Re: Daisy chained drives don't work

[Rubywand <rubywand@swbell.net>]

Rick Metheny writes ...
> 
> We've been working on resurrecting some IIgs machines and had a 3.5 and 5.25
> drive chained together and all worked fine. After a couple hectic weeks, we
> came back to the project and the drives all work individualy when connected
> to the IIgs, but none will work as the second drive in a chain.
> 
> Anyone with a clue what happened - or what we're doing wrong?
 ....

     If any standard IIgs Apple 3.5" drives are connected, they must be in the
chain _before_ any 5.25" drives. For example, with one standard IIgs Apple 3.5"
drive and one 5.25" drive, the 3.5" drive must be first in the chain-- i.e. the
drive connected to the IIgs Disk Port socket.

     The quickest, easiest way to verify that your GS Disk Port is okay is to
connect two standard IIgs Apple 3.5" drives followed by two 5.25" drives-- all
known-good drives.

     Be sure to connect or disconnect drives _only_ when the power is OFF.

     If all four drives work correctly, your IIgs Disk Port is okay. You will,
then, be able to say that something is wrong with the chain circuitry of any
standard IIgs Apple 3.5" drive which works but which does not allow connection of
any second drive. (Or, you could try out the suspect 3.5" drive(s) in a daisy chain
setup on a IIgs with a known-good Disk Port.)

 
     Otherwise, there are some checks you can make using different combinations of
drives. It may help to know that the Disk Port uses four signals to control the
drives on the chain: Drive 1 Select, Drive 2 Select, 3.5" Drive Select, and Head
Select. The 5.25" drives do not know how to deal with 3.5" Drive Select or Head
Select-- this is the main reason they must follow your IIgs Apple 3.5" drive(s) on
the chain.


     If you connect only a couple of 5.25" drives and the second drive will not
work no matter how the drives are connected, you very likely have a disconnected or
blown Drive 2 Select line on your GS Disk Port output. If both drives work
correctly, your Drive 1 Select and Drive 2 Select lines are okay.

     If a single standard IIgs Apple 3.5" drive works correctly, you know that, at
least, the Head Select line is okay; and, there is a pretty good chance that the
Drive 1 Select line is okay. If the drive does not turn on when, say, you do a PR#6
under DOS 3.3, you can be pretty sure that the 3.5" Select Line is okay, too.

     Suppose a 5.25" drive connected to the IIgs works fine but, when connected to
the above 3.5" drive, does not work. Most likely, the problem is with the 3.5"
drive's pass-through of the Drive 1 Select signal. If a drive was connected to or
disconnected from this 3.5" drive while the power was ON, this could explain the
damage done to the 3.5" drive's chain circuitry.




Rubywand