On 03/11/2014 15:40, Gareth Magennis wrote:
"N_Cook" wrote in message
...
Putting my deer-stalker hat on. Someone had been inside to replace the
fuse. Left out some of the screws, including one self-tap that holds the
IEC. If that one was previously missing and the IEC just "held" by the
remaining one next to the TOP heatsink,loosened by repeated IEC insertions
AND the sillypad was punctured or close to puncturing. Then the drummer
tripped over the lead, IEC twisted and the IEC holding screw touched the
heatsink, as it is long enough, then blown TOP244, but about 4mm gap to
swing across to do so. But as there are no pcb standoffs to chassis in
that area, relying on the IEC screws to chassis, then perhaps the whole
pcb being tilted in a downwards sense, by drummer standing on the lead,
and then only that arctan(2/20) 2mm gap for heatsink to contact chassis.




Seems Peavey these days have turned all Chinese, they always used to be very
conventional and pretty reliable really..

I have a small mixer here now, a PV8 USB. It uses an 8 pin DIL JRC2360
DC/DC converter, I think to generate the 48v phantom from the 15v DC input.

Anyway its busted, and an easy diagnosis because a bench supply input heats
up this chip nicely. (The supplied SMPS wall wart trips out).
In the old days, a fault with the phantomn power part of the PSU was very
unlikely to render the whole mixer dead.

Cuh.




Gareth.



Nothing obviously loading the ps (cold) will power up replacement
tomorrow, presumably 48V and raw +/-15V as only one vr on the smps pcb,
component side of the big board not seen.
Looking a bit deeper into TOP24* datasheet. This PV14 has the 4 central
pins connected together, 3 terminal device, which is over-voltage
disabled mode.
So what happens in mains dropout and reconnection scenario, as with
drummer tripping over the mains lead and auto-restart on what it
erroneously determines to be low mains voltage setting. Would
probalistically be the same for those floppy 4-way plastic distribution
sockets, breaking and making, blowing the supply, if this is a potential
failure mode. 240V in the UK.