> I think the average lifetime may be longer for electrolytics, especially
> those made in the past thirty years. I have had decent luck getting 50
> year old capacitors alive again - but only if they are treated right. The
> best way to keep them happy is to reform them, treat them gently, and use
> them.
The other big point is that (in general) computer capacitors are standard
parts. A 5000uF capacitor in a DEC PSU is replaceable by a standard 4700uF
one, avaialbe from a dozen suppliers in the UK alone. OK, so it may not
_look_ original, but the machine still works.
[...]
> Always disconnect the power supply(s) and check them out first! For
> non-switching supplies, disconnect the output (no load condition) and use
Absolutely. This is not to protect the PSU, but to protect the rest of the
machine. An overvoltage on the 5V line can ruin _every_ chip in the
machine. It's at times like those that you are glad of the ROM backups :-)
Seriously, I _never_ power up a machine without first checking the PSU on
a dummy load. Only once was the supply faulty (and the 5V line sat at
about 8.5V), but none the less I do it. I seems sensible to make sure
you're not about to ruin a piece of history.
[...]
> For switching supplies, connect a decent load, as some units _need_ a
> load or they will break. Still ramp up the input voltage, but do it
Light bulbs make good dummy loads. I was suprised that my DEC PC04 tape
reader uses a 12V car bulb running off the 5V line - and it's still quite
bright. I guess car headlamp bulbs would be ideal for SMPS loads. You can
get 6V car bulbs in the UK, BTW, but I had to order some when I wanted
them
In general you only need to load the main output - the one it takes
regulation from. This is likely to be a 5V output, but check the
schematics to be sure. For example, the PSU in my DEC LA324 printer has a
36V main output.
> quickly - perhaps over just a few seconds (the supplies will complain
> about the low input voltage). I suppose the best thing to do is to power
> the capacitors out of circuit - probably too much work for electonics of
> this vintage.
It's not necessary to run up _every_ small capacitor. It may be worth
doing the big ones, particularly the mains smoothing caps in an SMPS.
> Tantalum capacitors are pretty bulletproof, and do not need this treatment.
Odd, I've had a couple of tants go short circuit with impressive results
(pop, smoke, small flame). No other damage, though.
>
> > Card edge connectors: corrosion is common, especially is stored in damp
> > places or contaminated by skin oils. Can be cleaned with the classic "Pink
> > Pearl" eraser. (Don't use the grey erasers - too abrasive!)
>
> I would not do this, unless it is followed by a cleaning with a solvent
> of some sort. Erasers do leave a residue, mainly in the microscopic pits
> in the metal.
I clean my edge connectors with propan-2-ol (available in spray cans from
Electrolube). It removes most dirt, and doesn't damage the card edge. I
never use abrasives near a computer...
> William Donzelli
--
-tony
ard12_at_eng.cam.ac.uk
The gates in my computer are AND,OR and NOT, not Bill
Received on Wed Apr 02 1997 - 21:18:14 BST