Dying VaxStation 4000 VLC - help?

From: Tothwolf <tothwolf_at_concentric.net>
Date: Sun Nov 17 02:21:00 2002

On Sun, 17 Nov 2002, Mark Tapley wrote:

> Good so far? Any way to test those theories with my analog VOM? Should I
> order a new LM193 comparator chip instead of a pile of capacitors for my
> first soldering attempt on this machine?

Are the two fans on the side of the power supply running properly? These
systems don't have the best cooling, and tended to run a little hot
anyway. What type of hard drive do you have in the system? A 1" high SCSI
drive, especially the faster ones may generate too much heat for the small
PSU fans to cope with.

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.

> If I *do* need to pull the comparator, I'll need to take the mainboard
> out of the chassis. That'll mean removing 4 extremely nasty plastic
> rivet things. How do those suckers come out in such a way as to leave
> them intact? I wrestled with one for a while and got nowhere.

First you'll want to remove lower portion of the plastic shell. There are
5 screws on the bottom of the unit, and two clips on the front edge. The
plastic shell has some tabs that engage on the rear of the unit, so be
careful not to break them when you tilt it off when you release the two
front clips.

Next you'll need to remove the graphics board, which is mounted with two
phillips screws near the video connector. Once those are out, you can
*carefully* unplug the board to board connector opposite the video
connector. Getting the board out is still tricky, and you have to move it
just so in order to get it to come out.

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.

PS/2 model 30 systems have similar plastic clips, and also have a little
tool inside the system for releasing them. I think the clips are a little
larger, so I doubt the tool would work on the ones in the 4000 VLC, but
DEC likely sold a tool for releasing them.

> All that notwithstanding, the capacitors may get due process after all.

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

-Toth
Received on Sun Nov 17 2002 - 02:21:00 GMT