troubleshooting A12 (seventh circle)

Hi folks,

I'm posting this at the seventh circle forum too, but I figure I can use all the help I can.

I recently finished an a12 card, but the phantom wouldn't work. Doing the molex connectors, I may have very well shorted one a b+/- to ground, blowing a fuse. At this point it's been a awhile, so I'm a little hazy with the play by play idiocy of that day.

In any case, the card is powering up, and there's proper (+/- 18v) at the pins for the opamp (1122 Avedis), but when the op amp is inserted, things go wrong. Mainly, I get a pulsating, chugging bit of sound at the output. It definitely sounds the way a wave looks on a screen. I think. Yikes. And, the opamp (and the card in general from what I can tell) also starts to heat up.

The obvious novice reaction is blown opamp. Has anyone fried an opamp, and did have similar symptoms at any point?

I really can't wait to get this thing done, so I can move on to the SSL!!

Thanks for any ideas...and have a good Thanksgiving.

Kelly

I feel so bad that you have had so many problems with your A12s. A bad op-amp would be MY first reaction, but I'd sure wonder how it got that way.

Have you tested the voltages in the op-amp socket?

Perhaps you should test the other pins for any voltage (op-amp not inserted of course). It would be a tragedy if the phantom power got routed to one of those pins there! Test all of them referenced to common ground to see if there are any stray voltages coming in.

Also, you can test the continuity between any of the pins on the molex connector to see if the phantom lead shorted to another. There shouldn't be any continuity between any of the pins.

I don't think it's too likely that you've shorted the pins under the molex connectro because it'd take an awful lot of solder, and solder has a tendecy to stick to what's hot. If the adjacent pin isn't heated the solder won't have a tendency to want to go there. That's why you can solder pins very close together (like on the rotary switch) without worry.

Do you have another module you can try that op-amp in?

This IS the one you sent to Tim for repair right? I mean, at least at some point you knew the construction and operation was correct, right?

Good luck! ...and don't worry. If NASA can fix the hubble we can certainly fix your preamp!

Shane

Shane, you are a saint. I'm going to the girlfriend's for dinner right now, but I'm going to check all that you mentioned your post this evening.

I can't believe I'm still working on this thing. I'm not the smartest guy you've met, but... :roll:

Again, thanks so much. I'm learning a lot. I've been doing electronics reading and problems all morning...

kelly