[nSLUG] Re: SCSI novice, hardware qry

Mike Spencer mspencer at tallships.ca
Fri Mar 10 00:29:15 AST 2006

me> I'm having trouble getting a SCSI scanner to work: I can't seem to
me> talk to the SCSI card(s).

gnwiii> How is the SCSI bus terminated?  Some devices have built-in
gnwiii> termination that is switch selectable.

Ah, good point, George. That is the thing I don't really understand in
practical terms.

The manual for the scanner says, 

    Before connecting the scanner, check the documentation for your
    computer's SCSI port to determine whether a SCSI cable terminator
    is required. This will depend on the scanner's position in the
    SCSI chain and other factors. As shipped from the factory,
    Microtek SCSI scanners do NOT have internal cable terminators.

and the card manual says,

    A set of resistors called terminators must be either installed in
    or enabled on the first and last physical devices on each host
    adapter channel; otherwise, the devices will not operate
    properly. You may need to change the termination setting on some
    SCSI devices when you install them....

The cards have terminators in the proper places per the manual(s).
The scanner has no external switch or jumper for this and the manual
doesn't mention how to make the scanner terminal.  I suppose I could
take it apart and look for... Nah, doesn't sound promising, does it?
Well, maybe...

gnwiii> You can get external terminators that go between the cable and
gnwiii> the device.  If you have to purchase one, get an "active"
gnwiii> terminator.

Okay.  Good.  Goes "between the cable and the device".

    MoBo-> card -> cable -> external-terminator -> scanner

Doesn't make intuitive sense but I'll take your word for it.  I'll ask
at the local computer shops.

gnwiii> Try a different cable.  Cables are responsible for 70% of SCSI
gnwiii> problems...

Um.  Okay, odds favor that, then.  Don't have another cable.  Shopping

gnwiii> Maybe an interrupt conflict.  I think those are IDE cards.

IDE, yes.  But as far as I can tell with some groveling, it's not an
IRQ conflict.

gnwiii> How much is your time worth?  It is good that you have 2
gnwiii> cards, but you also need spares of the cable, terminator, and
gnwiii> a 2nd SCSI device for testing (I use an old SCSI CD drive).

As long as it's cold outside and in my studio much of the time, time's
cheaper than money.  :-) I must have 200# of assorted oldish computer
stuff but exactly 4 SCSI items of which 3 have to work or I'm stuck.
I guess I need to go on a scavenger hunt.

Thanks for the pointers, George.  I can get back to this with a little
more confidence.

- Mike

Michael Spencer                  Nova Scotia, Canada       .~. 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^


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