Zapco Z250C4-SL Power supply damaged

[Achim1409]

Hello,
i received a Zapco with damaged Power Supply. Four IRFZ46E are blown. No possible to get any info about this parts, even replacement. Manufacturer has also no sheets anymore.
The Square wave is good. Tried with IRFZ46N, directly blown. Tried only one, again broken. Removed the rectifier, again broken. If i leave disconnected the drain, all is ok.
Checked all resistors and transistors, seems to be ok. I have tried many times to contact Zapco and there resellers, but no answer at all.
I removed U9 (HCF4093) and at the same time a blow away a resistor(R129), which is in line with another resistor (R130). Now i dont know the value of that.
Maybe someone can assist with the Value of R129, and what i can check more from the power supply.

 

[Perry Babin]

Zapco will send diagrams for some of their amps. Keep trying to get a diagram.

Any of the Z46s should work.

You may have a shorted transformer. Is one of the windings darkened?

 

[Achim1409]

Hello Perry,
thanks for the quick reply. The resistor i found back. Was sticking on a capacitor. The trafo has small black windings, but the windings are insulated, so i think there can nothing be happen? The pictures please.

 

[Perry Babin]

Did you look at the waveforms on the gate legs of the PS FETs with the FETs in the circuit?

 

[Achim1409]

Only with the drain disconnected. Should i try with a limiter?

 

[Perry Babin]

Do you have a couple of relatively large (10 ohm, 10w) resistors that you could insert between the drains and the board?

 

[Achim1409]

I just checked the trafo with a lcr meter. All ok. I have 4 pieces 100W 4 Ohm resistors. Maybe enough for that four fets?

 

[Perry Babin]

That would be OK. You only need one FET per bank. With the resistors in series, check the waveforms on the drain side and on the transformer side. Do you get a square wave on any/all?

 

[Achim1409]

The resistors in series with source?

 

[Achim1409]

Ok, here are the waveforms.
1.st Gate
2nd Drain

The Picture with higher voltage ist measured at sec. side trafo between the red marks. The other connections on the trafo have only half voltage.

 

[Perry Babin]

If both drains look the same with the resistors in series, I don't see why it's pulling excessive current with the drains directly in the circuit.

 

[Achim1409]

very strange, now i reasembled complete, and it looks like it works. Only thing, sometimes if i connect the + and - the protection lit is on without remote. If i discharge the capacitors and reconnect, it lit only green.
I will test with speakers now.

 

[Achim1409]

Tested and all ok. Thanks a lot