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?)
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.
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.
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.
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.
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).
If you're ready for more information on split-cache Zips, click here.
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. That's it.
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.
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 power anti-cache
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.
TOP 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.
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 aside.
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.
Power supply: 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
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.