Help! Trident 80 Series, Exploding Caps

Hey guys,

After recapping and re-chipping the monitor modules on a Trident 80 Series I am experiencing some rather disturbing problems.

For starters I replaced all the chips with TL071CP's and all the caps are Panasonic ECG 22uf 35v & 100uF 25v.

The first three of the six modules function perfectly. The others keep blowing up the 100uF 25v caps.

I believe these caps are power de-coupling caps. On the schematic they are connected between ground & +20v and ground & -20v. Also one of the 100uf caps connected to one of the IC's keeps blowing.

I replaced all caps and chips according to the original Trident manual and component schedule. Also I tested the voltage at the edge connector and got +18 & -18.

Any thoughts or ideas would be greatly appreciated, as I have a session on monday.

Thanks a bunch

Pretty sure. I triple checked along side the component schedule and inspected each chip one by one. I spent all day doing this to all three modules. I feel like there must be something else.

Get a magnfiying glass and do a visual search. I would set one good channel on the bench next to one bad channel. Look at them, over under sideways down and I bet you will see something. Look for solder bridges.

Only thing I can think of is excess ripple current if ther polarity on the caps is right.

Or maybe the new op amps oscilate at high freq, causing the problem.

What kind of test equipment do you have? Scope?

I'm afraid I only have a digital multimeter, I could possibly borrow a scope. But I'm not sure what I'm looking for.

OK, set the voltmeter for AC volts and see what you read across the caps that are popping. Compare this reading between good/bad channels. This will tell you if there is a bunch of ripple on the caps that are popping. Do all 6 modules run off the same supply?

Can I test without the cap in?
It blows shortly after power is applied.

If caps are blowing that promptly they are either WAY overvoltaged or reversed. Wear safety glasses!

A quick check on overvoltage you can do with your multimeter---connect the leads with clip leads before power-up, and leave it on just long enough to get a semi-stable reading on the meter.

i had a similar problem w my old british console a few years ago, two exploding caps upon power-up, same cap in 2 adjacent channels. i can't remember which PSU leg it was but one was not working (+24, -24, 0). not knowing much about electronics at the time (still don't! but getting better) i took the PSU to a tech who rebuilt the supply. i still don't know if the limping PSU was the absolute cause of the caps popping but after rebuilding it i haven't had any such problems.

Blown up ´lytics sound to me like lots of AC. If these caps are B+ smoothing caps then you should check if the rectifier is still working.
good look
Jens