EH Mini Q Tron problems...

[Phoenix]

Hi everyone, new here.

I've got an Electro Harmonix Mini Q Tron that is not working, and I haven't been able to figure out why.
I've done continuity testing on all of the solder joints, tested most of the component values, checked the supply rail voltage on the 3 TLC2262CP IC's, and so far everything seems to check out. Playing with any of the knobs or the internal trim pot doesn't seem to do anything.
When I put signal into the input, I don't seem to get any voltage swing. This doesn't surprise me because when I tested the DCR across the input, it is less than half an ohm, near enough to a dead short. When I test the load resistor in circuit I get the same reading, but when it is disconnected, I get the proper value (2.2M). I've been trying to track down a short in the circuit, but I can't find anything.

I don't even know if I'm using the right terms. I'm a tube guy, SS stuff is like a foreign language to me. I'd appreciate any help or suggestions.

[Phoenix]

Oh, by the way, I should have mentioned I'm not getting any signal through it at all. I get hum out the other end if I probe any of the inverting or non inverting inputs on any of the IC's though.

[StephenGiles]

Have you checked the connections from jacks to PCB

[Phoenix]

Yes, all connections are fine.

[Mialbu]

Hi Phoenix,

I had a problem with mine a while back. 
Turns out some of the soldering on one of the pots was a bit dodgy and when I repaired that, the pot turned out to be dead.

Have a look through the post:

http://www.diystompboxes.com/smfforum/index.php?topic=73191.0

Stick with it......the wealth of genius on this forum helped me to get mine up and running!

[Phoenix]

Thanks Michael,

I've checked the pots already, they're working fine. I've tested their sweep not just at the solder lugs, but further down the circuit path on the pcb, and they're definitely working. They were soldered pretty poorly though originally.

I've also tried replacing the IC's, I didn't have any TLC2262CP's available locally (I've got some on order), but I substituted TL072's in their place. They have the same pin-out and similar specifications and operating ranges. I don't believe that the originals are bad (although I have no idea how to test this), based on the fact that if I probed any of their +/-inputs I would get hum on the output.

I suppose it would help if I drew up a schematic and posted voltages, however as I've already named the brand and model, would that be a problem? I suppose it shouldn't be, as the model has been discontinued.

Thanks for the suggestions so far!

[Phoenix]

Hi everyone,
Just wanted to let you know that I found and corrected the problem. 
After removing and testing nearly every component on the board, I finally discovered that the input jack had a short between tip and sleeve. For the life of me I can't figure out how this happened. The jack was wired correctly, and I couldn't see the short by visual inspection, there was no sign of physical damage to it at all. 
After all that, I feel like a bit of an idiot, but glad I figured it out!

Thanks for your help and suggestions!