Where to start troubleshooting a fuzz?

[aBunchOfPedals]

Hello,

I finished my second DIY pedal (http://www.rullywow.com/product/king-tut-fuzz-pharoh-clone-pcb/) and I obviously screwed up somewhere.  I was all excited to try it out and it didn't work.... kinda.  The true bypass works, so there's that.  It's SUPER quiet and the led doesn't turn off.  How do I even begin to troubleshoot this?  I took some pictures if it helps.

http://imgur.com/a/SsMCR

My first was a simple compressor and it works great (for the last 4 years and it's still on my board).

[natron_mn]

Your diode and transistor orientation seems correct, and it looks like you are wired from the footswitch to the jacks, dc and main pcb correctly. I can't read the transistors to see if you put the MPSA18 where a 2N5088 should have gone, but I'm guessing those are all correct.

So I guess my next thought would be to measure the voltages at the transistors and some other folks here who know more about appropriate readings can go from there!

A side note - I think I've had trouble with glass diodes before. If there is a crack in them then they won't work. I try to socket those. I also socket the transistors, since those can get fried pretty quickly from a soldering iron. I don't think the 2N5088s are as sensitive as other transistors, but not sure about the MPSA18. Either way, it's always helpful to socket transistors in case you want to experiment or swap out a bad one.

[GibsonGM]

I'd try to audio probe the signal path - see if the signal makes it TO the base of the 1st transistor. Then you know the switch IS passing the signal in...
You'll use an audio probe in the future, too, so make one now    

If you put the MPSA18 in where the 5088 goes, it would work, just not properly.  Find the transistor collectors, and listen for signal at them - at the input, and output.

The trannies aren't THAT sensitive - just solder them quickly (like, a "3 count", then pause before doing the next leg).

Audio probe:
http://www.diystompboxes.com/pedals/debug.html

[R.G.]

How do I even begin to troubleshoot this?  I took some pictures if it helps.

Welcome. One very good beginning would be to notice that at the head of all the posts here in the forum, there is a stickie topic entitled "Debugging thread: what to do when it doesn't work".

My best suggestion is to go and read that thread. It was written if not for you, for your predicament.

[natron_mn]

Thanks Gibson. I'm still learning but I thought I'd try to put what I've learned to try and help. But your tips will help me with my own troubleshooting! Sound advice.

[aBunchOfPedals]

Thanks for the advice, I'll go through the trouble shooting page and get an audio probe.

[GibsonGM]

Thanks for the advice, I'll go through the trouble shooting page and get an audio probe.

Well, you make it....if you have an extra capacitor around, the rest is easily-found junkbox stuff.  Remember, if you want to use this probe on higher voltage things, you need to make sure that cap is rated for a voltage higher than what you work on.  But for what we do, 9V, a 16v or higher cap is fine. 


Natron - there's no point where it's too soon to try to help someone    You saw a different part # there and keyed in on it, that is very good!