Broken Plan B M12 + M14

From circuitbending to homebrew stompboxes & synths, keep the DIY spirit alive!

Moderators: luketeaford, Joe., lisa, Kent

Post Reply
polyroy
Ambient Wiggler
Posts: 3823
Joined: Wed Mar 31, 2010 6:01 pm

Broken Plan B M12 + M14

Post by polyroy » Fri Sep 13, 2019 4:28 pm

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
Image
Image

M14
Image
Image

User avatar
Navs
Super Deluxe Wiggler
Posts: 4185
Joined: Fri Sep 18, 2009 3:49 am
Location: Berlin, Germany

Post by Navs » Sat Sep 14, 2019 3:56 am

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
Ambient Wiggler
Posts: 3823
Joined: Wed Mar 31, 2010 6:01 pm

Post by polyroy » Sun Sep 22, 2019 3:07 pm

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.

Post Reply

Return to “Music Tech DIY”