DD Z2B exploding output transistors

[yoppi]

hi.

I am working on a DD Z2B in its output section. After it arrived at the workshop, I replaced the 28x 24n50f, 28x 33ohm gate resistors, irs2184s, 4x tc4452vat, 18v zener diodes, 7812 2A, checked resistors and everything was ok.
I started the amp and it blew up one side almost completely.
What could be causing this problem?

thank you.

 

[Perry Babin]

Is the mute/delay circuit functioning as it should?

 

[yoppi]

I checked the J111 transistor that belongs to SD and the MUTE circuit, all the components seem to be fine.

I have also tried to turn on only the output board with lower external voltages (+/- 24v) but I think it has a protection circuit against low rail voltage (image attached) that I don't know how I should "fool" it and be able to start safely....

 

[Perry Babin]

When you used low voltage, did you remove the rectifiers and power up the board normally with the only difference being that the output rails had only ±24v?

 

[yoppi]

That's right, but turn it on for protection.

 

[Perry Babin]

With ±24, do you get the 12v for the low-side drive?

What's the DCV on the SD pin of the driver IC?

At this point, which parts are out of the board?

 

[yoppi]

Yes, I power 12v with another external source (I'm lucky to have 6 power supplies in the workshop) I have not checked the SD voltage, since, when I checked J111 that it was OK, I did not give it any more importance. When I performed those tests, everything was in place, never part outside the PCB. but I was never able to measure PWN on the output because the amplifier was in protection due to the rail undervoltage protection circuit.

 

[Perry Babin]

You shouldn't need to supply 12v to the low-side supply on the driver IC.

It had blown output FETs. Did you replace them all?

 

[yoppi]

Yeah. They are all new. from a batch that I have already used in other amplifiers and they work perfectly.

 

[Perry Babin]

Do you have the low-side 12v without an external supply?

What protection do you see that's shutting down the output under low-voltage?

 

[yoppi]

I have not performed that verification. I'm going to disassemble the amplifier again and put new parts back in. I will do checks and report.