Re: burning smell
On Wed, Mar 26, 2003 at 01:46:04AM -0800, Daniel Dent wrote:
> On Wed, 26 Mar 2003, Hamish Moffatt wrote:
> > On Tue, Mar 25, 2003 at 08:31:14PM -0800, Daniel Dent wrote:
> > > On Wed, 26 Mar 2003, Hugh Saunders wrote:
> > > > I have some spare psu bits (including fan) do you recon its worth
> > > > replacing the fan? or just stick an alternative psu?
If you smelt burning, something's knackered. If you can't definitely
find out what burnt, replace the whole thing. Is the fan actually
knackered once you get the brooch out?
> > > Well, in theory its a bad idea to open up a PSU, what with
> > > the capacitors that can store lethal amounts of energy...
> > If you leave it for a few hours after disconnecting the power, you
> > should be safe. The power supply should have resistors to discharge the
> > capacitors when they're switched off.
It SHOULD have, but often does not. If it does, less than a minute is
all you need. If it doesn't, a few days might not be enough. So check
it with a voltmeter.
> Other methods include shorting the capacitors with a
> screwdriver. This is slightly crude however, and can result
> in the screwdriver being fused to the capacitor :).
>
> There are more elegant devices with resistors in them
> designed for discharging capacitors.
I generally solder resistors across the capacitors temporarily while
I'm working on it.
> I've never heard of PSUs having discharging circuits built
> in, though it would seem sensible.
Some do, most don't. The problem is that the value of resistor that
you need to discharge the capacitors in a reasonably short time is
sufficiently low in value to waste a significant amount of power when
running. Also PSU designers have a regrettable tendency not to realise
that resistors have a voltage rating as well as a power rating, so
even if they did fit discharge resistors they might well have gone
open circuit by the time you need them.
Pigeon
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