Stetsom EX 6000 power supply mosfets

[barber02]

I don’t believe I’ve ever seen this before.

The drain and source legs of the power supply mosfets have been vaporized but the other side is completely undamaged. Drive signal looks perfect. The drive on the damaged side has a camel hump in the middle of the “on” duty cycle. Interesting.

Each side is running independent transformers.

This is a brand new amp that was installed in a customer’s car by a reputable audio shop.

What could cause this? Shorted transformer maybe? The audio shop said it played for a little while but it was really dragging down the whole system. I bet it was! When I arrived to check it out it would throw up a red LED with 3 blinks. That would be a drained battery. When I got it back to the shop the amp would power up with a blue LED with only B+ and Ground connected. Q10 is shorted. It is an 80v 1A PNP transistor. That may be why the amp powers up without remote turn on voltage.

David

 

[barber02]

Here is another photo with the clamps removed.

 

[Perry Babin]

If it's under warranty, let the owner send it back to the manufacturer. This thing could turn into a boomerang.

If you decide to repair it, push/pull/heat/cool/tap on... everything possible.

It could have been a random failure, a wire strand (I used to see a lot of those) or a failure of another component. Did anything fail in the output stage? Rectifiers?

I used to get a lot of amps with just a few blown outputs and lots of remaining that were good but would never be used again. I saved those for times like this when I needed FETs to test dodgy power supplies in amps but didn't want to risk new FETs.

 

[barber02]

Well. I don’t find any shorts between drain and source pads with the damaged mosfets removed. So I guess the transformer is not shorted to ground.

 

[barber02]

I encouraged them to send the amp back for Warrany repair but they didn’t want to wait that long. They want me to take a look at it instead. I told them I’d see what I could do.

I already see that I will have to order me mosfets for the power supply. They may get it back quicker through me but it won’t be a one or two day turn around.

 

[barber02]

Outputs test good, and rectifiers test good. No broken legs either.

Looks like Q10 failed in a big way.

 

[barber02]

There are no signs of arching against the heat sink either.

 

[Perry Babin]

I don't know how Stetsom works but for some companies, if anyone has tampered with the amp, the warranty is void and the owner is at the mercy of the company. It may cost them hundreds for repair if you can't repair it reliably.

 

[barber02]

I issued that warning to them before I took it with me.