I think it's contact cement, or rubber cement. It seems that heat, flux, and time are the enemies. It can also corrode circuit board traces.
Flux, even the "correct" rosin type, can be more of a problem than most people realize if not cleaned off after soldering.
I once had to repair a Perreaux SM2 preamp. The SM2 had completely blown it's power supply (in spectacular fashion). The kind folks at Perreaux (they really are very cool people to deal with) told me that sadly they had no spares for the custom made potted toroid transformer, but they did send me a schematic to aid me in designing a new power supply. NO, don't ask, I promised them it would not be distributed.:yes:
As luck would have it, an identical preamp popped up on the auction site, and it had one channel out. I figured I could easily swap power supplies, since a few of the semiconductors used are not to be found for love or money now. As luck would have it, for some reason I decided to at least look into the dead channel issue. Following a signal and checking voltages with my scope found a LOT of electrically isolated components, and simple continuity checks from one part to another confirmed.
On the bottom of both preamps, there was a large amount of old flux on each joint that had never been washed off (I'm not sure if Perreaux still does it this way, but these preamps were all hand-assembled). I would say roughly 50% of the solder pads were no longer connected to their traces due to the flux eating away at little exposed bits of copper between the solder mask and the solder pad itself. So, I went through the preamp board I bought online, and did a LOT of solder mask scraping and trace repair. That was all it took to get that preamp running happily again, so that board and power supply was installed in the customer's preamp.
The other board? All the King's horses and all the King's men are not putting that one together again....
WASH YOUR FLUX OFF!
:tresbon:
