resistor packs for terminating SCSI bus inside Exabyte 8020

[Nigel Johnson]

On 2021-02-06 8:51 p.m., Glen Slick via cctalk wrote:
> On Sat, Feb 6, 2021 at 4:33 PM Nigel Johnson via cctalk
> <cctalk at classiccmp.org> wrote:
>> I have some 4608X-104-221/331L currently in my digikey shopping basket -
>> I will place order on Monday after I confirm that the two outside pins
>> go to Vcc and Fss and the six others go to signal pins on the bus.
>>
> I pulled the SIP packs out of my EXB-8200 because it is mounted in an
> external case and the next time I go to use it I would probably attach
> an external terminator to it without thinking that it was terminated
> internally.
>
> I measured ~91-Ohm between pin 1 and pin 8, which is the expected
> value for (6x) (220-Ohm + 330-Ohm) in parallel.
>
> I measured ~163-Ohm between pin 1 and each of pin 2, 3, 4, 5, 6, 7.
> That is the expected value for 330-Ohm in parallel with (220-Ohm in
> series with 110-Ohm ((5x) (220-Ohm + 330-Ohm) in parallel).
>
> I measured ~145-Ohm between pin 8 and each of 2, 3, 4, 5, 6, 7. That
> is the expected value for 220-Ohm in parallel with (330-Ohm in series
> with 110-Ohm ((5x) (220-Ohm + 330-Ohm) in parallel).
>
> So a 4608X-104-221/331L should be a functional equivalent (220-Ohm in
> common to pin 8, 330-Ohm in common to pin 1).


Thank you, Glen.  I will order some from Digikey on Monday.  So it seems
that the manual is lying when it says it has seven resistors - I didn't
think that was likely - in that case you would need a a separate pack
for the other side of the pull and there are 3 - not an even number.

I also powered up the unit and checked that I have 5V on on eend and
ground on the other, so all looks good.

Thanks to all for your help,

Nigel


Nigel Johnson, MSc., MIEEE, MCSE VE3ID/G4AJQ/VA3MCU
Amateur Radio, the origin of the open-source concept!
Skype:  TILBURY2591 nw.johnson at ieee.org