On 22/06/2016 18:58, Gareth Magennis wrote:


"N_Cook" wrote in message ...

With just the main PA rail AC supply connected, no load,sometimes at
switch on will draw sustained 2 amp , so quickly switched off.
At 50% mains , sustained 1 amp draw until switched off.
Mains Tx ok on its own.
DVM-D cold testing of PA devices and bridge rect etc check out reasonable.
What to look for cold initially?
I may try hot test again with the speaker output pcb disconnected as
speaker protector thtristors on there.
Initially one output channel failed soon after power up, which could be
sp prot failure presumably, mains fuse did not blow though but that
=500W would be going somewhere it shouldn't.
Perhaps another 50% mains half second try out and see if a thyristor is
hot.








Peavey typically put a Triac circuit on the speaker outputs to short and
blow the amp/fuses instead of the speakers should it go DC.

I tend to use a dual bench current limited supply, and remove the Triac
when troubleshooting.
Mine only goes to +-30v, but I've never found that a problem, it will
still safely find a short etc.



Gareth.

What seems odd about this , is it is intermittant.
Sometimes it would power up properly , even at 100% mains, ie nothing is
permanently defunct.
I'll have a closer look at solder joints, if a bias is dropping out.