31 May
2007
31 May
'07
3:56 p.m.
Dan, that's fine advice. But a capacitor is just a
capacitor. They blow. No reason someone shouldn't
replace one if that'll get their computer back up and
running.
The Tandy 2000 used a funky p/s that was prone to, I
think, one particular cap blowing. What can you do?
You could jury rig another p/s in it's place. But when
mine went (in 1989) I looked at the schematic, and
Incidentally, IIRC, the Tandy 2000 PSU schematic is reprinted in the 2nd
edition of The Art of Elecrtronics (!)
went to Radio Shack, then went to work. And I had my
computer back.
I guess p/s problems could be some of the WORST
problems to a computer. You could fry a number of
chips (but this is uncommon). You could always effect
Indeed yes. Hence my other comment to always test a PSU on a dummy load,
not on the actual machine. Certainly after repair, and IMHO if the
machine has not been used for a long time (for suitable values of
'long'). It takes a lot less time to do that than to replace whatever
chips have fried...
Most decently-designed PSUs have crowbar circuits to protect the rest of
the machine if the PSU goes crazy. Note I said 'most', not 'all'. For
some unknown reason the HP9815 and HP9825 (and of course the 9831 too) do
not have corwbars. In the former case, at least, the 5V PSU is a
step-dwn swirtching regulator from a 30V DC line. If that chopper
transistor gails, it takes out a lot of chips!
the repair, then run it under load for a few days or
a
week and see how it's doing. Not everyone keeps or
I think you'd have to be very unlucky (and have a fault develop by chance
after the repair) for a PSU to test fine (and regulate) on dummy load and
then have the regulation fail a dew days later. Haviong the chopper fail
after a period of running is not uncommon, but that, in most SMPSUs,
doesn't cause the outputs to go high.
even knows how to use test equipment, so sometimes
you
just have to go with what you know. There's not too
many people these days that can or will work on this
stuff, so what can you do but your best.
The fact that not many people will do this sort of thing now seems to be
to be a good reason for having to do it yourself ;-)
-tony