Date   : Tue, 06 Mar 1984 14:58:00 PST
From   : MMOON.ES@PARC-MAXC.ARPA
Subject: Re: Alignment of disk drives with DDD (Dysan Diagnostic Disk)

You certain that an alignment problem exists?  Do the drives perform the
same warm as they do cold?  Morrow's data seperator on my controller 
like most designs of two to three years ago-- uses a digital phase
detector which is temperature dependent to a very high degree.  This
information comes from the close analysis of a friend doing circuit
design for Western Digital.   Also, which DJ2D are you running?  The
memory mapped version, the I/O mapped version *without* DMA, or the I/O
version *with* DMA.  Many of the non-DMA, I/O mapped controllers had
layout errors on the board which were corrected via cut & jumper; my own
had, I believe, six jumpers, but one pair of cuts had been left out.
They turned out to be the triggers to the one-shots controlling the
write-gate window for write pre-comp.  Failure to make those cuts
eventually cost me the 1791 controller.  (Note that this board was
purchased as-is with my full knowledge that design problems could exist.
Very few if any of these were, to my understanding, sold without such
information provided.  Morrow enjoys my high regard.)  My friend from
Western Digital found the missing cuts & things seem to have settled
down considerably.

                       MMoon.es