Bus Adapter for XY753 & other SMD disk problems

[Steve Jay]

In v8n64, Dan Davison (dbd%benden at lanl.gov), says that his mysterious
XY753 problems went away when he switched from a Dawn adapter to an
Ilimite adapter, which has the controller plugged driectly into the
backplane instead of at the end of several inches of PCB trace.  However,
he says you then have cables "buried in deep inside" the chassis where
they might short out or damage neighboring boards.

AnDATAco [10054 Mesa Ridge Court, Suite 102, San Diego, CA 92121] makes a
model ET1100 Bus Adaptor specifically designed to install XY753's in Suns.
It allows the XY753 to plug directly into the backplane, and has cable
clamps & a nice, Sun-compatible, brown end plate (with holes for the
cables).  This solves both the original problem & the dangling cable
problem.

By the way, any adapter which has long PCB traces can cause trouble not
only for the board using that adapter, but grief for the entire VME bus.
Those traces act as antennas injecting random noise onto the bus.

While we're on the subject of flaky disk problems, I'll mention two other
sources of weird SMD disk problems that have bit us.  Both happened with
XY753's, but they could occur with any SMD disk/controller combination:

1.  Bad terminator for the SMD A cable.  I have seen this on SMD drives
connected to lots of different computers.  Although the terminator is a
simple, passive, device consisting of only resistors, it seems to fail at
a remarkably high rate.  I've seen a lot of disk service folks routinely
carry around one or more extra terminators.  A bad terminator can cause
all kind of problems.

2.  Both the A & B cables have green ground wires at the drive end.  Make
sure these ground wires are firmly attached to the drive.  There should be
a grounding screw near the cable connectors.  A non-attached or loosely
attached ground wire can also cause flakiness.

Steve Jay                       domain: shj at ultra.com
Ultra Network Technologies	Internet: ultra!shj at ames.arc.nasa.gov
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