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Broken Plan B M12 + M14
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Broken Plan B M12 + M14
polyroy
Following on from my 'I broke my turing machine' thread, I'm now looking to fix the Plan B M12 + M14 that got damaged in the process.

Turing machine error was due to having a TL074 and DAC plugged in the wrong way and it seemed it must have shot something across the power rails and messed with the two Plan B modules. Fortunately, nothing else got fried as I had a case full of modules.

The issue with the M12 is if I plug anything into the input or output, it just shuts my case off completely. Not really much else I can report here.

The M14 seems to have noise coming out of the sum outputs even when nothing is plugged in. The output polarity pot affects the strength of noise and the leds correspond with the positive and negative voltages, but there's just constant noise present at the output.

Although my soldering skills are good enough to fix it myself, my diagnostics aren't. This will be the first time using a multimeter outside of measuring resistance/capacitance/continuity etc, so any pointers on where to look at and what to probe would be very welcome. I've attached photos of the boards and whilst I've only got one M14, I have another M12 I can use as a reference.

M12



M14

Navs
If you haven't already, you know the doctor to contact ...

Else, 'shutting off the case immediately' sounds like a short circuit in the M12. Can you check that first? Other, easy steps would be swapping the opamps. Transistors will mean soldering, but they would be worth checking.

On the M14 mixer, I'd have to look at Tim's page again, but if it's the VCA chip, there are replacement clones available these days, which means you will be able to replace that part.

Good luck!
polyroy
Apologies for late reply! May have to drop Tim a line if I can't figure it out from the more simple tests. Will have to build a bench PSU going forward, major lesson learned from this debacle!

No noticeable short circuits on the M12, worked fine for ages before I plugged the Turing Machine in with the backwards chips. Will check the op amps on both modules with a multimeter and can order more if it's them that's busted. I know they're not super complex circuits (especially the M12), just my first time doing diagnostics and kind of shitting it a bit.
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