[rescue] Can't clear ESP interrups: Check SCSI Term, Power Fuse ??

[Greg A. Woods]

[ On Sunday, July 8, 2001 at 23:00:52 (-0400), Rebecca Ore wrote: ]
> Subject: Re: [rescue] Can't clear ESP interrups: Check SCSI Term, Power Fuse  ??
>
> On Sun, 08 Jul 2001, Greg A. Woods wrote:
> 
> > Note that if it is the fuse, and so long as there's no short on the
> > board or in the connector, then you can still provide termination power
> > from any/all other devices on the bus....
> 
> Does having SCA drives complicate things?

Maybe.  I don't know a lot about the SCA interface, though my guess is
that it doesn't normally offer termination power back to the bus.

I have some SCA->HD68 adapters that do have jumpers to enable
termination power though....

If I remember correctly the internal side of the bus in an SS5 is
terminated on the SCA backplane....  Whether termination power is
supplied from that backplane or not I wouldn't know....

> The drive and drive case work with the LX and not with either of two
> SS5's, so I don't think there's a problem beyond the board.

that is a curious situation...

It's possible the external terminator or conenctors, etc., are a bit out
of spec.

> The SS5 found an internal CDROM -- don't know if that would have
> failed or if the external SCSI requires a bit more of the system.

the external scsi connector is just an extension of the same bus the
internal devices are on.....

> I'll have to see about internal termination on the drive, then.

Do check that the drive in the drive case does not have its own internal
termination enabled -- it must not as that's what the external
terminator is doing.

If you can enable it to provide termination power though, that would be
a good thing to do.....

In general I've found it's best to provide termination power at both
ends of the bus -- that way you know the voltage is up to par at both
terminators.

You'd do best to have an active terminator (or even better a "forced
perfect termination" terminator) on the external case.  I've only ever
seen really really really cheap active terminators without the LED, and
I've only ever seen rare HD50 and DD50 passive terminators with LEDs, so
if you have one with an LED and which isn't explicitly labeled "active",
it's probably an active terminator none the less...

-- 
							Greg A. Woods

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