On Wed, Aug 19, 2020 at 4:16 PM B 9 <hacke...@gmail.com> wrote: > > Thank you, that's a good point that I forget. All capacitors are supposed > to have a finite service lifetime, right? > > Manufacturers rate capacitors at the *maximum* temperature (105°C), and > the lifetime doubles for every 10°C reduction in ambient temperature. I > don't think Model T's run very hot — has anybody measured? — so maybe we > can expect them to live quite a bit longer. >
Yes. For Aluminum electrolytic caps made in the '80s, we are well past the expected thermal aging effects; I suspect failures now are due more to moisture than heat, although moisture + heat makes this worse. > When I was in school, I was taught that *“Experience is directly > proportional to the amount of equipment destroyed.”* I have not yet > destroyed enough equipment by desoldering, so I'll probably hold off on > recapping. > With proper instruction, destroying equipment is not a vital part of the learning experience. But it's always good to learn from our failures. > For desoldering, dwell time should be low and temp should be high, right? > I've got a regulated iron, but the desoldering braid I got from Radio-Shack > is so bad, it might as well have been labelled "this is a poor solder > sucker, but if you pay money for it, you'll be one too!" > For "normal printed-circuit" work, there will always be a dwell time of ~1.2 to 2 seconds when desoldering. You absolutely want to give the solder time to melt fully before applying suction. Also - use suction when removing through-hole parts; braid is for cleaning pads, removing bridges, etc. The issues come up when you're running too much heat (2 sec at 340C vs 2 sec at 500C is a big difference) or when you're not working on a "normal" PC board (cheap phenolic [paper] boards - Atari XE are notorious for this). Much worse if you're attempting rework on a flex cable or something. > Do you know if the Tandy 200 had similar problems? > I've worked on only 2 Tandy 200s so far, but I would be inclined to treat them similar to the model 100 -- replace the key power supply caps only. -Josh >
