Switching power supply fry

[Magnus Danielson]

>>>>> "S" == Stopp,Gene  <gene.stopp at telematics.com> writes:

 S> Hey Chris,
 S> Watch out fer them switchers, ya look at 'em funny and they blow up. And
 S> once ya do that, there's little hope of repair, at least not as a
 S> time-is-money proposition....

 S> If you're trying to test it without a load, this might be what you are
 S> seeing. Most switchers need a minimum load in order to come up to their
 S> operating voltages in the first place. When there's no load, they go
 S> into some kind of "idle" condition.

This is due to the fact that some cursuit solutions tend to be
unstable with a low load. So, if you see this, it is a more gratious
way to deal with the situation than emitting the gray smoke on you.
I use a old Seagate ST-251 (40 MB MFM, wow!) disc as a start load on a
PC supply I use for driving a EH SmallStone (who said it was neat???).
Instead of a noisy harddisc like I do it, you can use a 15 ohm power
resistor (this is what IBM used back in the days) between +12V and
ground to achieve the same effect. 

 S> If you are using a test load, disregard the above....

 S>  - Gene

 S>  p.s. anybody know what the -5v is used for on a PC motherboard? Can it
 S> be left off for normal operation?

It is normally used for supplying -5V to the ISA contacts, but nothing
else. It is a rarely used thing.

Cheers,
Magnus