I had to do some cap replacement on some older Motorola tube radios,I have some basic soldering skills. I was under the impression that the capacitors in computer equipment this big from this year would have been of better quality and it would not be an issue.
I have someone scheduled to come out tonight after i get off work and get it out of the rack. On Fri, Jul 17, 2015 at 3:45 PM, Brent Hilpert <hilp...@cs.ubc.ca> wrote: > On 2015-Jul-17, at 11:42 AM, tony duell wrote: > >>> It is generally a good idea to re-form electrolytic capacitors in power > >>> supplies, and to bench check the power supplies (under some kind of > >>> load) before actually applying power to the whole unit. > >> > >> It is always a good idea to replace electrolytic capacitors in power > supplies. > > > > Could you, please, explain why? And how often should this be done? Every > > week, every month, every year, or what? > > > > FWIW, the number PSU elecrtrolytics I have replaced can be counted on > the fingers of > > one hand -- in unary. Well, perhaps both hands. But it's <1% of all the > PSU electrolytic > > capacitors I own. > > > > Only 2 cases spring to mind : > > > > The PSU in my 11/44 had a high ESR capacitor on the +36V rail (all other > caps in the machine > > were fine) > > > > I changed the 2 mains smoothing capacitors in my HP120 not because they > were electrically > > defective (they tested fine) but because one was bulging a little on top > and had it exploded it would > > have hit the neck of the CRT with all the problems that would be likely > to cause. > > > > I do find this witch-hunt against capacitors to be curious, given how > few I've found to have > > failed. I suspect a lot of it comes from audiophools who think this is > the way to fix anything... > > This is something Tony and I are quite in agreement on. > > Similar to Tony, (and as mentioned in discussion on this topic a couple of > months ago): in the solid-state category, of the many pieces of 1960s & 70s > and later equipment I have or have serviced, the vast majority are running > with their original capacitors. > > If you're dealing with a 1936 or 1952 tube radio, a knee-jerk "replace the > capacitors" is warranted. > If you're dealing with a 1970s computer, it isn't (IMHO). Esp. when > they're screw-terminal 'computer-grade' caps. > > My own perception of the concern is that it has been perpetuated over the > years from the vacuum tube / antique radio arena. The issue of capacitors > "drying out" dates from the days (1920s,early 30s) when electrolytics > actually were filled with an active liquid which actually did dry up. > "Dry electrolytics" were developed in the 1930s, and while early dry > electrolytics also warrant replacement, the chemistry and techniques have > seen a few improvements in the many intervening years, and solid-state > equipment is not placing the same stresses on caps as tube equipment. > > In other arenas it's a real issue, in a modern arena it is largely lore. > > The point of electrolytic caps is to form an oxide to be the dielectric, > formed (in part) out of the electrolyte, and while I'm no expert on the > chemistry, I will point out the oxidised state is 'the' or 'a' low energy > state, and hence relatively stable. Rust doesn't normally undo itself. > >
