Troubleshooting PT2399 Circuits and a Busted Pot

[orangecountylumbertruck]

Hey Guys,

I've been playing around with building several circuits based on a PT2399 delay, which I purchased 2 from pedal parts plus.  The 2 schematics I have been working off of have been the Echo Bender 2, and the Mad beans Cave Dweller.  I've had spotty results with both circuits and chalked that mostly up to my breadboarding skills, until now. 

In building the Cave Dweller, I found that I would get the motor-boating "beep...beep...beep" from the delay pot, and no real audio output.  Other times I would get clean audio from the guitar, but no delay / echo what-so-ever.  After searching forums, I tried swapping out my pt2399s, my LM7805, and using a one-spot 9v PS instead of a battery.  The voltages on my IC look to be inline with what I have seen other people troubleshoot a rebote delay 2.5, seeing close to 5v on pin 1 of the pt2399, and expected voltage on pins 14,15,16.

So long story short, I breadboarded the delay schematic that is on the PT2399 datasheet, went to rat shack and bought a new 50K audio pot, and low and behold, delay.  I then took the 50K pots (non-audio?) I was using on the cave dweller circuit, and noticed that when I used one as the delay pot on the datasheet circuit, that there was no delay, just clean audio, like input going directly to output.  The 2 other pots seemed to test out fine in the datasheet circuit.

Using a multimeter on the suspect 50K pot, I see a full 0->50K ohm R on ground to the wiper and 3rd pin, so it seems like it's not fried....as far as I can tell.  Full disclosure I did have another circuit that this pot might have been on where I released the magic smoke of a 1M pot, so maybe this guy got damaged?  My next plan of action is to try all my 50Ks on the datasheet circuit, and then rebuild the cave dweller with known working pots.

Does any of this make sense, or is there something else I can do to troubleshoot?

Thanks!

[~arph]

The pot can be damaged on the 1st lug too. Does the delay work with the 'broken' pot using only the 2nd and 3rd lug?
Its either that or there is something wrong with the wires to the pot. You have already established that the circuit works with other pots.

[duck_arse]

harsh-ish treatment of pot lugs can make the lugs wiggle a bit, and release the tension of the rivet holding the lug against the carbon track. when this happens, the pot will work sometime, not others, depending on how much movement of the loose lug there is. and the smoke can come out either end of the carbon track, so wired one way it might work, but not the other.

[orangecountylumbertruck]

Yeah, I'm going to chalk this up to a possible loose lug, and probably more bad breadboarding.....I can't seem to recreate the problem effectively.

I ended up going with the build your own pedal close -> classic delay circuit.  I breadboarded it and it seems to work, however the audio output is very attenuated.....not sure whats that's about.  Back to troubleshooting.