HELP! what did I do?? Gristleizer build snag

[kingnimrod]

I just built an endangered audio gristleizer and it was working fine until last night, when I was fitting it back into the enclosure. I'm not sure if I mashed something the wrong way squeezing it in or what.

Plugged in, and nothing - indicator LED, which stays lit when the unit is plugged in, does not light up at all. The unit passes signal when switched to bypass, but not when switched on. I went through the board, reflowing all solder joints and checking for any unintentional bridges between solder points. Everything looked fine.

Then I took out my audio probe and started to trace the signal. The input, when switched on, leads the signal first through a 741 op amp. I hear my input signal at the input pin, but don't on the output pin, or any other pin on this IC.

As I am a novice builder, I have no idea what this means - not sure if the IC is fried, or if there's something further down the line that isn't working that would cause the signal to end there. If the IC is fried, is it OK to replace the Texas instruments chip with the op amp I can get from Radio Shack?

If someone can walk me through this I would appreciate it greatly. This thing was sounding great -- so bummed about this....

[artifus]

yes, it's safe to replace the op amp with pretty much any other. check datasheets - available online - for compatibility. beyond that, i'm not much help, i'm afraid. good luck.

*edit* if it worked fine outside the case, and the case is metal, check for shorts making contact with the metal case.

[Ben N]

Have you checked V+ to the IC?

[kingnimrod]

think I may have blown one of the input power diodes. fingers crossed...

[kingnimrod]

OK, so I found a blown zener diode where the power comes into the board - replaced that and the unit came back to life. Stuck it back in my enclosure and it blew the diode again within 5 minutes. I'm using a hammond aluminum enclosure and have tried to avoid having any of the components touch each other... but wondering what could be blowing this diode.

any thoughts?

[kingnimrod]

Seems like it does have to do with shorting on the enclosure. I thought I blew the diode again as the light wouldn't come on after a few minutes in the enclosure. Took it out and working OK.

Scratching my head, as nothing on the board itself is touching the case - just pots, switches, and a single grounding point wired from the board connected to the chassis. Wondering if I have my CV jacks wired wrong.

Has anyone here done this build? Would love to see a gut shot of one that works fine.

[kingnimrod]

I have to add, Todd @ Endangered Audio has been EXTREMELY cool and helpful in the troubleshooting of this build. I think I'm in the home stretch of getting this finished.

[kingnimrod]

just to follow up on this. After messing around with this build for a while, I ended up having to send the unit to EA for repair. Turns out that placement of your switches and jacks in these can introduce crosstalk if they are too close together. Just got it back today and having a blast.