Non-working EHX Big Muff V2

[Gallagher90]

Hi folks!

I got my hand on a 75'ish Big Muff that did not work according to the seller. The seller (or some former owner) had the ON/OFF switch removed for some reason and the pedal also had some plastic non-original tele jack at the Input and still has a stereo Output jack (which is not original?).

I changed the Input jack to a original EHX mono jack from my 78' Dr Q (has one left) and I also took the ON/OFF switch from my Dr Q to put in my ''new'' Big Muff so I easiler could re-solder the cables. I've found like 8-10 pictures of different V2s and all are soldered different in some way so feel free to point out if some cable is in the wrong place.

Note that the ON/OFF switch has 6 soldering point instead of 3 that the Big Muffs usually have so I'm not shure if I got the soldering right there.

The pedal works in bypassed mode and I can hear my guitar clearly but when I turn on the pedal theres no sound or hum or nothing. You can only hear a slight electric flicking sound when turning the ON/OFF switch back and forth.

The battery is charged and the battery cable measures 8,5 v.

I'll ad some photos.



And I'll also add this photo of all the components on the board which is pretty much the same as my pedal so the values of all components/caps should be pretty much the same if not identical.



I also measured all resistors and caps just to make things easier.

Heres the values.

Big muff V2 voltage measuring


Right to left starting from grund field low right (picture 1)

First row

1.   6.22 v - Brown area
2.   1.458 v – Brown area
3.   1.638 v – Brown area
4.   6.8 v – Brown area
5.   0.826 v (small green cap to ground) – No color area
6.   0.215 v – purple area
7.   7.47 v – red area
8.   0.072 v – red area
9.   0.413 v – red area
10.   0.159 v – purple area
11.   7.43 v – orange area
12.   0.095 v – orange area
13.   0.394 v – orange area
14.   7.63 v – blue area
15.   0.09 v – blue area
16.   0.238 v – blue area
17.   0.0 v – green area

Second row

1.   0.807 v, Q1 – brown area
2.   0.969 v, Q2 – red area
3.   0.927 v, Q3 – orange area
4.   0.778 v, Q4 – blue area

Third row, working right to left upp and down (picture 1)

1.   2.250 v – white can cap – purple area
2.   0.0 v – resistance low – red area
3.    0.0 v – resistance middle – red area
4.    0.513 v – orange cap – red area
5.    1.477 v – white box cap – brown area
6.    0.626 v – green cap – red area
7.    0.626 v – resistance (same as green cap next to it. I'd say 0.0 v) – red area
8.    0.0 v– resistance – red area
9.    0.602 v – white box cap – red area
10.    0.880 v – orange cap – purple area
11.    0.009 v – resistance – orange area
12.    0.007 v – resistance – orange area
13.     0.550 v – white can (counting down while measuring?) – orange area
14.    0.395 v – white box cap (looks burned/fried on one corner) – orange arae
15.    0.624 v – green cap – orange area
16.    0.624 v – resistance (same as green cap next to it. I'd say 0.0 v) – orange area
17.    0.0 v – resistance – orange area
18.    0.0v – resistance – blue area
19.    0.629 v – green cap – blue area
20.    0.862 v – white box cap – green area
21.    0.195 v – white can cap – blue area
22.     0.629 v – resistance (same as green cap next to it. I'd say 0.0 v) – blue area

I'll appreciate all help I can get.
/C.

[thermionix]

The On-Off switch is probably okay how you have it.  Somebody took it out and then added the stereo jack to turn the battery off when the cable was unplugged.

Can you give us just the voltages for just the 4 transistors?  Do you know what an audio probe is?  Very easy to hack one together with a cap and some wire, you can do a search here.  But first, transistor voltages.

[Gallagher90]

The transistors are the 3-legged guys right? G1-G4? I've written the voltage for them already in the voltage list. ''Second row''. It's DCv right and not ACv?

1.   0.807 v, Q1 – brown area
2.   0.969 v, Q2 – red area
3.   0.927 v, Q3 – orange area
4.   0.778 v, Q4 – blue area

I googled ''audio probe''. Can you buy them or do you need to make them? I'm not that good with electrical technical stuff. I've only been working with guitars which I find much easier. Been soldering quite a bit.

[thermionix]

Q1-Q4, yeah.  We would be most interested in the collector voltages, but you can give all 3 voltages for each transistor if you don't know which leg is the collector.  DC volts, yes.

Audio probe.  Imagine a standard guitar cable, but you cut one plug off.  On the newly free end, strip back several inches, and solder the shield to an alligator clip.  Solder the "hot" to one leg of a capacitor, say .047µF or something close to that.  You can use a guitar tone cap.  It needs to have a voltage rating higher than the voltages present in whatever you're probing, but that's almost any cap for a 9v pedal.  The free leg of the cap is now your "probe" and you connect the alligator cap to ground (enclosure) of the device you're probing.  Plug the other end of the cable into an amp, put some kind of signal into the pedal you're probing.  If you follow the signal through the circuit, you can find where it stops.  The cap blocks DC, but allows signal through to the test amp.  Hope that makes sense.  I know I said "a cap and some wire" above, but best would be a cheap instrument cable, a cap, and an alligator clip.  And some heat shrink tubing to hold it all together.

[Gallagher90]

Ok here's all 4 volt values for the transistors. (looking at the 1st picture I measured as followed. 1st: bottom and left soldering point, 2nd left and top, 3rd: bottom and top.

Q1: 1st- 0.193v, 2nd- 0.618v, 3rd-0.814v
Q2: 1st-0.339v, 2nd-0.627v, 3rd-0.970v
Q3: 1st-0.300v, 2nd-0.626v 3rd- 0.979v
Q4: 1st-0.148v, 2nd-0.629v, 3rd- 0.778v

So I can make a audio probe just by cutting a old jack cable, scale the cable and use a higher cap (think i have one .047uF lying around) solder that to the hot cable. Couldn't you just scale the ground cable of the audio probe and pinch it on the pedal casing so it stays grounded? as long as it's firm agains metal and don't fall of?

Yep found some new unused caps. two tropical fish and one which i think is a 0.047uF (says 473 on it).

[Gallagher90]

So the audio probe is finished.



Am I supposed the hear a hum or something of the signal in the pedal all the way trough the board until I find a faulty cap, transistor or resistance which is dead quiet while putting my guitar in Input and the probe in an amp? or does a faulty component make a strange noise different from working ones?

[Gallagher90]

So I tried the audio probe out. Don't really know what to listen for and if I did it right but when I touched all soldering spots the amp gave out a quite loud ''poff'' sound on all components except one that only made the same sound if touching another component just before. otherwise it was not giving any sound.

The component I'm referring to is the resistance in the blue area (picture 2) just next to one of the white box caps. nr 18 third row in my voltage list. Should be a 39K resistance according to the picture.

The resistance looks flawless.

[Kevin Mitchell]

At the risk of replying without reading through everything here...

You need to follow the guitar signal with the probe to see where it's disappearing. Wherever that spot is would give an idea of where an issue could be. Like if you probe the center lug of the tone pot and the signal is there but not at the output, you'd know the problem is either the last transistor, one of it's connections or the effect board's output wiring.

I think this is the schematic

[Gallagher90]

Well that makes sense of course. Only dilemma is that I do not understand wiring diagrams/schematics at all.

But as I understand (if i understand correctly) the board is splitted in 4 sections (se picture 2). 1 input/sustain, 1 tone, 1 something else and 1 volume/output? So if that's the case should not the signal go from first section to second and working it's way on in that manner?

[Gallagher90]

Picture 2 again.

[Kevin Mitchell]

Schematics are super simple to follow. For this circuit the signal passes through the 3rd pin (the collector) of each of the 4 transistors. So probe those and see where the signal is disappearing.

Let us know what you find.

[Kevin Mitchell]

Yes the signal for this pedal is passing through each section one at a time. The schematic I've linked actually color codes to accommodate the sections in the photo you keep referring to.

[Gallagher90]

Now I've got it.

The signal went trough the first transistor. I could hear the signal trough all of the first ''sections'' as I described in the post prior to this. I do not get any signal from the top white box cap but from the resistance next to it. The one box cap I mentioned looked ''fried'' (nr 14 third row that has lower volt then the rest of the box caps).

EDIT: Is the white box cap I mention the ''C4'' in the schematic you linked to?

[Gallagher90]

Also checked the Sustain pot. There's only the left pin that gives out sound and no sound from the middle pin and the right. Faulty/dirty pot perhaps?

[Kevin Mitchell]

Also checked the Sustain pot. There's only the left pin that gives out sound and no sound from the middle pin and the right. Faulty/dirty pot perhaps?

This would give me the impression that the control is turned fully counter clockwise. That would be like having your guitar volume all the way down and asking why you can't hear anything. The signal would not be at the 1st pin but when fully clockwise it should be at both pin 2 and 3 - it'll always be on pin 3.

About C4, if you have signal at pin 3 of the sustain control then whatever cap you're talking about is not C4.

Post a photo of your unit and explain to the best of your knowledge.

EDIT - you said left pin. Those pots are upside down and sideways on the board so I'm guessing we would reference the lugs different from your perspective. Just a thought.

[Gallagher90]

Worked the Sustain pot back and forth 30 times and now the middle pin/leg also sends the signal so now I get the signal on the first 3 transistors.

Think all 3 pots needs some cleaning after all this time and perhaps that will fix the entire issue.

[Kevin Mitchell]

That's great. Of course you should see what's going on with the tone control if that's where the signal dies before getting to the 4th transistor. FOLLOW THAT SIGNAL

[Gallagher90]

Turned the Sustain all the way up but still only the left and middle gives out signal.

I've might been mistaken about the C4. The white box cap is supposed to be 0.01uF. Anyway that cap gives signal now as well since the sustain pots middle leg goes straight to that cap and it sends the signal on so no fault there.

[Kevin Mitchell]

The way potentiometers work and how that's wired the signal would not be at that lug in any setting. So you can move on. With the control all the way up that means there is 0 resistance between lug 3 (pot input) and lug 2 (pot output) so the signal is at it's fullest.

Your "left" pin is traditionally the right pin. The pot's just upside down (worth noting again)

[Gallagher90]

Now I seem to get a signal all over the board except for the ground part. Are you supposed to hear the signal in the ground part of the board?

Edit: Noticed your noting on the pots. Yes of course they are upside down I'm of course referring to them in the perspective I work which is open pedal turned upside down.