It's probably not a good thing when....

[Jhouse]

So I was playing through my Big Muff Pi that I recently built using the specs from tonepad.com. I'm sure some of you have seen my various posts about it not working >.<, but I finally got it all fired up and working nice today! Anywho, cutting to the chase, I was playing on it with the knobs wide open and in the middle of me rocking out, the pedal just stopped working. It still bypasses fine, but it just doesn't work when the pedal is on. The only way I can get the pedal to work is if I back off the knob on my POWER SAG that I added in all the way and then I only get my regular guitar signal. Umm, nothing looks fried on the circuit and I don't smell anything burnt. Any ideas on the matter?

Update: When the effect is on and I have my amp cranking I can also get just my guitar signal out of it. It's really soft though.

[MetalUpYerEye]

Dead battery?

It helps to do as the Debugging FAQ says and post all voltages for all pins of transistors, IC's, etc. as well as posting what circuit you used, what modifications and part substitutions have been made and literature for everything (schematics, layouts, etc.)

Otherwise it just makes it really tough for us to diagnose the problem. Imagine that you're a mechanic and someone 3 states away sends you an email that says "my car was working and now it doesn't work, but everything looks OK." How much would you be able to help this person?

[Jhouse]

It's hooked up to a wall wart.

Haha. Good point. I  just thought there was a quick, "Hey, you friend your transistors doofus" fix to the problem seeing it was working just fine. I'll post the voltages on everything here in a moment. Where did I put my meter?

Update: My meter is broken. Great. I'll have to post the voltages in the morning when I grab a new one.

THIS is the layout I used for my pedal. I went with the Green Big Muff Layout.
THE SCHEMATIC is found here.

Mods:

I replaced C5 and C8 with .033 uf capacitors because that was the closest thing I had to .047 uf.
I also took out D1 and put in a spdt toggle switch that gives me the option to switch between D1 as in normally is in its correct orientation, or a series of 6 1n914s in series kind of like THIS.

[Jhouse]

Alright. Got me a new meter. It's analog, but it does its job. These are the values I got for my transistors. Popped a battery into it too, no more using wall warts to test for me. Anyway, the entire board seems to be getting power, but I know something is up with these transistors.

Q1
C= 4.12
B= 0.58
E= 0.19

Q2
C= 0.79
B= 0.50
E= 0.00

Q3
C= 4.61
B= 0.79
E= 0.19

Q4
C= 7.14
B= 0.61
E= 0.98

[Govmnt_Lacky]

Shouldn't Q2 have roughly the same Collector voltage as Q3 

I am no pro.... but that looks like a place to start to me. 

Good Luck 

[Jhouse]

I think it should. Q2 and Q3 are the stages where the distortion is added so I'm not quite sure why they are so different. I think Q2 might be fried or something. :/.
I also don't think there is any reason for Q4 to be as high as it is. I'm not really sure what to do though since the pedal did just stop working all of a sudden.  These are the times that vex men's souls.

[Govmnt_Lacky]

Did you socket the transistors? Do you have spares?

If you said Yes to both... first I would quintuple check your component values, placement, and check for solder bridges and such.

Then you could swap Q2 and Q3 and recheck collector voltages. If the problem swaps.... you have a bad transistor. If not, you have something else wrong in the circuit around Q2.

If you said No to one or both of the questions.... you should order some new transistors... resolder some sockets in ALL the transistor positions... and just replace them all.

BTW.... Did you use the recommended transistors or another alternative?

Good Luck 

[Jhouse]

No I don't spares but I did use 2n5088s. >.<. I used all of them up on this project. Dang it! I need to get some sockets anyway.

[Jhouse]

Well, I switched around Q2 and Q3 and got some interesting results.

Q1
C= 3.98
B= 0.58
E= 0.19

Q2
C= 3.45
B= 0.53
E= 0.06

Q3
C= 3.45
B= 0.45
E= 0.05

Q4
C= 4.00
B= 0.42
E= 0.48

I managed to get the pedal to work!!!!!!.....but only with a battery. Hmmm. I'm going to switch out my dc jack and see if that is what is broken. The pedal cuts in and out sometimes if I jiggle the DC jack even with a battery in.

[Govmnt_Lacky]

Looks like you are getting somewhere fast... 

Don't forget to post your COMPLETE results after you look at the DC jack.

Good Luck 

[Jhouse]

Okay, I'm starting to get flustered. It is not the DC jack as much as I wished that It was. :/. I'm having problems with the voltage sag mod that I added. Basically, I'm running the V+ line from the circuit board to a 10k linear pot wired as a variable resistor. The V+ goes to lugs 2 and 3 and then a wire goes from the first lug of the pot to my DC jack HERE is the site where I got the idea from. It works every now and again, but when I jiggle the wire, the pedal starts to crackle really, really loud. Sometimes the pedal just crackles on its own though. It will change if I move around the wire which I don't really understand because I'm resoldered the silly thing like 20 times.

[phector2004]

Are you using solid-core? Maybe there's a break in the wire connecting your DC jack to the sag pot?

[Jhouse]

I'm using 60/40 rosin core. I just replaced the wire, same problem Hmmm. Could it be the pot?

[phector2004]

I meant for the wire, but if replacing it didn't help... 

[Jhouse]

Haha. Yeah, it's solid core wire too. I'm really befuddled.

[Govmnt_Lacky]

The V+ goes to lugs 2 and 3 and then a wire goes from the first lug of the pot to my DC jack HERE is the site where I got the idea from.

Dude... according to your reference..... you have the pot wired wrong!

You should have your board V+ input wired to lugs 1 & 2. Then, you should have your DC jack wired to Lug 3.

[Jhouse]

Whoops. I always get my lugs mixed up when I start talking about them. Err. Anyway, I have it wired exactly like the diagram has it. I wonder if just taking the pot out of the circuit would fix this issue.

[Govmnt_Lacky]

I wonder if just taking the pot out of the circuit would fix this issue.

Only one way to find out! 

[Jhouse]

Well, that didn't work either. The crackling still happens, so I guess it isn't the pot.

[Govmnt_Lacky]

You need to verify ALL of your off-board wiring. Sounds like you either have a bad/looped ground OR you have an intermittent short of V+ to ground.