Troubleshoot Electronics

[2mbb]

I'm not sure where to post this. I need some guidance or links to resources for troubleshooting an electronic board that started blowing fuses. This is from a Branson ultrasonic cleaner. I got the thing used and for free. It was tripping the GFI circuit at my friends house when he gave it to me, but it was working before for me (no GFI circuits at my house!). But now it just blows the on board fuse when I turn the power on. I found a couple of weak solder joints when I was taking it apart, so I resoldered them, but it's still blowing the fuse. Unfortunately, I don't have the wiring diagram--can't find one on the internet either.

Any thoughts where to start?

Anybody have some good web resources for identifying components and testing.

Oh, I have a multi-meter, but no other specialized test equipment.

Thanks.

 

[2mbb]

I was able to track down a schematic. It's the F-3A fuse that is blowing.

I don't have the heater or timer options, nor do I have the B-8200 interconnect (whatever that is).

 

[se2000]

They use a loose transformer for a lot of ultrasonics, that will blow a gfci. But your problem is real. did you ohm out all the components? a bad transformer will be the hardest to tell. But it should not be a dead short. I am betting that is what happened. It got old and the insulation broke down.
Ohm away and let us know what you find.

 

[2mbb]

Thanks. I put an ohm meter on the component while installed on the board, but seemed to get confounding results--most of the diodes showed connectivity in both directions, etc. I think I need to remove some or all of the components to eliminate circuit bypasses.

While the wiring diagram and board show pins for an external transformer, this unit does not have one. It's basically what you see in the first picture, plus the on/off switch, 110V ac input and four piezo patches on the tank.

 

[se2000]

I would lift the transistors, most likely to be shorted. next the transformers.