Debugging a Menatone Red Snapper

[suryabeep]

Hi everyone,
I built a Menatone red snapper from the layout here : https://tagboardeffects.blogspot.com/2012/04/menatone-red-snapper-4-knob.html . As expected, it doesn't work on the first try  . IC voltages are:
pin1 :8.05V
pin2: 4.44V
pin3: 4.04V
pin4: 0V
pin5: 4.45V
pin6: 4.45V
pin7: 4.45V
pin8: 8.94V
The pedal doesn't produce sound when engaged. However when I put my thumb on the bottom of the board to short some pins near the IC the clean sound comes through (no drive, bite/cut don't do anything). As far as I can tell I've followed the layout exactly without any modifications. What could be the problem?

[PRR]

> As expected, it doesn't work

I want to be snide and say that any plan with no schematic is a poor pick.

But that is not always true.

But if/when it does not work, debugging is way too much work to figure out without a *functional* diagram (instead of a *mechanical* diagram).

From some experience, your pins 1,2,3 voltage should be the same, half-supply, and ain't. More thought suggests that pin 3 has a leak to ground and by op-amp action this throws pin 1 against the ceiling. But I don't know what those pins really do and tracing a zig-zag through strip-board is not my idea of a fun Saturday night.

[Mark Hammer]

I have to concur.   As much as I commend the effort and dedication that people put into producing them, personally, I find the tagboard/vero layouts exasperating, in the absence of a schematic.  How does one deduce the source of any  problems if the circuit doesn't fire up flawlessly first time?  If you don't know what is supposed to be connected or isolated from something else - by DESIGN - how can you tell if this lead is misplaced on this line or not?  How do you easily flag a cut you meant to make but didn't?

[reddesert]

The tagboardeffects layouts all have schematics, but the schematics are mostly on the "other forum" [FSB], or very occasionally in the forum hosted at tagboardeffects itself, and are not duplicated on the blog for copyright reasons and the tender sensibilities of a few people.  They can virtually all be found with a search.

To the OP, what you should do is find the schematic, and build an audio probe (instructions at RG Keen's website), figure out how the schematic corresponds to the layout, then probe the layout following the signal path until you find where the audio disappears. This will typically indicate an unsoldered or shorted connection. Strategic voltage readings can help find errors as well (like transistors whose base should be at Vref but is at ground, etc).

Nearly all of my build errors are leads that I forgot to solder and didn't notice; other people may have different errors, depending on their method.

That sounds like a giant handful, but it's not actually that hard. Do it a few times, and you will gain an understanding of how the signal and bias voltages travel through circuits, and really have learned something.

[suryabeep]

Thanks for the suggestions, I will go an make an audio probe asap and see if I can diagnose the fault. I'll report back soon!

[suryabeep]

Alright, I made a super ghetto audio probe, using a looper to feed in guitar signal, all controls are maxed. Here's what I'm getting:
IC pin1:very loud, distortion (good kind)
pin2: not as loud, no distortion.
pin3: same level as pin2, no distortion
pin4,5,6,7,8: nothing

I also traced the signal flow up to the bite control. The Bite is wired weirdly (I think) - there's stuff connected to lugs 2 and 3 but nothing to lug 1. I get audio on lugs 1 and 2 when the knob is all the way CCW.
The signal seems to stop at the 22uf electro cap, there's no signal at either end of it.
There's no audio  at all on the right side of the board.

Guess what?

Nearly all of my build errors are leads that I forgot to solder and didn't notice; other people may have different errors, depending on their method.

There was a cold joint at the jumper near pin 1 of the IC. I reflowed it and it works now!!!
A big Thank You to everyone who helped! I can totally see the benefit of an audio probe now, I'm wondering why I didn't build one before