14 May
2007
14 May
'07
4:43 p.m.
Warren Wolfe wrote:
On Mon, 2007-05-14 at 09:32 -0500, Jules Richardson
wrote:
I had that sort of thing at the back of my mind - but a variac often seems to
come up when systems which have linear PSUs are mentioned. Like you say, it
seems highly dependent on the circuit in question...
The rest of the machine *looks* healthy enough;
once I've replaced the
electrolytics is there any good reason not to slowly run the system up on a
variac (rather than giving it full AC from the start)?
Yes, actually. By using a variac, you would not be eliminating
risks, you would be trading them. Any circuit which tries to produce a
specific power level or voltage would be forced to draw more current to
achieve that goal, thus risking burn-out of the active component or
components involved. Rather than running it up slowly, I'd suggest
using full power
through a circuit with a lower than suggested fuse. Be aware that this
call is of a theological rather than engineering nature.
That does perhaps seem a better approach, given the unknowns. I'll run the
supply up first with no cards in place. I'm not sure whether it's wise to give
it a dummy load or not... I suppose it is, purely from the point of view that
it might encourage anything in the PSU circuit that's going to let go to do so
when there aren't "expensive" boards in place.
(That in turn begs the question: does anyone with one of these calculators
happen to have the PSU test points / correct output voltages noted down already?)
cheers
J.