PC2602M Protection Issue

Heddarn

New Member
It started with some relay cutoffs while playing music.
A week ago it took about 5-90 minutes for the protection relay to release.

Im in need of ideas and suggestions what to do.
Channel A heatsink get´s around 40 Celsius and channel B stays cool.

I have measured the powerbank and it delivers enough juice.
One odd thing i have noticed with the cutoff relay is that both poles on the coil got a positive 30V while the protection indicator is on.

I have compared the transistors from cannel A and B and could not find any anomalies.

Sry for my bad english, english lessons were not my cup of tea 20 years ago :)
 
One odd thing i have noticed with the cutoff relayis that both poles on the coil got a positive 30V while the protection indicator is on.
Normal for a denergized relay.
Need to check the DC offset and bias adjustment for both the "cooler and warmer" amplifier assemblies. To much offset may trip the protect circuit.To much bias causes excessive heat - excessive heat may cause the protect circuit to trip if the protect circuit has thermal cutoff provisions.
 
Can somebody provide me info on DC Offset and Bias Adjustment for this model?
Can´t find anything about that in the service manual.

Dunno if that´s even possible without a oscilloscope.
I´ve seen some posts about that earlier and that required an oscilloscope.
 
Not in the service manual..:scratch2: Strange! Offset can be monitored at the speaker connection. Not sure if this model uses a DC servo circuit to control the offset.That would explain no offset adjustment. Do you have a
idle current adjustment, DC balance adjustment,DC zero adjustment in the manual?
 
I got a bunch of nothings, only some notes but no currents.
The only service manual i have, seems to be a bit older than my amp, some components in the manual does not match the components in my amp but the boards are a complete match.
 
Have you contacted Yamaha service directly, they are known to be very help full
with additional documentation.
 
No, i have not contacted them yet. Since it´s summer and my friends keeps me occupied whit boring summer stuff :)
I know they are helpful, i have contacted them before when my other amp got the idea to play smoke machine instead of AC / DC :)
I was hoping that someone here had similar problems before and had a simple solution.
I have not've worked with electronics for very long so I'm still pretty green.
But I should contact Yamaha.
 
I have that amp, let me check my service manual to see if there's anything about bias adjustment.
 
That's weird, no bias information at all. I hope I don't have to mess with mine.:sigh:

I did find out that the DC threshold for the protection circuit is 2 volts at the outputs, so you have at least that much voltage likely that's keeping your's in protection.

Sorry, wish I had more information to help you with.
 
That's weird, no bias information at all. I hope I don't have to mess with mine.:sigh:

I did find out that the DC threshold for the protection circuit is 2 volts at the outputs, so you have at least that much voltage likely that's keeping your's in protection.

Sorry, wish I had more information to help you with.

Or...a flaky protect circuit component.But the fact that one amp gets much warmer than the other sorta weighs into the equation.
 
Measure the bias voltage across one of the emitter resistors of the cooler channel and compare it to the warmer one.Offset can be measured at the speaker connections of both channels until the amplifier goes into protect.
Offset can be measured at the speaker connections of both channels until the amplifier goes into protect.
This will at least give you a clue if you measure any substantial DC. Ideally the offset should be very close to 0.0 volts but probably be around +/- 10 mv.
 
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Well said. The master has spoken.:thmbsp:

One day, if we live long enough, I will talk to you about "refreshing" both of my Yamaha amps.:wave:
 
Sry for taking so long to reply, just got home from vacation.
Started up the amp and it no longer release the protection on startup so that makes it a bit hard to measure the output terminals.
Gonna give it some time.
I have noticed a cap that needs replacement in one of the amps, gonna check if i have a replacement. Not yet bursted but a little bit bold at the top. I feel a bit stupid not noticed that before... "C203" on PAB
Got 3.8mV on both amps output terminals while in protection. Im gonna measure the resistors later this evening. tnx for all support :)

Did a quick measure of the resistors:
On PAA i got 0.0V on both poles and on PAB i got 92V on both poles.
 
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Got 3.8mV on both amps output terminals while in protection
Where exactly did you measure this at? The speaker binding posts? If so,you can only get a valid measurement when " not in protect mode".If it is in" protect mode", the relay(s) isolates the speaker posts from the actual amplifier output.
 
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Now i have desoldered the outputs and drivers from both PAA and PAB and got a complete match on the components. No shorts or bridges.
Took a few pictures.

http://www.audiokarma.org/forums/album.php?albumid=1758&pictureid=11444
http://www.audiokarma.org/forums/album.php?albumid=1758&pictureid=11443
http://www.audiokarma.org/forums/album.php?albumid=1758&pictureid=11442

I can set up some high resolution images on one of my servers if needed.
Im about to give up and put it in a box for a rainy day.
I got a theory, that the 92V im getting from the emiter resistors is fed from the protection cercuit itself and im barking up the wrong tree.
 
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What i realy want to know is the voltage value from the psu.
I dont have any values to refer to.

I recall i measured around 90V on a wire at CN206 i PAB that comes from PSU CN402
 
Now i have put all things back in the chassi and it works!.
Measured PAB the first thing i did and then it was 0V on the emiters.
then i turned it off then on, and now back to the same story,, starts up with 90V on the emiters in PAB and protection indicating.
 
90 vdc on the emitters.Not good. Usually this is caused by a shorted output or driver transistor.Or one of the aforementioned is being biased on and holding the emitter(s) at rail voltage. Your going to need to acquire a schematic.
 
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