Dying VaxStation 4000 VLC - help?

From: Mark Tapley <mtapley_at_swri.edu>
Date: Tue Nov 19 06:53:00 2002

All,
        I didn't get around to the soldering last night. My wife informed
me that we were going to get up at 0400 so the kids could see the Leonid
meteor shower, so I decided to get to bed earlier. Glad I did, it was
spectacular.
        I did do some more probing around the mainboard.

>> <88W>...I'll probe around looking for a resistor connecting high end to +5V.

        I looked. It doesn't connect to anything nearby, and when I say
"doesn't connect" I mean completely open circuit to everything. Practically
every other connection shows at least *some* conductance to *something*.
Also, I noticed that the other pins from SMD's like this one have a little
trace running off to a microscopic little pit in the printed circuit board.
I assume this pit is where the conducting path dives into the innards of
the circuit board. There's no such trace and pit on the upper right
terminal of this device. I think it really is a no-connect.

        On the 6192: I misled you all, I think. My apologies. Although I
remembered the color as "orange", it's in fact a subdued burnt orange, in
contrast to the bright international orange of the tantalum capacitors.
Someone who didn't graduate from the University of Texas might reasonably
refer to it as a reddish brown. :-) Meantime, there is in parallel with it,
just as Tony predicted, a tantalum capacitor (bright orange, with a pip).
        One more piece of evidence: all the tantalum caps have, in addition
to the pip, a "+" printed on the circuit board near one end. There is *one*
exception to that, where the pip points toward the power supply and away
from the "+" on the PCB. It's over near one of the connectors on the back
edge (maybe the SCSI, or 25-pin serial? I forget, but will post good
directions if anyone wants). The "+" mark is not present on 6192's position
on the PCB.

1) Anyone with access to a 4000 VLC mainboard, would you mind checking and
confirming that *all* of the tantalums are supposed to have the pip near
the "+" (and hence one of mine is probably in backward)? Or wait for better
directions, and check just the one that's backward on my board?

2) What's the consequence of having it reversed? Is that cap. probably now
dead?

        Anyway, by now I'm pretty convinced 6192 is the lower resistor of a
voltage divider.

I did not find a feedback resistor for the comparator. It still could be
there, but I don't think it's very close by.

                                                        - Mark
Received on Tue Nov 19 2002 - 06:53:00 GMT