Hey guys,
I recently built a fuzz pedal using the zombii pcb. The pedal worked for a little bit and then stopped working correctly. When the pedal is on the output is real quite and not fuzzy at all.
I checked the transistors they seem to be alright. However the voltage drops across the germanium transistors were .136 volts and I read somewhere that the drops across the transistors should be .45-.9 volts. I'm not sure if that specification includes germanium transistors though.
The only other problem I encountered was when I checked the capacitance of C2. When the capacitor was soldered to the board the reading was not 100nF it was something really small. When I took C2 off the pcb and checked the capacitance it was right around 100nF.
Any ideas? Any help is greatly appreciated.
Thanks
That's interesting. Sorry to hear you're having a problem, and welcome to the forum! Hopefully we'll get you working right.
My experience has been that if something was working and now isn't, either something has failed, something has come loose, or the wrong kind of power has been applied.
The last is easiest to check - what's you voltage at your source, and what's your voltage at the 9V in on the board?
The next is also easier - check all the wiring to make sure you properly soldered everything by using a DMM to check the connectivity so you know no wires have either been improperly soldered or have come loose.
The first is the hardest. Caps and resistors are very unlikely, and since all that's left in your circuit is Transistors and Diodes, those are what you have to check. If you can replace them, that can be definitive, and if it doesn't work then it's not that. If it is, then you've solved the problem. The main reason for part failure is either poor manufacture, or improper power application. You can't prevent the first, but double check you're using the right kind of power supply for you parts.
So if all of that checks out, I recommend building an audio probe to help you nail down where the problem lies in the circuit if you can.
Jacob
Thanks for the help Jacob. I just read your thread and watched your video on how to use and build the audio probe. I'm gonna have to build one. Seems like a pretty useful tool.
I'm just using a one spot 9v supply I'm getting a reading of 9.4 volts at the 9v node and at the source. So I don't think that's the problem. Hopefully I'll be able to narrow it down after I build the audio probe.
What is your voltage at lug 3 of the stab pot with it turned fully clockwise?
The voltage at lug 3 of the stab is reading 1.3mV
You should be close to 9v at lug 3 of the stab with it fully clockwise.
How do you have the pots wired? Could they be backwards?
I suppose they could be backwards but I checked the wiring several times. The pot lugs are wired from left to right 1 2 3 when looking at one straight on correct? Like the picture in this thread...
http://www.diystompboxes.com/smfforum/index.php?topic=84035.0 (http://www.diystompboxes.com/smfforum/index.php?topic=84035.0)
Yeah, if your looking at them from the front, it's 1,2,3 from left to right... and vice versa (3,2,1, left to right) if your looking at the pot from the back...
Also, I know it's kind of obvious but, make sure you have your pinouts for your transistors correct (red dot usually marks collector on germaniums, I believe... but not all the time). A tell-tale sign of this, I found, is if the circuit pops really loud when you turn it on, the pinout is probably wrong.
Of course the transistors could have been over-heated for the germanium ones if they weren't socketed... IDK, probably not likely though, just throwing it out there.
Another idea that I use to spot solder bridges is, to get a printout of the pcb image and hold it in front of a lamp so you can see the traces through the paper, as it would appear on the actual board... this way you can spot any solder bridges (things connecting that aren't supposed too) on the board, without being confused by a reversed pcb image.
IDK, just some ideas I thought might be helpful.
Oh yeah, and if you can (after your positive it's not something on the actual circuit board thats wrong), check that your pots are getting the right resistance reading... pull one leg off and measure w/ your dmm, putting one dmm lead on the leg you pulled out of the circuit, and the other lead to the middle (wiper) lug. It should read almost (w/ the 20% tolerance in mind) the resistance of the actual pot value.... I just had a problem w/ this, on a recent build that, worked a day or two, and just randomly decided not to work.... right GTR2? ;)
Thanks for all the tips guys.
First off sorry I've been taking so long to respond to any of these. I've been busy as hell lately. Anyways I checked the pot resistances and that turned out pretty interesting. One of the 10k pots is only reading 5k and one of the 5k pots will sometimes steadily read around 300k but also sometimes read 7M and start decreasing slowly. I think I have an extra 5k and 10k pot laying around I'll look into replacing those.
hmm... two bad pots seem pretty unlikely
how are you measuring them? Your readings seem unusual even if they were bad.
For the stab pot you should pull the wire off of lug 2 and measure the resistance between lugs 2 and 3
At fully clockwise you should have close to 0 ohms at full counterclockwise you should have around 5k.
Pictures would also help us see how you have things wired.
Josh