Control PCB problems

hey everyone

I had to do some repair on my faceplate last wkend (Gorilla “fast dry” glue, not as strong as the regular stuff, and once that was done I was ready to let loose - but wait) things aren’t working properly! Here’s the report:

•knob1 is only outputting to “82,” knobs 2-4 outputting to “41”
•knobs 1 + 2 are “twitchy” jumping back/forth between close values
•these are regardless of which section I am in (buttons working fine).

my lil diagnosis: SOMETHING is WRONG. to the naked eye everything seems fine…I even re-soldered the GND connection on the rainbow cable bc it looked funky. no change.

any hints?

There’s something wrong in the path of the >ANL line. At best it’s a wrong joint/damaged cable - you can also check that there is no short with the neighbouring lines. In very, very last resort, the 4051 multiplexing the pots signal is not good.

I’m not finding a short on the rainbow connector. I resoldering some connections that were looking rough just to be sure, but the problem remains. How would I verify that the 4051 has crapped out?

frustrated b/c everything was 110% awesome. ack.

Put a voltmeter on >ANL. You should read here a voltage which is the average of the values of the knobs. All knobs fully rotated clockwise: 5V. All knobs fully rotated counterclockwise: 0V. One of them: 1.25V, etc.

The multiplexer responsible for scanning the knobs is IC5.

knob 1 100% clockwise = .8

knob 1 + 2 = 1.6

knob 1 + 2 + 3 = 2.4

all knobs clockwise = 3.2

ok. is there a chance that the power distro is funky? I did need to re-solder the connection for my power switch when assembling the case, but the synth did work fine after that…

sorry this is taking me some time to step through but argh employment.

If you have 5V on the control PCB’s 5V input, it means there’s a voltage drop somewhere. Check the continuity between the 5V pad and the right pin of each pot. If you want me to reorder a control PCB, let me know - I’ll reorder one the next time I do a PCBCart order.

continuity seems to be fine. maybe I’m missing something? I’m getting a little cranky about this.