Debug: Maxon OD-808 vero

[sco01]

Hi guys,

I would appreciate your help with debugging a Maxon OD-808 vero project.
This is my fifth scratch build and I have been debugging it the last couple of nights with no results and I'm now humbly asking for your input.

Problem Description:
I get clean signal thru when the balance pot is turned to max. No signal when balance is turned to bottom.
The OD pot has no effect at all (except for a tiny bit of scratch noice when turned).
The Tone pot does affect the tone of the clean signal.

Details:
Based on the Maxon OD-808, Rev1 vero Layout by Harald Sabro Bolstad at sabrotone.com
http://www.sabrotone.com/wp-content/uploads/2011/08/MaxonOD-808.gif
Vero in turn based on the Maxon OD-808 Ver 1.2 Schematic by Matsumin dated 2005-12-24
http://www.matsumin.net/diy/bunkai/od-808/OD-808_sch.BMP
Modifications: None
Substitutions: R11: 56K instead of 51K, C1 47pF instead of 50pF
Battery Voltage: 8.92V

Readouts (Component IDs from vero layout)

D1: A:4.41V, C:4.56V
D2: A:4.56V, C:4.41V
D3: A:0V, C: 8.82V

IC1:
1. 4.38V
2. 4.39V
3. 2.92V
4. 0V
5. 4.35V
6. 4.59V
7. 4.44V
8. 8.88V

IC2:
1. 4.45V
2. 4.44V
3. 4.44V
4. 0V
5. 4.01V
6. 4.43V
7. 4.43V
8. 8.87V

Images are available here: http://imgur.com/a/N2TYn



//Stefan

[R O Tiree]

Hi Stefan,

First off the schematic was done by someone from Japan (?) so you can see how the concept of "level" might get translated into "balance". It's a volume control.

Second, I think you have a 47pF cap in the C2 spot (e13 to h13).  This should be a 47nF cap.

Third, just to be sure, I'd take an old craft knife and run it down the gaps between all the traces and get rid of any half-burnt flux in there - burnt flux leaves a carbonaceous residue, and can provide a resistive path from trace to trace - not what you want in a high-gain pedal.  It's also possible that you've got a couple of whiskers of copper hanging about from where you did your cuts (I can see that you've cleaned some of them up) and, if they join up with a microscopic whisker of solder, you can get a short circuit. Vero's a pain for this and running down the grooves with that craft knife will also break those shorts (if there are any).

Lastly, I'd check that no flux from the solder has dribbled into the Overdrive pot carbon track.

Hope you get it running

[sco01]

Thanks!

That 47nF cap did the trick. Silly mistake. This is a pretty sweet-sounding pedal now. Thanks for the tip on the flux on the carbon track of the pot too. I can see how that can happen and that can explain a few scratchy pots on some previous builds. I will mask the holes on the pots before soldering from now on.

//Stefan

[R O Tiree]

Glad to have helped