Yamaha M-50 Protect Mode

[Audi2014]

Hello everyone,
I just acquired a Yamaha M-50 stuck in protection mode. Here is what I have found so far. No burnt components on all boards.
Tested DC Voltage on the output transistors on both sides of the board per the service manual and seem to test fine.I plan on
removing output transistors from the unit just to verify that they are functional. Has anyone in this group had to pleasure of working
on one of these units?
Thanks,
Audi2014

 

[Netlist]

Me, but ages ago and my memory has faded.
Nice sounding amps and a very cool front.
In general I would check for worn solder joints.
Look for DC before the relay and compare with the other channel, if that still works.
I'll have a look at the manual for I don't remember if each channel has his own protection circuit.
Can you post the Service Manual?

Hugo

 

[madis64]

I plan on removing output transistors from the unit...

Why would you do that?
It would be wiser to measure DC on the amplifier output (before the relays) and also power rail voltages for a start.
There may be fault in the amplifier but also the speaker protection circuit may give you false alarms.
Replacing all lytics in the speaker protection circuit would also not hurt.

 

[madis64]

Can you post the Service Manual?

The one at Hifiengine has the schematics.

 

[Netlist]

I know, but I'm a bit lazy ATM. 😉
I'll look tomorrow.

Hugo

 

[Netlist]

Thanks, I advice to read it before attempting the repair.
Also, as madis said, no need to take the outputs out.

Hugo

 

[Netlist]

Pages are missing in the manual.
Here's a better one:

Edit: Audi2014, I took the freedom to remove yours to avoid confusion.

Hugo

 

[Audi2014]

Thank you.This one has a lot more info than the one I found. Thank you very much!