Another Zip story...

[o9938156@wsuaix.csc.wsu.edu (mark lyon)]

I've been playing with a 14 MHz 65816 too for several
days now.  I've not been entirely successful, however.
After installing all necessary mods, the Zip would refuse
to run at 13.75 MHz.  The problem appeared to be with
the cache RAM (15ns ISSI chips), as the Zip would run
with the cache RAM set to 8K, but not anything higher.
I have read about people having similar problems, but no
solutions.  What I tried was shielding the Zip from 
noise, which I've heard ROM 01's have plenty of.

So, I wrapped the Zip in several layers of aluminum foil
(the thicker, the better) and connected the foil electrically
to the metal case of the GS.  The case and shield should only 
connect at one point, otherwise ground loop problems
may rear their ugly heads.  The foil must also be prevented
from shorting any connections on the card, which I
did by putting some heavy paper between the foil and Zip.
If any cards are installed next to the Zip, the foil also
cannot short these.  The extent of shielding necessary depends
on how noisy the computer is and how susceptible the various
components are to noise.  When I had just the cache ram chips
shielded, the computer would boot fairly reliably, but would
crash pretty often (no garble on the screen, just a dive into
monitor).  So I eventually wrapped the entire board in foil.
Of course the fingers that go in the slot can't be shielded,  
and where the cable leaves is also a hard spot.  
It would also be good if the shield can be made from as few
pieces of foil as possible.  Any place where different pieces
of foil overlap is potentially a weak connection.

This apperently solved the memory corruption errors, as I
can now run somewhat reliably at 13.75MHz, 64K cache.  I
say somewhat, because it still crashes fairly often.  These
errors seem to occur about once every 30 minutes to an hour.
They may be caused by overheating due to lack of ventilation,
or some completely different reason!

Anyway, if you have a ROM 01, this may help if you are 
experiencing similar kinds of errors.

Mark Marr-Lyon
o9938156@wsuaix.csc.wsu.edu