29 Aug
2011
29 Aug
'11
5:45 p.m.
On Mon, 29 Aug 2011 17:34:59 -0700 (PDT), Mr Ian Primus
<ian_primus at yahoo.com> wrote:
You can just use a multimeter to check the resistance
of the power inputs
to ground, to isolate which rail is shorted out.
Yes, true. Though I don't know if it's a true short, or only low enough
resistance that it trips the PS's protection. Of course, knowing the output
currents of the PS, the voltage of the PS output in question, and the plain
resistance of the input on the mainboard, I could probably take a pretty
good guess.
I'd definitely start by yanking out the RAM. RAM
chips are common
failures,
and they're easy to plug in backwards too. Also,
check to make sure
nobody
plugged in the CPU backwards or something.
Right, I can give that a go. I doubt the machine's been physically confused
in that way, as the seller says that it was working when last powered up,
then failed on the next power up (a few years later). I do trust the
seller, but I'm also open to possibilities of that sort. Will have a close
inspect, reversed chips especially would be easy to spot. To be honest, I
do expect a number of failed 4116s as well. They seem to die randomly and
regularly. I should really try to buy a bunch of spares, but I've given up
on buying NOS and pulls from China. They seem to arrive jammed into chunks
of polystyrene with no anti-static protection, and very dead.
In most cases of shorted boards, it's definitely
possible to find the
problem without having to power up the board, by simply checking the
resistance between power and ground. Fortunately, all the chips on the
motherboard are socketed...
Yes - I think there might be one un-socketed IC on this board, but what are
the chances it'd be that one that was faulty? I think there are popular
laws that say the chances are about 100%, but I'm going to ignore them for
now.
Cheers,
Mike