| Q1 | Q2 | Q3 | |
|---|---|---|---|
| Pin 1 | 1.70 | 4.07 | 4.46 |
| Pin 2 | 1.66 | 1.94 | 4.06 |
| Pin 3 | 0.25 | 0.02 | 1.95 |
The top left pad should be connected to the ground plane. The bottom right should have continuity with upper pad of R2.
That’s only superficial as it was lightly marred during component replacement; the issue was present before the capacitor was swapped and any surface damage done.
My bad, I should have specified that it looks like the solder connection for the ground plane is bad. Probably not the source of the issue, but less power filtering could possibly exacerbate the issue
A reflow appears to generally be in order, true
Q1I'm hoping that getting more eyes on this will help us find the issue. Here's the schematic for reference:
Things we've tried already (in no particular order):
I don't see any obvious solder bridges, so that's good. It's probably still worthwhile to reflow the joints just in case. Also, do you have an audio probe?
- Increase C4. Pitch changes, but still sounds like a foghorn.
- Replace the electrolytics. No change.
- Increase R3 and/or R5 to reduce gain. No oscilation when guitar is disconnected. Oscilation comes back with the guitar is plugged in.
It's probably also worthwhile to check the voltages at the legs of each transistor. Be sure to install stock values for R3 and R5 before checking. Here are the voltages on my working copy:
Q1 Q2 Q3 Pin 1 1.70 4.07 4.46 Pin 2 1.66 1.94 4.06 Pin 3 0.25 0.02 1.95
(I powered the pedal using a One Spot with 9.4V output.)
It operates with no issues apart from the oscillation at the highest ranges of the fuzz, so it doesn’t present like a damaged trace…not that I’m aware of. That and no populating work I did really could’ve damaged a trace.
What does R1 measure at? Do you have a free BS170 you could swap Q1 out for?
Almost 1M exactly. I just ordered a few more from SBP but nothing on hand presently.
