28 Jul
2009
28 Jul
'09
11:47 a.m.
On 28 Jul 2009 at 14:12, Joe Giliberti wrote:
It is very likely not a PSU fault. I wasn't sure
on this, but could
the PSU behave differently with and without load??
The 5150 PSU will not operate without a load. At least a diskette
drive must be attached. Unlike other later power supplies, the 16-
64K 5150 uses an AC fan, so it will keep running even though the
supply has shut down, so don't use the fan sound as an indicator of
anything.
If the PSU has measurable output (within tolerance of +5, +12, -5 and
-12) on all outputs with just a diskette drive load, connect the PSU
to the motherboard.
What wasn't clear from your narrative was the "Nothing at the ISA
slot" statement. Does this mean that you measured correct voltages
at the motherboard connector (with the motherboard attached) but not
at the ISA slot? If so, there's something really strange going on;
most likely a broken PCB trace or cold solder joint.
On the other hand if the output goes away when you attach the PSU to
the motherboard, you'll want to start checking for shorts. Quite
often, this is a motherboard capacitor gone bad. Your ohmmeter can
indicate which supply line is at fault.
--Chuck