Help with repair of SX-750

[clk1981]

Unit powers on, tuner meter works, however, the speaker relay never engages. All output transistors test ok, and the unit still doesn't have a relay click with the amp unplugged.

Here are the power supply voltages I was hoping someone could help.

1) -34V
2-7) 0V
8) -34V
9) -.2V
10) -34V
11-15) 0V
16) -51.3V
17) -37V
18) 50V
19-21) 0V
22) 12.8V
23) 32.8V
24) 32.8V

Any help would be greatly appreciated.

 

[zebulon1]

Pins 1 and 4?
Please re-post.

 

[clk1981]

Pins 1 and 4?
Please re-post.

1) -34V
4) 0V

 

[zebulon1]

Pins one and four are the speaker output to the protection relay and the protection circuit. Its seeing a -34v coming out of the left amp. It should be zero like the right amp.
Not knowing what meter you are using or your skills. I would expect a reading of .00xv's, well - less than a volt on pin four if it's operating correctly. Your meter should read below 1 volt.
Your readings indicate a failure in the left amp. It might only be a cold solder connections or loose solder connections due to excessive heat of a component.
The lighting might be a fuse. Fuse 1?

 

[clk1981]

all fuses are good. I'm trying to get the amp board separated from the heatsink now...not much slack in the wires, this is gonna be a pain

 

[vmedia]

Hello - I have similar issues on a sx-750 - High voltages on Pins 1 and 4 - I've rebuilt the Protection relay board and seems to be Power amp board related. I found multiple bad resistors and transistors - apparently a cascade of failures happened at some point in the unit's past. There may be some leanings on this thread: http://audiokarma.org/forums/index....protection-relay-issues.819936/#post-11554444
- I'll continue to keep an eye here as well - thanks!