Hi All,

I've been getting on ok with my Pentas (only had them a couple of months) and have successfully repaired one of the amps. The other failed last night. Was working perfectly, then suddenly there was a loud buzz sound and it stopped working. I didn't realise, but it had gone into protection mode.

Now when troubleshooting it, it won't stay out of protection mode, so it's a bit hard to measure voltages, etc.!

Prior to the fault, I replaced the op-amp with a Burr-Brown one. Lovely. I also replaced all the electrolytic capacitors that were in the signal path with high quality poly (I think - can't remember exactly).

I also recapped the crossovers.

Since the fault occurred I have recapped the rest of the board (except the power supply region, which seems ok). None of the capacitors I removed was faulty. I have also temporarily replaced the NTC (temp sensor) resistor with a 330K resistor. I also tried replacing the op-amp with the original.

So far, nothing has made any difference. Amp goes straight into protection mode.

I'd appreciate any thoughts anyone might have! What would the loud buzz indicate? Do I have failed output transistor(s)??

Thanks,

Andrew