Subject: FAQ-Zip GS upgrade: The 10MHz alternative
From: [email-masked] (Richard Der)
Date: Fri, 19 Jul 96 00:37:48 PDT
Newsgroups: comp.sys.apple2

You may be able to get it to run at up to 10MHz by just replacing the
oscillator with a faster one for less than two dollars!
 
I have a Zip GS that came as a 7/32 and was used at 7MHz for a long
time. The board came with a socketed oscillator, so one day I swapped
the 28MHz oscillator with a 36MHz one.  The computer booted up at 9MHz.
When the 36MHz osc was replaced with a 40MHz osc, the Zip ran at an
amazing 10MHz!
 
Your mileage may vary, though.  The GS that this upgraded Zip resides
has a high output power supply.
 
Still, considering these oscillators cost $1.39 each, it is worth
trying an oscillator swap alone first.
 
If a faster oscillator alone won't do the trick, then a faster CPU
and/or faster cache chips may be necessary.  The following are
sources for the parts (osc, CPU, and cache).

-----------------------------------------
 
Here's what you need to upgrade to 10MHz:
 
>From JDR Microdevices:
        Phone 1-800-538-5000
        Fax   1-800-538-5005
        BBS   1-408-494-1430
        Web   http://www.jdr.com
 
Get a TTL Output Oscillator rated 4 times the speed you want the Zip to
run.  For example, if you want 8MHz, get a 32MHz osc.  For 10MHz, use
a 40MHz.
 
You will actually probably need a 30MHz, a 32MHz, a 36MHz, and a 40Mhz
oscillator:
 
        Part #'s: OSC30.0, OSC32.0, OSC36.0, and OSC40.0
 
because you want to test the Zip to see how fast it will go.  It may
top out below 10MHz.  If it does, then you need a faster CPU and
faster cache RAM if you want 10MHz or faster.
 
---------------------------

You can get 64K's of fast cache from JDR Microdevices:
 
        Get 4 Static Cache RAM chips,
        Part #: HM62256LP-70
        Price: $4.69 per chip (you need 4 of these for 64K)
 
You can get a 14MHz fast CPU from:
        The Western Design Center       (http://www.wdesignc.com)
        2166 E. Brown Road              (email: [email-masked])
        Mesa, AZ 85213
 
        Part #: W65C816SPL-14 (for Zip GS or Transwarp GS accelerator
                               cards for the Apple IIgs computer)
        Price: $19.80 + $4.00 shipping & handling
 
        (Western Design Center requires payment by Money Order)

Once you get the cache chips and the CPU, remove the 4 (or 2) old cache
chips and plug in the 4 new ones, making sure the orientation of the
new chips is the same as the old ones were (you've just replaced slow
32K of cache with fast 64K cache).  Remove the CPU chip and plug in
the new CPU.  Finally, experiment with different oscillators, replacing
the original, and find the fastest one that works.
 
DIP switches settings have be changed when changing cache size.
There are two banks of DIP switches on the Zip card.
 
Switches 7 and 8 on DIP bank 1 determine the cache size. Bank 1 is
the bank of DIP switches nearer the top of the card.
 
The settings are as follows.

size            switch 7        switch 8
------------------------------------------
8K              on              on
16K             on              off
32K             off             on
64K             off             off

With a faster cache and 14MHz CPU, you may be able to go above 10MHz
by plugging in a 48MHz oscillator (for 12MHz Zip), or 64MHz oscillator
(for 14MHz).

Note:  Even if you need a new cache and CPU in addition to a new
       oscillator, you can still upgrade a 7/32 to a 10/64 and beyond
       for around $40. If you are satisfied with 10MHz and are lucky
       and don't need the new cache and CPU, then you'd get a 10/32
       upgrade for the price of a $1.39 oscillator!
-----------------------------------------------------------------------
 
Good luck.
 
(Note: The speed of these SRAMs will be sufficient to around 10MHz.
       The advantage of these particular chips are that they are
       available cheap and in the wide 600 mil package that the Zip
       sockets require.
 
       For 15MHz operation, even faster SRAMs may be required.
       Unfortunately, they are mostly available only in the skinny
       300 mil packages.  To use them, half sockets must be soldered
       into the Zip.  They are also more expensive.
 
       Also consider that the performance advantage going from 10MHz
       to 15MHz is far less dramatic than from 7MHz to 10MHz.  Factor
       in the risk of seriously damaging the Zip during soldering.
 
 Conclusion: the 10MHz operation is safer, requires no permanent
             modification of the Zip, and the chips of the right
             size are available and costs a lot less.)
 
Please distribute this document freely.  Apple II Forever.

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