Orion 250 hcca gen 2 power supply blown

Hello,

I have a gen 2 Orion 250 hcca that appears to need extensive power supply repairs, at least.

It appears that one side of the clamped transistors (FETs I think for this amp) are gone (several show a short), and perhaps several on the other side. The board shows some related damage, but looks to be usable. I think rectifiers are in this area too and may need to be replaced.

The small transformer standing on end is burnt up, I will probably have to order and wind a new one.

Several fluid electrolytic caps are obviously in bad shape. I already have all such caps for this amp on hand.

I do have access to several working versions of this amp, which should help.

Questions are:

1.) How best to start with repair.

2.) Replacement part suggestions for FETs, rectifiers, transformer core/winding, etc. I suppose I may be able to figure this out but any suggestions are appreciated.

Thanks in advance for any help or feedback.
 

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Check all of the PS FETs from the gate to the other two legs and remove the ones that are shorted. See if it will power up.

OK, thank you.

Do you have much experience repairing amps?

Some, but not much. I am an EE though, and equipped with plenty of patience. Working on amps is a hobby to me. This amp was a give away, and I am not interested in paying anyone to repair it.
 
I removed the burnt FETs on one side, several caps, and the smaller inductor standing on end in the picture that is charred.

I cleaned the board and it seems to not be damaged significantly.

I want to replace the small inductor. It is seven-wires, five turns, I can determine the wire gauge and the core dimensions.

The question is what is the correct core to use? There are several in the correct size range that vary by inductance factor. Anywhere from about 2 uH to 10 uH. This number is proportional to the actual inductance. Should I select the largest available, does it matter? Is epoxy coated OK?

Thank you for any help!
 
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Are you replacing for cosmetic reasons alone?

Do you have an inductance meter? If not, ie there a local shop that could measure the inductance?

If the core itself isn't charred, it likely is perfectly fine.

If the core isn't damaged but the windings are shorted, rewind with the same number of turns (any insulated wire will be OK) and measure the inductance.
 
I guess I could build a simple charging circuit, measure the time constant, then calculate the inductance.
But I guess this is impractical for the expected inductance.

And that would involve removing a part from a good amp, and I would be assuming they are indeed the same (the working amps are the same "generation" and layout, but possibly a different revision.)
 
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Based on typical inductance factors and it being 5 turns, I expect it to be in the 50 uF to 250 uF range, approximately. Going to 7 turns would double the result, since inductance is proportional to turns squared and 7 squared is about twice 5 squared.

If I had a function generator I could measure the corner frequency when using it in a first order low-pass and calculate inductance from the result. This is probably the easiest way to go without a meter.
 
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It does share a connection with the pair of large 3300uF caps shown, which themselves are probably for supply filtering. I would think that would make the actual value not too critical, but again can't be sure.

It connects B+ to the positive terminal of both caps. As if to increase the filtering order perhaps as you suggest. So that would definitely be low pass, which makes me think larger is better?
 
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Thank you for your help Perry.

The only visibly damaged parts were all 9 FETs on one side (NDP 7060), that inductor, and several caps. I was planning to replace all of that, then make some non-powered DMM measurements (using the working amps for some comparison) to try to determine if there is any other damage, and if it is ready to test.
 
I've been checking over the amp, and a couple of outputs look suspicious, and possibly smell suspicious. They are on the same side that failed in the power supply. I am not, however, reading any shorts.
 

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Yes I suppose. The whole thing still smells a little. I had myself convinced those exact transistors smell, but when I pick up the burnt FETs I removed and smell them there is really only a weak smell if anything. So I will leave them in for now. I can't find anything else obviously wrong but the supply filter components and the FETs on one side.