Active speaker SMPS problem

[Rutherberg]

Hello,

Again, I have a hard time to diagnose an SMPS in an active speaker.
It is a Behringer Eurolive B912 NEO, schematic is attached.

It came with a power problem, last time it was used, it was powered by a diesel generator, so AC source wasn't very stable.
Last time powered on (with proper power source), I heard a loud explosion inside, D7 and D9 are exploded and jumper J1 blowed.

Bridge D63 is not shorted, T1 and T5 neither.

Could you help me find the problem ? What could be potential problems ?

Thanks in advance !

[IanMacdonald]

D7 and D9 are overvoltage protection for the reservoir capacitors. They most likely failed due to excessive input voltage. Though, they could also have failed due to an incorrect mains voltage selection, or perhaps due to very asymmetric loading of the rectifier such that one cap has more than 200v across it, the other a lot less. 

J1 would only be connected if on a 120v supply. It causes the rectifier to act as a voltage doubler instead of as a bridge.

Basically, when faced with this kind of repair you need an isolating transformer (and I mean isolating, not center tap earth as are used on building sites) and a variac or dim bulb tester. If you have nothing else to hand the dim bulb tester is easy to make up.

Main point to note is that you cannot do 'scope checks on this kind of equipment without an isolating transformer.

[b_force]

Main point to note is that you cannot do 'scope checks on this kind of equipment without an isolating transformer.

I don't see why? 
Yes, it's a bridged amp, but simply build with two mono amps with an inverted signal.
So there is nothing floating or something.

OR do you mean to gradually higher the input voltage to see what's wrong?
(like using a variac or variable transformer).
In that case, yes that's the way to go.

Generators are a pain for amplifiers.
I can show one from my work were a part of the PCB is just totally gone (as in REALLY gone)

Pretty classic design btw, with the IRS20955.
Only a bit weird with a TDA7293 (pissing away energy)