On Saturday, April 5, 2014 7:22:12 PM UTC-4, William Sommerwerck wrote:
I believe we recently had a discussion about an unsoldered ribbon cable that

had managed to make "acceptable" contact for many years, until...



I just had two "bad soldering" experiences that might be of interest.



Case 1: Both of my JVC XP-A1000 hall synthesizers had leaking power-supply

caps. About two years ago I replaced the caps in one of them. Then, six months

back, I replaced them in the other.



The second started having problems with oddball noises in the rear channels,

including some that sounded like idle noise. They came and went. I finally

ripped into the unit, and unsoldered my suspicious-looking joint on the

negative side of one of the caps. The pad came loose! I used a piece of heavy

solid wire to restore the connection. Et viola, the noise stopped.



Case 2: I hadn't used my Fosgate Tate II 101A SQ decoder in some years, and

tested it for a project I'd planned. The decoding was all shook up. This

looked bad, because the custom Exar chips used for logic control are no longer

made. In fact, they went out of production before the initial product run of

the Fosgate unit was completed, 30 years ago!



One of the designers told me how to confirm that the logic chips were okay.

They were (big sigh of relief). This left the phase-shift networks, which have

1% caps that can (supposedly) drift. Not only are the caps expensive and hard

to obtain, but unsoldering them runs the risk of destroying the foil.



The designer urged me to test the circuit's behavior (with a 'scope) before

unsoldering. This really required a schematic -- but harman\kardon had

destroyed all the schematics when it bought Fosgate! So I had no choice but to

trace it out, starting with a close-up photo of the foil side.



Some of the solder joints didn't look so hot. I resoldered them. Need I go

further? The unit is now working correctly.





"We already know the answers -- we just haven't asked the right questions."

-- Edwin Land

I've repaired many intermittent units over the years by "wholesale" re soldering anything that looked suspicious. I may not have found the problem but I fixed the unit. Lenny