Soundcraftsmen MA5002 Voltage Rails down

[MNRepair]

rectifier diodes next in line are measuring how much DC voltage? View attachment 3827760

Rectifiers only have 0.4VDC (forward voltage of the diodes?)

 

[MNRepair]

Does the protect LED turn on and then off after a few seconds when you turn it on? If so, check voltage at pin 1 of U2. It should go from 0V to about 1.8-2V when it's supposed to turn on the triac.

The protect LED does not turn on at all, only lights that come up are the meter llights.

Pin1 of U2 is 9VDC.

 

[Racingh11]

The protect LED does not turn on at all, only lights that come up are the meter llights.

Pin1 of U2 is 9VDC.

That's not normal. Seems like the LED is open on the optocoupler, but also the protect LED should come on. Because the power that turns on the optocoupler, is the same power that turns the protect LED off, and it comes from pin 4 of U1. I have seem replacement U2 ICs not contact the pins on the socket on certain styles. Check voltage on U2 pin 2, should be ground, will be high if that pin is not making contact. Happened more than once. I replace the stock 8 pin with a better 6 pin. Pin 4 of U1 should start out near 0V when powered up, then close to 12V after a few seconds.