Apple //c & Disk II

[jd-wong@uxa.cso.uiuc.edu (Jim Wong)]

What exactly is involved in connecting a Disk II to an Apple //c?

A friend acquired a cable for that purpose a while back and ran into
some problems: after he connected the computer and the drive and
turned the system on, the machine's power light flickered and the
internal drive just spun.  After he disconnected the Disk II, he found
that the //c would no longer read disks -- in fact, it destroyed them.
Merely trying to boot from a floppy was sufficient to kill it.  Sometimes
only one track was destroyed, sometimes a number of consecutive trackes
were wiped out.  It looked like the drive was erasing whatever portions
of the disk the head passed over.

Based on a cursory examination of the system, it appears that he may
have plugged the cable into the Disk II upside down.

We've since acquired a replacement //c and, before we try connecting
it to an external drive, I thought I'd ask for some advice.

First, what is likely to have been damaged in the first attempt?  The
internal drive?  The floppy controller?  The Disk II?  Everything?

Second, how can you tell which way the 20-pin connector of the adapter
cable should be oriented relative to the Disk II?  The original Disk II
connector cable was threaded through a pair of what appear to be magnets
inside the drive housing.  Is it necessary to do the same with the
adapter cable?

Finally, what is the correct mapping between the pins of the connector
inside the external drive and the pins of the DB-19 connector at the
end of the cable.  I'm fairly sure the cable was wired correctly when
my friend bought it, but I'm concerned that he may have damaged it
in threading it through the magnets I mentioned above (it's a really
tight squeeze).  Is there anything to worry about, or are these
cables pretty durable?

Thanks for any help or information whatsoever.  I'd hate to see
another machine meet a premature end.
-- 
Jim Wong (jd-wong@uiuc.edu)