Dying VaxStation 4000 VLC - help?

From: Mark Tapley <mtapley_at_swri.edu>
Date: Tue Nov 12 10:40:00 2002

All,
        Help! My cute little Vax 4000 VLC appears to be dying on me.

* Is there a service manual on-line for this machine? Any suggestions on
where to get one? I want things like connector pinouts (to see if there's a
power-fail line, or some such, and what it's expected to be), expected PS
voltages, things like that.

* Is there someone near San Antonio with a working VLC that they don't mind
if I abuse for voltage measurements, etc?

        Description of failure:
1) last time I played with it several months ago, it failed to boot for a
while with the VRC-16, LK-401, and mouse plugged into the graphics card
(yes I had S3 set correctly, because it later booted that way). Problem
went away, and I assumed there were intermittent problems with the graphics
card. (I'd never seen this with a console plugged into the MMJ).

2) Yesterday, it booted and ran for 2-3 hours with the VRC and kb. I
happily assumed the "graphics card problem" had cured itself. I logged in,
registered my Hobbyist licence, and started doing same on another (Alpha)
machine. After a while, my wife came in and started fooling with HELP on
the VAX. She hit 4 returns in a row, and it went dead (screen black). Tried
re-start, no-go. Got rid of the VRC-16 and LK-401, plugged in the VT-320,
reset S3. It *tried* to boot, but failed.

3) now, left power-on, the 8 LED's are on most of the time. Occasionally,
they will flash patterns, and the console will show the initial banner and
start the memory test. *Very* occasionally, it'll get as far as the
chevron. This morning, after being off all night, it got to the chevron,
accepted the "b dka100" command, and got about half way through the boot -
then the 8 LED's came on and it was back to ground zero.

        Tests run last night:
Pulled one and then both banks of RAM - no change.
Pulled the graphics card - no change.
Disconnected power and SCSI cable to hard drive - no change.
Reseated all (4) socketed chips (maybe ROM and the Dallas time module?) on
        the motherboard. - no change.
Did some measurements (details available) that make me think that 12V is
        actually about 11.5V, and 5V is actually about 5.1V. Gotta confirm
this,
        my only tool is an old Radio Shack Archerkit analog, and I want to try
        it on a known voltage source.
Tried to turn on without PS connected to motherboard (accidentally). Green LED
        on power supply board flashes, PS board makes crowbarring kind of
noice.
        (Green LED is otherwise on steady starting about 0.5 sec. after switch
        closes until switch open).

In the above, "no change" means LED's stayed lit - I didn't run long enough
in any of those configs to see if it'd try to boot after a while.

Power supply appears to be a switcher - lots of heavy heat-sinks on
transistors, lots of diodes, dozens of resistors. Multi-layer PC board.
There are several electrolytic (I think - cans, black wrapping over a
silver-looking can) caps, as well as some other types I don't recognize.

System is in pretty clean condition; I did not take out the motherboard but
cleaned the visible side of it with a brush and IPA. The only real dirt
accumulation was near the fans. No change.

I obviously had it fairly far apart last night, so I was extremely pleased
to see it start to boot this morning - disassembly by me is usually the
death of a system. This one is nice to work on, mechanically. But it's
still not running.

I'm on digest mode on the list, so I'll be slow at replying unless you hit
me at mtapley_at_swri.edu. Even then, I'm having minor email issues so there's
often a couple hour delay. But I'll sure appreciate any help!

                                - Mark

PS: On Friday, I said (WRT big auction of DEC parts)...

>...I don't think I need any parts now.

The irony is not lost but not particularly appreciated :-(. But the
question is which parts.... I'm tempted to just haul off and order a new
power supply - I'm pretty sure I can board-swap that without killing
anything.
Received on Tue Nov 12 2002 - 10:40:00 GMT