Dying VaxStation 4000 VLC - help?

From: Mark Tapley <mtapley_at_swri.edu>
Date: Sun Nov 17 21:07:00 2002

Tothwolf asks:

>Are the two fans on the side of the power supply running properly?

Both still seem to be. However, most of the tests I'm talking about are run
with the lid off, and a small floor fan set up to blow over the mainboard
(in the same direction as the small cooling fans). I think the airflow rate
from this is much higher than the cooling fans would generate, but may not
be in the right areas.

>What type of hard drive do you have in the system?

1-Gig RZ26L.

>Your mainboard may have a bad solder joint somewhere near the comparator,
>which would explain the thermal issue. That tends to be the worst type of
>problem to pinpoint too.

It would, but unless the comparator or one of the voltage-divider resistors
is intermittent, I'm at a loss to explain the varying voltage on the
comparator input. I have physically shoved back and forth on all 3
components while it was running, no effect. Also I can't *see* any bad
solder joint, but then I can barely see the two resistors anyway.

>First you'll want to remove lower portion of the plastic shell. There are
>5 screws on the bottom of the unit,

5 holes, only two screws left in mine. I should probably get some more
screws, when I get everything put back together.

>and two clips on the front edge.

I see them. The plastic has to deform a log way before it'll release, but
I'll try it tonight.

>Next you'll need to remove the graphics board,

Yeah, that is tricky. Done it a couple times during earlier testing. The
problem first appeared when I was first using the graphics board, so I
blamed it. But I think it's working OK. At least for the moment, I'm doing
all the testing with a VT320 on the MMJ console port, so I have to
connect/disconnect less stuff when taking things apart.

>Once the graphics board is out, there are 3 more phillips screws at the
>back edge of the mainboard. The plastic clips pull up to release, but with
>the bottom shell off, you can use something to push them up from the
>underside.

Ok, that's a big help. If I can get the shell off I'll try poking them out.

>Certainly make sure they are discharged before you remove them, if you
>decide to replace them after all ;)

Ok. Short through a resistor for a minute or two? But I'm thinking right
now the comparator is the first target for replace, followed by the SMD
resistors if that doesn't do it.
                                                                        - Mark
Received on Sun Nov 17 2002 - 21:07:00 GMT