SCSI chains, quick question...

Ed Fletcher ed at
Sat Mar 5 05:24:54 UTC 2005

Vincent Trouilliez wrote:
> Problem: I have got a SCSI scanner, and an internal SCSI CD writer. 
> I got the scanner first, 9 months ago, it was working fine. 
> Then I removed it. Then later I was a given a SCSI CD writer, which
> worked fine.
> But today, for the first time, I tried plugging both the CD writer and
> scanner at the same time.  But at boot, the SCSI card (common Adaptec
> 2940 affair) times out when trying to detect the devices. CD writer
> alone no problem, scanner alone no problem, but both at the same time,
> times out, nothing detected ! :-/
> I very vaguely (probably wrong), that when you have both internal AND
> external devices, then the terminator must be placed on the external
> peripheral ? Or did my brain invite this during some bad dream ?
> So I tried that :
> internal CD writer : ID 2
> scanner : ID 3
> terminator : on the scanner.

Just going from memory here, but isn't there a setting in the adapter 
that allows you to disable an internal terminator?

I've got an old Adaptec AHA-2842VL that I no longer use.  IIRC, all the 
settings (including onboard termination) were controlled via the cards bios.

An onboard terminator would be in the middle of the scsi chain and give 
you the symptoms you're describing.

Ed Fletcher
ed at

What difference does it make to the dead, the orphans and the homeless,
whether the mad destruction is wrought under the name of totalitarianism
or the holy name of liberty or democracy?  -  Mahatma Gandhi (1869-1948)

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