SMPS Repair - Allen and Heath 6 Channel Mixer

[batou]

Hi, can anyone help me understand whats wrong with this SMPS? U2 is a TNY287. U3 and U4 are 7812 and 7912 regs respectively. U4 had a small hole / burn marks and has been replaced. D7 is an SB1100 schottky that was shorted - also replaced. Other diodes test ok in-circuit. Main filter caps test OK and are sittng at 330v. Output voltages are as follows:

P1: 37.1v
P8: 3.6v
P12: -24v
P9: -12v

Any tips/pointers of what it could be, or what to test next are greatly appreciated!

[KevinA]

No idea what model you have, but this is the manual I did for my techs ten years ago for the ZED series, it may provide a few clues for you.

[batou]

I think its actually doing whats its meant to do! The point I was taking as ground isn't ground relative to the regs. D'oh.

Thanks for the PDF!

[Mark Lowe]

Have same mixer, had same fault only the +12v reg was fine. Replaced D7 and everything ok. Cheers.
- Update, intermittently power fail, USB disconnects. Replaced both 7812, 7912 regs and both D3 & D7, now operates ok but then again shuts down after far greater time, up to an hour, spikes audio but remains powered up.
Voltages to main control board 12v, -12v & 32v
Mixer is only just out of warranty and barely used. Disappointing A&H.