Allen and Heath PA CP power amp

"Gareth Magennis"

** You might have swapped the N and P channel mosfets.

FFS !!!

Always power up gradually with a variac and small value rail fuses after repairing a blown up power amplifier.

Monitor the AC supply current OR the DC supply current at the same time too.

** Yep.

Now answer my questions:

Are the DC rail fuses connected as shown in the schem ?

Are there really NO zeners on the mosfet gates ?

... Phil

The devices were the right way round. I marked the heatsink before removing the originals.
The amp was carefully powered up on a variac and 100W series lightbulb. Relays clicked and no limit LED this time on front panel.
Prior to that I had used a +-30v bench supply on the PCB, no current draw at all.
With lightbulb disabled, amp then blew a few seconds after power up. Yes, stupidly I did not fit 500mA fuses as I usually do. That'll teach me not to be so cocky. Doh!

The original fuses were intact and did NOT blow on power up - just that sides limit LED lit. They are blown now.

No Mosfet resistors are burnt this time, the Mosfets again read good on my tester, but that seemingly is meaningless.

I will check out your other questions later.

Cheers,

Gareth.

DC rails are as per the schematic.

There are no gate zeners.

Cheers,

Gareth.