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/