Help Fixing a MTX Tunder 302

[Frycztech]

Here is the area.

 

[Perry Babin]

I'm sorry but I just don't have enough information on this amp (or any one similar). I looked around in the shop but I don't have one to use as a guide.

 

[Frycztech]

Is there anything else I should try? Should I try another cap or is it not worth it?

 

[Perry Babin]

If you are 100% sure that the polarity was correct, there isn't a reason to install another cap. If there was no excessive DC applied to the cap, there must be AC present. You'd likely need a scope to confirm.

 

[Frycztech]

Ok I dont have a scope and when i asked mtx they said they wont give out a schematic. So it looks like ill just put it back together

 

[Frycztech]

I checked the AC voltage with a meter and got 25.9VAC. I dont know if that helps at all or not.

 

[Perry Babin]

Are any of the diodes in that area shorted?

 

[Frycztech]

The 2 diodes on the right of the first pic give me a short beep when I test them but arent showing there open at all. Is that normal?

 

[Perry Babin]

I don't know your meter but a short beep is likely OK. A steady beep would indicate that there could be a shorted diode.

Post a good quality photo of the bottom of the board near the diode. Mark the legs of the diode to show its location.

 

[Frycztech]

Sorry for the delay. The first pic is the 2 pins of the cap that keeps blowing. The 2nd pic is the one of the diodes.

 

[Perry Babin]

It looks like the cap may be part of a voltage doubler circuit. Anything that's loading that circuit (anything beyond that cap) could be causing the cap to fail. The cap may be part of a circuit like the one below. Your cap would correspond to C771 or C772.

 

[Frycztech]

So what would the next step be to troubleshoot?

 

[Perry Babin]

Check all components that the cap connects to.

 

[Frycztech]

Dose it matter ehat leg i Start with? One leg goes to the coil right by it and the other goes to the first diode and resistor.

 

[Perry Babin]

The problem is unlikely to be on the transformer (coil) side.

 

[Frycztech]

I started to look at getting this amp finished and I popped out and tested the first diode and i belive its bad. It has BYW 100 200 C019 on the case. I bealive this is it:
BYW100-200 STMicroelectronics | Mouser

Would this be a good replacement?
STTH1R02Q STMicroelectronics | Mouser

 

[Perry Babin]

That looks OK. What makes you think it's defective?

 

[Frycztech]

It's reading shorted in both directions.

 

[Perry Babin]

If it's reading that out of the circuit, there's no doubt that it's defective.

 

[Frycztech]

Yes it is.