A word about SI 9900's

[Lerxt]

Summary: Something you can do to improve the reliability of your 9900
Line eater: enabled

Hi there.  Since there's been a lot of talk about System Industries 9900
controllers here recently, I thought I'd mention a trick that I found
which could improve the reliability of your 9900 (and possibly other con-
trollers in the 9xxx series).

(Note: in performing the following procedure, it helps a lot if your
controller is mounted in a rack on rails so you can pull it out, and
high enough so you can get underneath it.)

The next time you bring down your VAX, go turn off the 9900 and slide it
out of the rack.  Get underneath it (or turn it face-up if you have those
fancy swiveling slides) and take the bottom off of the box.  These will
expose the controller motherboard, which is a massive, heavy board which
covers the entire bottom of the box.  There is a metal plate separating
this area from the rest of the box, with cutouts for the ZIF connector
pins (which interface to the machine and drive interface boards in the
top part of the box).

Notice how the motherboard is mounted.  In the 9900's that we have here
(they may have changed this, so yours could be different), the motherboard
is bolted to the metal plate at the front end, but the back end *isn't
supported at all*.  The pins for the ZIF connectors are located about
1/3 of the way back from the front end.  This means that these connector
pins, in addition to performing their electrical function, are supporting
most of the weight of the motherboard.  Now, this board is REAL HEAVY,
and the unsupported weight of the rear end of the board puts a considerable
torque on the connector pins -- enough to crack the board and lift traces
off in the area around the pins.

The cure for this is to take two small pieces of foam or other soft, non-
conducting material (the little foam blocks that they put in new mag tapes
work well), and place them at the rear of the box bottom so that they will
hold up the back end of the board.  Be careful that the foam doesn't touch
any unmasked traces.  This will take the stress off of the connectors, and
your 9900 will thank you for it.  A motherboard which is cracked in the
area around the connectors will generate all sorts of bizarre symptoms;
in one instance, I watched while an SI field engineer tapped on a damaged
board in the area around the connectors with a screwdriver handle, and
when he hit a certain spot, a CDC 9762 that was connected to the controller
*spun down* (and the 9900 isn't even supposed to be able to do that)!

If your controller is under warranty or service contract, consult with your
field engineer before performing this procedure (I can't imagine that they
would give you any argument about it, as long as they think that you know
what you're doing).  Generally, the 9900 is a pretty reliable gadget, and
together with a rack of Eagles, the average access time, $/MB and MTBF is
hard to beat.
---
It's been said by many a wise philosopher that when you die and your soul
goes to its final resting place, it has to make a connection in Atlanta.

Dave Cornutt, Gould Computer Systems, Ft. Lauderdale, FL
UUCP:  ...{sun,pur-ee,brl-bmd}!gould!dcornutt
 or ...!ucf-cs!novavax!houligan!dcornutt
ARPA: wait a minute, I've almost got it...

"The opinions expressed herein are not necessarily those of my employer,
not necessarily mine, and probably not necessary."