Boss SD-1 passes very weak signal when active

[kvandekrol]

OK... I just did the SD-808 mod to my SD-1 because I was borrowing a Tubescreamer and wanted to see how close it sounded. I'm pretty comfortable with soldering and have modded about 5 pedals in the past, all successfully.

Here's the mod I did:



But I went to test it out, and found that when I engaged the pedal I could barely hear it. It's like the volume was reduced by about 95%, even with the Level set to full. The Level, Drive and Tone knobs still have an effect on the tone, it's just barely audible. When the pedal is turned off, it passes the signal just fine.

Since it was such an easy mod and I've done this before, I didn't test after every component swap. But what I did do was return the pedal to stock one piece at a time, testing after every reversion. I ended up all my changes reverted, the pedal back to stock, and still it has almost no volume. It's a newer SD-1 as well - I bought it used, but it was only a couple of years old tops and it was basically mint when I got it.

I don't know where else to look. I've triple-checked everything. I was very quick and attentive in my soldering (you've heard this a million times) and I really don't think I overheated anything or installed it wrong. I tested the continuity on every component I touched and it all tested fine.

Any ideas what could cause this problem so I know where to focus my efforts? If the tone is affected by the knobs then I would assume the volume is being constricted at some point later in the circuit, like C10, R16 or R17 where I made the mods... but again... switching these back to stock has had no effect!

Thanks for your help...

[kvandekrol]

Updates:

Link to the schematic

At suggestion from the debugging sticky post, here are the voltages on each of the transistors and diodes as well as the IC:

Q1 - K30A
1 - Source - 4.54
2 - Gate - 1.31
3 - Drain - 3.19

Q2 - K30A
1 - S - 4.12
2 - G - -0.01 (negative)
3 - D - 3.14

Q3 - C2458
1 - E - 0
2 - C - .05
3 - B - 0.63

Q4 - C2458
1 - E - 0
2 - C - 5.99
3 - B - 0.02

Q5 - C2240
1 - E - 3.48
2 - C - 9.19
3 - B - 3.88

Q6 - C2240
1 - E - 2.99
2 - C - 9.19
3 - B - 3.29

IC - JRC4558DD
1 - 4.51
2 - 4.51
3 - 4.50
4 - 0
5 - 4.46
6 - 4.51
7 - 4.51
8 - 9.17

D1
A - 0
C - 9.13

D2
A - 4.45
C - 9.13

D3 - jumper - 0

D4
A - 4.5
C - 4.49

D5
A - 4.36
C - 4.49

D6
A - 4.49
C - 4.36

D7
A - 1.15
C - 2.99

D8
A - -0.13 (negative)
C - 0.05

[zombiwoof]

I don't know how long you've had the SD-1, but just thought I'd ask:  How are you powering the pedal?.  Is it an older one that requires an ACA adapter?.  Maybe you already know this, but the older ones used an unregulated adaptor, and have a couple of components that brought down the 13+ volts that the ACA adapter put out.  If you are trying to power it with a regulated 9 volt adapter, it won't work right.

My apologies if this doesn't pertain to your SD-1, but it was worth a shot.

Al

[kvandekrol]

I've had it for about 3 months but I don't think it's more than 5 years old. I did try both a wall wart and a new 9v battery but same story both ways...

[kvandekrol]

So, turns out flux can be conductive... I was poking around with an audio probe when I accidentally bumped a non-trace (dark green) part of the PCB and to my surprise heard a signal. So I dragged it around the board and the sound came and went. I found that any time I touched leftover flux residue, I heard sound... After cleaning the circuit board thoroughly, everything worked fine. So I re-did the mod and it sounds fantastic.

This also comes after I just got a new kind of flux from Home Depot, a brand I'd never used before. Explains why I've never had the problem before now. I would have cleaned up the flux before I put the pedal back together, but the problem kept me from putting it back together until I figured out what it was.

Sounds like I'll be getting a new kind of flux, and strangling the man who invented this concoction. It's Home Depot water-soluble flux, BTW. The water-soluble stuff from Radio Shack doesn't have this problem.

[TheFantod]

please ignore! Sorry!