Date   : Mon, 02 Sep 1985 20:02:53-MDT
From   : Mike Niswonger <CNISWONGER@SIMTEL20.ARPA>
Subject: CCS 2422 Hangup Fix

           ****  5" / 8" Hangup Fix for CCS 2422  ****

     This information originally compiled by Joe Wright at  Alpha 
Systems - the creator of Z3-Dot-Com.  Joe found the hardware bug, 
and contacted CCS;  they acknowledged that they knew about it and 
took  Joe's  fix.    However,  this  information  never  got  any 
widespread distribution so here it is:

     The  CCS  2422 disk controller has a problem  switching  the 
1Mhz  and 2Mhz oscillator inputs to the WD179X  controller;  this 
appears  to  the user as an occasional lockup of the  board  when 
both  5"  and  8" drives are active.  The only way  out  of  this 
condition  is  to reboot the system (often not a  very  promising 
alternative).  The  problem is that the standard  board  switches 
freqs  on  the wrong edge of the clock.  This can be remedied  as 
follows:
  
     1)  Isolate  the clocks to U38 (pins 3 and 11) so that  they 
are  no  longer clocked by the RCLK signal,  but make  sure  that 
there is still a path to U8 pin 26 from U18 pin 9.  On the Rev  B 
baords  (and possibly others) this can be easily done by  cutting 
an  etch below U38 where the signals to pins 3 and 11 combine and 
go  through the board.   By making the cut at the correct  place, 
you can reduce the number of necessary jumpers to two.

     2)  Run  the  1Mhz signal from U15 pin 12  through  a  spare 
inverter  at U28 pin 9 (or any other spare inverter) and take the 
output from U28 pin 8 to U38 pins 3 and 11 (the clock inputs just 
isolated).

     Since  this mod requires a little cutting and pasting on the 
PC  board,  it is not for the weak at heart,  and  neither  Alpha 
Systems  nor  myself (Mike Niswonger) can be responsible for  any 
damage done to the system by improperly done mods.   This mod has 
been running on at least three systems for anywhere from 2  years 
to 3 months, with no known problems.  

     For further information on CCS S-100 boards,  drop a note to 
CNISWONGERill be glad to share  any  experiences 
both  good  and  bad.   In  addition,  I will try and  act  as  a 
clearinghouse for any other contributed CCS bug notes and  fixes, 
since we seem to have been abandoned by the company.

                                   Mike Niswonger,
                                   CNiswonger@Simtel20
                                   09/02/85