CNISWONGER@SIMTEL20.ARPA (Mike Niswonger) (09/03/85)
**** 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
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