22 Oct
2007
22 Oct
'07
3:13 p.m.
I've never
worked on this supply (and don't have schematics), but it
can't be that odd, can it???
It's complex enough that I'd feel better going at it with a set
of schematics. If nothing turns up I'll draw it out myself, but
if someone has technical data it could save considerable time. The
second supply generates +5 and +12v which is applied
only to the second disk drive power connector. This supply
constantly starts and stops - with or without a load. I
can see the output voltages coming on, then going off
over and over.
Wouldn't it be best to find out why it's doing this? My _guess_ is that
either one output is rising too high, tripping the crowbar, and thus
shutting the supply down, or, less likely, the supply to the control
circutiry has failed (the reason I mention the latter is that that fualt,
caused by a dried-up capacitor on the _primary_ side of the supply, once
led me a merry dance in a Tektronix X-terminal). I'd be inclined to start
by checking _all_ the electrolytics on that second PSU board with an ESR
meter. An high ESR capactior on the output side can put some
'interesting' high-ish voltage spikes on the output. I too suspect a lack of regulation and crowbar trip,
and yes in the absense
of technical data, I'll probably "shotgun" the electrolitics in the hope
that I'll get lucky.
I would strongly recomend getting an ESR meter if you do any (not many,
but any) repairs on SMPSUs. It will save a lot of time...
-tony