkar@iinternode.on.net> wrote in message
news:gu5ia49k5eanhubb6spbirvjemrvpi5bei@4ax.com...
On Mon, 18 Aug 2008 15:44:29 +1000, Franc Zabkar
fzabkar@iinternode.on.net> 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.

 

[Franc Zabkar]

On Mon, 18 Aug 2008 09:28:55 +0100, "Arfa Daily"
<arfa.daily@ntlworld.com> put finger to keyboard and composed:

"Franc Zabkar" <fzabkar@iinternode.on.net> wrote in message
news:ialha459fbe4dm40e780iq267kd3ov0soa@4ax.com...
On Mon, 18 Aug 2008 00:56:26 +0100, "Arfa Daily"
arfa.daily@ntlworld.com> put finger to keyboard and composed:

laseranddvdfan@aol.com> wrote in message
news:7956f71e-9fee-41a7-b61a-86a80a6722f9@m3g2000hsc.googlegroups.com...
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.

 

[Franc Zabkar]

On Mon, 18 Aug 2008 00:45:38 -0700 (PDT), laseranddvdfan@aol.com 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.

 

Anyway, congratulations on getting your amp working.

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

Thanks, but it concerns me that, since I can't understand why, then I
may be missing something, such as a condition where this could be a
temporary fix in the end.

 

I understand exactly what you're talking about, but it simply isn't
productive. There are better ways to use your mental energy.

Pots (or the circuits they regulate) can and do drift. I've bought several
of the original Sony FM Walkman, and all have required the stereo sync pot
to be readjusted (by ear is sufficient) before the tuner would switch to
stereo.

Thanks for the reassurance.