SOLVED Abyss rate led stuck on

[cniers13]

Hello everyone,

Just finished wiring up my abyss pedal. Sounded great and then I noticed the rate led stopped pulsing and is now stuck always lit up. I reflowed as many solder joints as I could and cleaned the board up too. Any ideas?

 

[cniers13]

So on the schematic, I traced out everything connected to q1, aka that whole bottom section. Everything looked good and continuity was where it should be

 

[cniers13]

Looks like q1c voltage did not change when the speed pot was adjusted. Still around that 2.13 V range

 

[cniers13]

Going to redo the rate pot today and clean up any solder under that pot. Hopefully that solves it. If not I'll try the new caps next!

 

[cniers13]

Updated, swapped out C11-c13 with tant caps, and resoldered the rate pot. LED would pulse for about 2 seconds and then it stayed lit the whole time. Everything looks clean and no debris/cold joints to my knowledge

 

[cniers13]

@Chuck D. Bones or @zgrav any ideas? I can send more pictures if you need

 

[Chuck D. Bones]

The LFO is on the edge of working. The power up transient kick-starts the LFO, but it doesn't have enough gain to sustain oscillations. A common problem with phase-shift sinewave oscillators.

I see you used a solder-lug pot for RATE. Are you sure it's B100K? If the two gangs don't track well, that could also stop the oscillator. It can be checked in-circuit. With the power off, set RATE to 0. Measure resistance from ground to pin 3 on one gang and then the other. You have to wait for the reading on the meter to stabilize. Verify that the resistance values match within 10%. Then set RATE to noon and repeat.

Try removing all of the electrical tape on the RATE pot. It might be introducing a leakage path.

 

[cniers13]

The LFO is on the edge of working. The power up transient kick-starts the LFO, but it doesn't have enough gain to sustain oscillations. A common problem with phase-shift sinewave oscillators.

I see you used a solder-lug pot for RATE. Are you sure it's B100K? If the two gangs don't track well, that could also stop the oscillator. It can be checked in-circuit. With the power off, set RATE to 0. Measure resistance from ground to pin 3 on one gang and then the other. You have to wait for the reading on the meter to stabilize. Verify that the resistance values match within 10%. Then set RATE to noon and repeat.

Try removing all of the electrical tape on the RATE pot. It might be introducing a leakage path.

So they are not close at all. Top was at 219k and bottom was 67k

 

[cniers13]

I think I might have a cold joint as well. When I try to measure resistance on the lug it works but when I measure it on the pad it isn't reading out or it bounces around

 

[Chuck D. Bones]

Either the pot has a problem or R17 or R18 are the wrong value. Swap the polarity on the meter leads to ensure that C11-C13 are not interfering with the measurement. At the low voltage applied by any decent DMM when measuring resistance, capacitor polarity should not be an issue.

 

[cniers13]

r17 and r18 are both 220k so that's good. Remeasured and got the same values as previous post, with the bottom gang around 68k

 

[cniers13]

did a reflow and now they are both around 50k

 

[cniers13]

update, plugged it in and the rate was working for longer but I moved the PCB and it was intermittent when I moved the PCB around

 

[cniers13]

well c9 is 100uf and i have 10uf, swapped that and no changes. it worked for a little bit and then stopped again

 

[cniers13]

FINALLY, so I grabbed a new rate pot and soldered it with wire, it's long but it works. Redid all the solder joints I can get to and it seems like it is finally working. Thank you for all the help. If I report any issues I will come back but hopefully, this thread is closed! Onto the next builds!!!!

 

[Chuck D. Bones]

That's great! Mark it SOLVED.