Faulty MTX 500D

[Chuppster]

I pulled the output transistors and the LED lights up. I read 12v across terminals.

 

[Perry Babin]

Measure the DC voltage from pin 4 (black probe) to pin 8 (red probe) for all of the op-amps. Do you read ~35v DC (~±18v to ground)?

 

[Chuppster]

All 5 read 3 Volts.

 

[Perry Babin]

Post the DC voltage on all legs of the regulator transistors.

 

[Chuppster]

Which transistors are those? The power transistors?

 

[Perry Babin]

The two transistors on each side of the resistors that were burned in one of your previous photos.

 

[Chuppster]

Q3/62 - Leg 1: -8.5 Leg 2: -9.3 Leg 3: -8.9
Q2/61 - Leg 1: -5 Leg 2: 18 Leg 3: 25

 

[Perry Babin]

You'll need to replace the resistors and remove those 4 transistors and then post the numbers again. The original resistor value was 150 ohms but any resistor 150-1000 ohms should allow you to test further.

 

[Chuppster]

Here's what I have. So, I need to put resistors in the board and leave the transistors out?
https://drive.google.com/file/d/0B50P1QWuuYzcR1FTbllmNFdpbm8/edit?usp=sharing

Yes, some of the traces have been pulled out of the board, however I replace them with copper cable if necessary.

 

[Perry Babin]

Yes. Install the resistors but not the transistors.

Clean the board so that you can be sure that there are no shorted pads/traces.

 

[Chuppster]

Many traces have been pulled from the board and disconnected at their endpoints. Could I get the circuit diagram so I can know what connects where?

 

[Perry Babin]

I don't have a schematic diagram for this amp. If you clean it up, you should be able to tell where each trace goes.

I think the resistors go to the collectors of the regulator transistors. The emitters of the regulator transistors connect to the op-amps. The bases of the regulator transistors connect to the zener diodes. You can verify these with a multimeter.

 

[Chuppster]

I am having trouble finding what pin 3 of Q63 should go to.

 

[Perry Babin]

See attached.