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ZipGS Upgrade

For about 2 years I have owned a 8/16 ZipGS.  I was happy with its
performance until I got hold of the IIGS Accelerator FAQ on Nathan Mates'
WEB page.
It all looked so easy that I wanted to try it myself.
I arranged for all the parts to come to Belgium.  no problem there.
Yesterday I upgraded my ZipGS to xx/64.
I installed it with a 60MHz crystal (15MHz) and booted.  Nothing happened.
I then tried it with a 55MHz crystal (13.75MHz).  Nothing happened.
I then tried it with a 48MHz crystal (12MHz).  Nothing happened.
I then tried it with the original 32MHz crystal (8MHz).  My GS booted
without any problem.
Did I do something wrong?
This is my configuration:
ROM 03 GS
   Slot 1   ProGrappler
   Slot 2   HS SCSI Card with 300MB HD, CD300e and 1.3GB MO
   Slot 3   ZipGS (used to be 8/16 now 8/64)
   Slot 4   SoundMeister
   Slot 5   PC Transporter Video (not taking up the actual slot)
   Slot 6   PC Transporter
   Slot 7   Empty
   Aux      Sequential Systems 4MB Card

Possible causes :
1. The ZipGS still has the T1, T2 and T3 set for 8MHz operation.  Should
this be changed?  It said nothing in the FAQ.
2. The SRAM used are Sony CXK58258AP-25 with 25ns access.  Quick
calculation says max. 40MHz or 10MHz clock.  But the FAQ says 35ns should
be OK up to 12MHz.
3. I changed the 74F00 to 74HC00.  The 74F02 I left, since it is not
mentioned in the FAQ.
4. The original crystal is a 4 pin TTL, while the replacement crystals are
all 4 pin 1/2 TTL (the Epson crystal from Digi Key as stated in the FAQ). 
Maybe there is some bad contact.  I will check this today.
5. Below spec 65816s.  Seems rather unlikely to me.

-- 
Woe to you oh Earth and sea for the Devil has sent the Beast with wrath.  Let him who hath understanding reckon the number of the Beast for it is a human number and its number is six hundred and sixty six.
Iron Maiden -- the Number of the Beast