On Fri, 29 Dec 2006, LarryT wrote: > My CC Amp died a while back & I thougt I;d try to resolder the CC Amp on > my '78 240D - But I'm not ready to change the capacitors. Which ones do I > buy? Does Radio Shack carry them? > > Also, the mechanics of resoldering the joints of the amp - I assume I > touch the soldered connection until it loosens and then solder it back?
I dont know if (and would be suprised if) Radio Shack even lists any electronics components any more. I bought some high temp/long life ones from digikey or mouser when I did mine... The value of the caps may vary by design, but the problem ones are the electorlytic types and on the CC's they are generally axial lead ones. In THEORY it is a matter of touching the joint and reflowing the solder. In practice: The PCB's are made of a phenolic material (as opposed to fiberglass), phenolic is MUCh cheaper but is mildly hygroscopic. This is dealt with by putting a "conformal coating" (ie varnish) on the PCB's, both sides, after the things are complete. The original solder is pretty crappy crap. You will need to strip off the old coating on the solder side. Varnish stripper removes it well enough. paint it on, wait for the stuff to bubble then rinse it off under cold water. Shake it off good and hard and let it air-dry overnight. Because of the crappy solder, and any varnish residue, you want to remove the old solder. You dont need a desoldering station or wick, I just used a soldapult/solder sucker to do the job. You then use NEW good solder to redo each and every joint properly (I prefer kester .032 63-37 for DIP/transistor PCB's). You need to work quickly at desoldering so as to not toast any components. You should let the part cool before resoldering IMHO. I will mentally divide the board into sections then desolder that section, then go back and resolder it. After you are all done, hold the board up to a light and you should not see ANY light through any of the holes where you have solder joints. If you see light, remove the solder and redo it. I tried reflowing the solder, then tried adding fresh solder, and no matter how many times I tried I kept getting joints that passed light (failed visual inspection), so they were either electrically bad or going to go electrically bad. I finally got PO'ed enough to figure &*^* it and went and desoldered it all and resoldered it and the pinholes went away. Oh yeah you should probably swap out the caps while you have that region desoldered ;) be careful not to lift any pads or traces. After all the joints are good, then you need to re-coat/seal the board to keep it from absorbing water vapor over the next 20-30 years... I used a proper flux remover [for the type of flux compound used by the solder that I was working with] to clean any residue off the board and then put a new coating on it. (2 light layers) Worked like a charm. Showed my wife how it saved a couple hundred dollars. I should probably go do the same thing for the 85 300d. Oh yeah, you should not need more than a 25 watt iron (period) for that job. I htink i used a 12 or 15 watt pencil. -j.
