Re: 1.08 GB hard drive not working on IIgs... why?

[harold.h@genie.com (Harold Hislop)]

Myles,
 
The Apple Rev-C card has two "gotchas"...
1) It does not supply TrmPwr to the SCSI chain unless modified
2) It does not provide termination when used at one end of the chain
 
You have to use a short and good quality cable between the Rev-C and the
first SCSI device attached, further both the first and last device
attached must be terminated. (Best bet is to use a DB-25 pass-thru
terminator right on the Rev-C's DB-25 connector, then only the last
device attached should be terminated (as is the case with all the other
Apple II SCSI cards)
 
Many of the newer drives do not supply TrmPwr (optional under ANSI specs,
which also make clear that =at least= one device =must= supply this) Thus
many newer drives wont work on the Rev-C card (or Apple High Speed or CMS)
unless the SCSI card has been modified OR some other device on the chain
supplies this required signal (which powers the terminators at each end
of the SCSI chain)
 
You mention that "your ramfast hasn't arrived yet" so I would suggest that
you wait until it does, instead of making any mods... The RamFast has an
option to supply TrmPwr (jumper cap in place on Rev-D, SW #1 ON for Rev-C)
and it does supply it's own "head end" termination.
 
There are a couple of GIF's floating around that I drew up some time ago
showing exactly how to modify the Apple SCSI cards to supply TrmPwr... I
think they are available on "Grind" (and I =know= they're in the A2 library
on GEnie (totally shameless plug :)) If you want I'll email you the one
for the Rev-C Apple card.
 
Bottom line - Your symptoms are pretty much what I would expect with
incorrect termination and/or lack of TrmPwr.
 

--
-Harold Hislop
Hardware Coordinator,
Apple II RoundTable, GEnie
14Mhz/32k TWGS, 1Mb Rev-C RamFast, Prototype ROM_03 in tower
(Heritage Mac hardware also spoken (great IIgs peripheral ;))