17 Jul
2015
17 Jul
'15
12:58 p.m.
I was operating the panel when i first got it, now the numbers do not light
up, panel is unresponsive, and run light stays lit.(just describing the
behavior, i will not start it back up till I work on the power supply)
On Fri, Jul 17, 2015 at 3:50 PM, devin davison <lyokoboy0 at gmail.com> wrote:
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 <hilpert at 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.