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Help with plague bearer build please!
MUFF WIGGLER Forum Index -> Flight of Harmony  
Author Help with plague bearer build please!
Bonobo
help

Just finished the plague bearer which is my first SMC build, connected it all up and got a bit of a burning smell and some other modules in the rack went a bit nuts.

Plugged it into a little empty case and it seems to be working, however the 'high' and 'gain' knobs don't seem to work correctly. 'High' does nothing and gain does almost nothing, when I connect the CV inputs for those functions and use a +10v offset from frames they work clearly as I'd expect.

The variable resister for 'high' looks to have burned and has a black burn mark on it, nothing visible on the gain one.

So.. any suggestions on what to check before I replace the high VR since I don't want to just burn through another one.

Any help appreciated!
Bonobo
Any pointers on where to source a replacement potentiometer would be helpful as well, mouser don't seem to do one that'll work, only a horizontal version very frustrating
flight
Bonobo wrote:
help

Just finished the plague bearer which is my first SMC build, connected it all up and got a bit of a burning smell and some other modules in the rack went a bit nuts.

Plugged it into a little empty case and it seems to be working, however the 'high' and 'gain' knobs don't seem to work correctly. 'High' does nothing and gain does almost nothing, when I connect the CV inputs for those functions and use a +10v offset from frames they work clearly as I'd expect.

The variable resister for 'high' looks to have burned and has a black burn mark on it, nothing visible on the gain one.

So.. any suggestions on what to check before I replace the high VR since I don't want to just burn through another one.

Any help appreciated!
Happy to help! Please post some high-resolution pictures of the front & back of your PCB and we can go from there.

Bonobo wrote:
Any pointers on where to source a replacement potentiometer would be helpful as well, mouser don't seem to do one that'll work, only a horizontal version very frustrating
I happen to have a few of those on hand and will send you one for $1.00 + shipping (PM me with your address), but lets figure the issue out before you swap it in.
Bonobo
Thanks so much for the help SlayerBadger!

My first effort at surface mount soldering so its not pretty hihi
[url]
https://imgur.com/a/BwSu9dg#GX7FMx7
[/url]
Cap on the back got melted somehow, I was planning to replace this just in case it was the cause and they have them in mouser.

You can see the burn mark on the high pot in the last pic.
flight
Don't worry about the cap, I've melted a few and they work fine as long as you haven't melted through the yellow plastic casing.

I can't see what might have caused the problem yet, but it does look like Q1 popped as well.

Could you take some more pictures that show angle or side views of the components (like in the one that shows the burn on the high pot) please? It looks like there might be a few cold solder joints.
Bonobo
Good news about the cap, its surprisingly hard to get the photos to focus so I took a good few.

https://imgur.com/a/JYpEX76
flight
eek! Um, I think I found the problem.

There's a potentiometer nut under the high pot. It looks like it probably shorted the wiper to ground - which is why it affected your other modules - and is offsetting the CV input. I'm not sure about the gain pot yet, I'll puzzle on that a bit more, but try taking the nut out and see if that fixes it.
Bonobo
flight wrote:
eek! Um, I think I found the problem.

There's a potentiometer nut under the high pot. It looks like it probably shorted the wiper to ground - which is why it affected your other modules - and is offsetting the CV input. I'm not sure about the gain pot yet, I'll puzzle on that a bit more, but try taking the nut out and see if that fixes it.


lol ohh man, I did wonder why I was missing one. No idea how the hell that happened; thanks!
Bonobo
Found some pots, https://www.thonk.co.uk/shop/alpha-9mm-pots-dshaft/


Is the one I want the 'A100K - D shaft - Alpha Vertical 9mm Potentiometer'
flight
Bonobo wrote:
Found some pots, https://www.thonk.co.uk/shop/alpha-9mm-pots-dshaft/


Is the one I want the 'A100K - D shaft - Alpha Vertical 9mm Potentiometer'
That is the correct one.

If it is damaged, Q1 is an MMBT3904.
Bonobo
Pot replaced and it seems to be sorted nanners It's peanut butter jelly time!

Gain knob still doesn't give me as much range as the CV gain (CV gain will turn a signal to 0 in some cases whereas the knob won't go close) but it does have an effect on the sound thats noticeable. The high is working perfectly and totally killer.

Thanks so much for the help thumbs up
flight
Glad it's working!

The Gain knob isn't supposed to go all the way down to zero output - it's biased to prevent that - so it sounds like it's working right. Enjoy!
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