13 Nov
1997
13 Nov
'97
4:35 a.m.
On Wed, 12 Nov 1997, Bill Yakowenko wrote:
where. And I was paranoid about using a
continuity-checker for fear
of putting voltage someplace where it could do damage. (Was that
being excessive?)
I've used a continuity checker on computer bits many times without any
damage at all.
You do need to make sure that your continuity checker doesn't give out
excessive voltage, though. I have a homebrew one that's limited to a
_maximum_ of 2V at the probe tips. A DMM should be fine as well. Take care
if using an analogue multimeter - ones that use a 1.5V or 3V battery for
the ohms ranges should be fine, but I'd not use one with a higher voltage
than that. Whatever you do don't use a high-voltage insulation tester.
I suspect the new HP logic DART would be great for this - after all,
that's what it's designed for. Haven't got one - yet - though.
On the other hand, it should be trivial to measure voltage of the Trk00
signal at the connector, and see if it was getting that far. Divide
and conquer - the first secret of debugging.
The Trk00 signal at the connector is (a) only enabled when the drive is
selected and (b) is an open-collector signal terminated (I think) at the
controller. So if it's high at the drive when the drive is deselected, the
controller cable must be OK. And you know the controller itself is OK.
As a first guess, trace the trk00 pin on the drive back to the chip that
drives it (probably a 7438 or similar). Look at the inputs to that - are
they ever in the state that would make the output active (low)? If so,
change the driver chip - I've had a number of those fail.
Thanks guys!
Bill.
-tony