SPQR's guide to upgrading your ZipGS
Firstly, this will void any warranty that may still exist on your Zip. That's
not too big of an issue, because I believe that everyone who offered a warranty
has gone out of business. Second, I've only done this on my own ZipGSX 1.02,
so I don't know what differences there are between this board and other
boards. I'm typing this up using my Zip'ed IIgs right now, so I didn't fry
the board... these modifications worked for ME. Your mileage may vary. I
take no responsibility for you messing up your own expensive hardware.
modifications are there to make?
Socket the Crystal
This was the first modification I did to my ZipGSX. Note that this is primarily
for people with Zips that use the 4 pin crystal, and not people with the
2 pin crystal... 2 pin crystals are much easier to solder and desolder,
and should definitely be soldered in.
Socketing the crystal serves no purpose other than to make changing the
crystal (and hence the clock speed) easier.
First, desolder the old crystal. There should be 4 pins. I found it was
impossible to get all the solder out, so I cut one of the leads and then
managed to wiggle the crystal out, by heating each of the still-intact leads
and moving the crystal farther away from the board. Next, solder the 14
pin socket in place. You do not need to solder all pins in; in fact, you
can easily get away with soldering in just the pins used by the crystal.
Of course, you should then stick with the same size (either full or half)
crystal. (A full size crystal will take up all the space on the 14 pin socket...
a half size will take up about half. Tricky naming scheme, isn't it?)
- 14 pin DIP socket, preferably Low Profile
Plug your crystal into the socket and power up. If you get the computer
to boot, you've done well. If not, check to make sure that the alignment
has been maintained... VERY important. Pin 1 is the "identified"
pin; it will have a square corner when the others are rounded, and there
may be a dot on top corresponding with which corner is pin 1. Pin 1 should
be at the top left. Still no dice, make sure that the crystal is fully seated
in the socket, and there is a good electrical connection there. Also, be
sure that the socket is soldered in properly to the Zip... if not, you may
not have a good enough connection to make things work.
74F00 -> 74HC00
Above a certain speed (12.5 MHz or so), the 74F00 chip is not fast enough
to keep up with the Zip... hence, the Zip stops being so zippy. The 74HC00
is a high speed CMOS chip, so it will keep up, and should have a lower power
consumption at lower speeds (and hence less heat being generated).
I found it almost impossible to desolder the 74F00. I recommend cutting
the 74F00 off (with a small cutter... snip the pins), then desoldering each
pin individually. The 74HC00 is a drop-in replacement, just keep the pin
alignment the same and solder it in.
Since the 74HC00 is a CMOS chip, you must be very careful about static.
It will destroy the CMOS chip, forcing you to do it all over again, and
be more careful.
Increase the Cache
Increasing the cache is the easiest and perhaps safest way to improve performance.
Note that 64k is the most cache you can install.
There has been much debate about what is the "best" speed SRAM
chips to install. I personally recommend the 15ns. I'm running on 15ns "skinny"
chips in both the TAG and DATA sockets, and it's fine.
I have located a source of 32kx8 SRAM chips! I can't guarantee that they'll
work, as I haven't tried them... but these are reputable people that I like
very much. Elek-Tek Search their product
index for "SRAM".
Another source is Chip Factory. Very
nice folks who gave away popcorn at Comdex. They expect COD payment + shipping,
but I believe the prices are a bit better. I wasn't told the speeds, but
I didn't ask, either... most SRAM is fast enough. (be sure to get 15 or
20ns, though.) It's a 32kx8 SRAM, 15 ns. Good luck.
If you're not going to increase your processor speed any time soon, you
can save a few bucks and get SRAMs of the same speed that you have now.
However, if you increase the speed later, you may find that you need new
SRAMs... faster ones. If that's the case, you're going to be out the cost
of the chips twice, unless you can sell off your slower cache chips. If
speed matters to you, get the 15ns chips. They'll serve you well.
The next problem is that the Zip usually comes with wide cache sockets installed
on it, and most of the "modern" SRAM chips are narrow. If you
can get chips that match your sockets, you're fine. Otherwise, you'll need
to either install new sockets or add in "half-sockets".
Note on selecting SRAMs: You can't mix and match 8k chips with 32k chips.
It just won't work; there's no way to tell the Zip what it has where. Your
choices are 8k, 16k, 32k, and 64k. To upgrade from 8k or 16k to 64k, you
need 4 32k chips. To upgrade from 8k or 16k to 32k, or from 32k to 64k,
you need 2 32k chips. To upgrade from 8k to 16k, you need 2 8k chips.
- SRAM chips (8k or 32k, 28 pin)
- 1 of the following:
- 2 low profile 28 pin DIP sockets (wide)
- 6 30 pin SIPP sockets
- 4 low profile 28 pin DIP sockets (narrow)
2 28 pin sockets
Half-sockets is the easiest option, however it's tricky. You'll need a hacksaw,
and you'll need to cut JUST THE SOCKET while it's still installed on the
board. If you flip the Zip over, you'll notice that there is a row of empty
holes in the middle of each of the cache sockets, wired in parallel with
the high-numbered side of the socket. That's where our new half-socket goes.
First, cut the middle "bars" out of the way on the sockets installed
on the Zip. This should expose the holes we're interested in. If there is
solder in these holes (probably), remove it. Cut the bars off of a low-profile
28 pin DIP socket. This will give you two "half-sockets". Solder
one of the half-sockets in the middle of each of the cache sockets. Now,
you can install either narrow or wide chips.
SIPP sockets is the most difficult, but most flexible and best-looking option.
First, cut each SIPP socket into 2 14 pin strips. Then, desolder all the
cache sockets on the Zip. Install the SIPP sockets into the holes where
the DIP sockets were, as well as the holes in the middle. This should allow
you to plug in either wide or narrow chips.
Only perform this modification if you will only be using narrow chips. It
prevents you from later installing wide chips without further modification.
First, desolder all the cache sockets currently installed in the Zip. Then,
solder in the narrow sockets. On the left side of eac socket, you will be
re-using the old holes. On the right side, you will be using the holes previously
concealed under the middle of each socket. This should look very nice, but
be very difficult to install, and with almost no flexibility.
No matter which socket option you go with, installing the chips is very
straightforward. Be sure that you're grounded when handling the chips. "Static
RAM" does not mean that the chips like static electricity. Just line
up the chips, and push them in firmly. The notch should be towards the top
of the board.
Split the Cache
Splitting the cache is a moderately difficult undertaking, the procedure
is described elsewhere. Usually, the Zip's cache holds both code and data,
intermixed. If more data needs to be cached than code, the code can be overwritten...
leading to a performance hit when the cache needs to be reloaded.
It has been my experience that desktop programs and compilers benefit most
from this style modification. To split your cache, you need to start with
either a 64k cache or a 16k cache (recommended is 64k.. simpler to modify,
and simpler to change back).
Change the Processor
If you need more speed, you'll probably need a faster processor. You can
get these from either Alltech in single-quantities,
or Western Design Center (the company
that produces these). WDC had a $100 minimum order last I checked, although
it can be waived for students, teachers, and the like.
Be sure and get the PLCC version of the chip.
WDC's web site lists that they have 16 Mhz 65816's available. I haven't
checked up on this, but anyone who talks to WDC should be able to find out
about it. Let me know...
Actually changing the processor is easy. You'll need the new processor,
and a PLCC extractor. Line up the PLCC extractor, squeeze it a little, pull
out the chip. Line up the new chip, push it in firmly with your thumbs.
Increase the Clock Speed
Increasing the clock speed is easier than changing the processor, IF
you've put the crystal in a socket.
If you haven't socketed the crystal, you'll have to desolder the old crystal
and solder in the new crystal every time you want to change the clock speed,
which could happen quite a bit if you're experimenting with the Zip, trying
to maximize performance.
If it's in a socket: unplug the old crystal. Plug in the new crystal. Keep
the alignment right... the dot should be at the top left.
If it's soldered: desolder and remove the old crystal. Install and solder
in place the new crystal. Keep the alignment right.
If it doesn't work.... you may be over-clocking the processor. This basically
means that nothing happens when you poewr up the machine. NOTHING happens,
that is. The screen won't even clear and put up "Apple IIgs".
Switch the crystal back to a lower speed one, and try again.
I recommend trying Digi-Key if you're
looking for crystals. They have either Full or Half size crystals, to match
whatever you currently have.
Add a Cache-Hit LED
Cache-hit LEDs are far more useful, I believe. They tell you when things
are going fast, not when things are going slow like the anti-caching LED
included on the Zip.
Also, for people with their computers running in PC-style cases, this may
be something to attach to the "Turbo" light on the front panel.
Simple add-on: you'll need one LED, I recommend green if it's going to be
inside the case, or whatever you have if it's on a PC style case.
You will be attaching the LED between the power and the anti-caching LEDs
already on the board. Solder the anode (long pin, or + side) of the LED
to the cathode of the Power LED. Solder the cathode (- side) of the LED
to the anode of the anti-caching LED. Power up, and it should flicker exactly
opposite of the anticaching LED. (note: there are four pins that the LEDs
are already soldered to on the Zip. We're interested in the two middle ones.
If your LED does nothing, you might have it backwards. Reverse the leads
and try it again.
LED pins (from solder side of board)
+O- <--- LED
+ - / \ + -
o o- -o o
Add an external Zip disable switch
This add-on is also for people with PC-style cases more than IIgs cases.
The best use I can think of for the Turbo switch on the front, is just that...
a Zip disable switch.
Close switch 1-6 (the Zip disable switch). Wire the leads from your switch
to the same pins used by switch 1-6 (pins 6 and 11 of DIP Switch bank 1).
Be careful not to short across any other pins with solder drips... it would
be VERY bad to have this switch monkeying with SW1-7, for example (the cache
size switch). Solder CLEANLY, with no drips.
1 o o 16
2 o o 15
3 o o 14
4 o o 13
5 o o 12
6 o o 11
7 o o 10
8 o o 9
The switch, when closed (pushed in) should close the circuit, as switch
1-6 did before, and make the Zip operate in fast mode. Opening the switch
should open the circuit, and make the Zip operate in normal mode (no acceleration).
This switch will not work to slow down things mid-application; this switch
only has effect at boot time and possibly after resets.
Getting More Power to the Zip
If you have a lot of high-power cards (say, a Zip and a RamFAST, maybe a
Second Sight), you may have experienced a few problems with your upgrade.
If it won't boot right at a higher speed than before, but when you drop
the old crystal back in, it works fine.... it could be a power problem.
Especially if you have a processor that is rated for the speed you're trying
to go. (I had a 14 MHz chip, and I was trying to run it at 12 Mhz. Worked
fine on the Rom3, but the Rom1 didn't work... But the Rom1 motherboard draws
uses more power for itself than the Rom3, so I thought it was a power problem.
Quite reasonable... I run a Sirius RAM with 6 megs, a RamFAST 'C', a Zip
12/64s, and a Grappler+.)
What will it look like? Well, for me, I was getting all sorts of strange
errors during the boot... things that just shouldn't be happening. Oddball
stuff, and then only partial error dialogs because there wasn't enough power
to load in the actual error messages. Let's just say that I was a little
concerned for the well-being of my computer.
A good test to see if power IS the problem is to turn off the Zip (1-6).
With CMOS circuits, the faster they run, the more power they draw. If disabling
the Zip helps, you've probably got power problems.
What do you do about power problems? Well, there are several solutions.
First, you can buy a high-output power supply. That may or may not work.
Why it might: more power gets supplied to the motherboard. Why it might
not: the motherboard circuit traces are only so big, and there's a finite
amount of power they can carry.
I'm still running off the plain, stock 60 watt power supply that Apple put
in the IIgs case. My solution was to beef up the power traces on the motherboard
by adding an 18 gauge copper wire (solid) between the pins of interest (+5V
on the power connector and +5V on the slot connector). If you have a lot
of cards, you may want to do this several times... once to each slot with
a heavy-hitting card in it.
First, pull out ALL the cards in your system. Put them in anti-static bags
if you have them. Otherwise, lay them (circuit-side down) on a large sheet
of aluminum foil. Disconnect all wires attached to the IIgs (monitor, disk
drive, joystick, ADB, printer, modem, etc.) Now comes the interesting part:
actually opening the IIgs case.
Pop out the power supply. There is one retaining clip for it in front. Just
pull on the clip enough so the power supply can move freely (up). Disconnect
the line cord and the connection to the motherboard. Put the power supply
Flip the case over. Near the front, you will see 3 little retaining clips
similar to the one for the power supply. Get in there with your finger,
push them out of the way. We're loosening the front panel (the little part
with the power light on it). Catch the front panel, set it aside.
Flip the case over again (now right-side up). You should see a bunch of
little retaining clips holding the motherboard down. Start next to the front
panel. Undo them all, while lifting up on the motherboard. Work towards
the back. When you undo the last one, it should pop loose into your hands..
and you're now holding a IIgs motherboard.
Flip the motherboard over. The pins you're interested in are pin 4 on the
power supply connector and pin 25 on the slot connector.
1 2 4 5 6 7
o o o o o o
Pin 25 on the slot connector is the one closest to the back, on the left
hand side (from the bottom). Left hand side... the side with the memory
card connector on it. Attach a wire running between the two pins, making
sure not to make your connection too tall (if it touches the metal on the
inside of the case, you'll have a short, and NOTHING will work).
To re-install the motherboard, line up the holes on the back of the case
with the connectors supposed to fit through them. Slowly work the motherboard
down. If it doesn't want to go, don't force it... back up, try again. You
don't want to snap your motherboard (check Alltech Electronics' page to
see how much a replacement would cost). When everything is aligned, one
firm push should seat the motherboard. You can put the front panel back
in by lining up the circular holes in the bottom of the case with the roundish
pins. Just push... it's done. Re-install the power supply, and the cards...
test it. If it works fine, you've done well.
If it doesn't work, make sure that
- The Zip ribbon cable is fully attached
- There are no short circuits (the hardware reference manual says that
the power supply will beep if there is a short circuit)
Good luck with your Zip GS modifications!
Feel free to let me know how things
work for you. Also, if you have any questions or suggestions. I want this
to be a valuable resource to the II community, not just something that a
few geeks check out once in a while.