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Expansion and upgrades are becoming more and more popular as knowledge about the internal workings of these machines continues to grow. I even accelerated my own TI-85 (original instructions by Boris Lutz and Keith L. Miller). I have re-done their instructions to be a little easier to view (they used all text. I have added graphics that illustrate the actual board's surface). Curently, the TI-81 and the TI-85 can be accelerated. (The TI-82 can also be accelerated, but it is a lot more complicated. The TI-82 intructions will come after the TI-85/81 instructions The TI-83 may be possible to accelerate like the 82, but I'm not sure yet. When I find out, I will post it here. All other calculators have not yet been accelerated.

TI-81 and TI-85

Step one is to open the calculator. To do this, take out the two screws at the bottom of the calculator. Then remove the battery cover and the batterys. Remove the screw that holds the back up batery and remove it (Some newer TI-81s don't have back up batterys. They have special memory chips that don't need them. They should work the same way as the other TI-81s). To pop the case, I have read that you can pop the bottom side open with a flat screw driver and run the battery cover along the side to pop it open the rest of the way. I usualy work the grooves out of the slots by pushing sideways on the case. You can use the method you prefer, but once it is open you will see a silver shield. Take out the two screws at the bottom that hold the shield on and then remove the shield. Follow by removing the two screws that hold the display board on (be careful not to tear the plasic conductor strip. If you do, you can cut off the damaged piece, scrape off the stuff from over the contacts, and solder wires between the display board and the main board). Once the display is out of the way, you will see the top of the main board. On the main board, between the Microprocessor (U4) and U6, you will find two capacitors and a resistor. The top right capacitor (very top capacitor on the TI-81) is labeled C9. This is a 22pf capacitor that has a part in regulating the clock speed. If you replace it with a 1pf capacitor, the clock will cycle about three times its normal speed! It has been said that simply removing C9 can also work to accelerate the calculator by 3.5 times, however, certain ROM versions might not operate properly. If you simply remove C9 and you occasionaly get lines across your screen that don't go away until you reset, then you will have to use the 1pf capacitor or return the 22pf capacitor. (press 2nd, Mode, Alpha, and S to see your ROM version. Do not press ENTER!!! It will erase your memory. Choose quit or turn off the calculator to get out of the screen).

There is also a way to switch between the two speeds. I recomend this method because there may be times that you won't need or even won't want the calculator to run at the high speed. The high speed mode can use up to twice the normal power, and with games, you might not be able to keep up with them. I installed a switch in my 85 and will tell you how to install one in both the 81 and 85.

First, cut two four inch lengths of wire. Get a small slide switch that you can fit into the calculator and a 1pf capacitor. You will need to cut a hole for the slide switch. I used a Dremel tool to make the hole, but if you don't have one, you could probably make the hole with a soldering iron and trim it with a small knife. Keith L. Miller's instructions say that the inside of the battery case, beside the back up battery is the best place for the switch. It is a good place, but if you're like me, you will switch speeds a lot. I did NOT want to have to open the battery case each time I wanted to switch speed. You could cut a hole in the battery case over the switch, but I decided to place the switch along the side of the battery case on the angled part of the case (see the picture for the possible locations of the switch).

You will need to de-solder capacitor C9. This is one of the more dificult parts of the procedure. The best way is to put light pressure on the side with a small screw driver while heating one side of the capacitor, then the other, and continue back and forth until it comes loose. You don't want to over heat the capacitor. If you do burn it out or lose it (it is small), you should be able to get away with using a 33pf capacitor in its place. Now, re-solder the bottom side of the 22pf capacitor to the top pad (left side of the capacitor to the right pad for the TI-81) Solder the two wires to the switch. One of the ends of the two wires should be soldered to the pad where the capacitor used to be, the other wire to the end of the capacitor. If you are using (and I strongly recomend it) the 1pf capacitor, you only need to solder it between the two wires at the switch. Tape down the two wires, trying to cover as few components as possible. Cut a small notch on the edge of the silver shield to let the wire pass easily through. The illustration below will show all the details of the wiring...

Once the parts are installed you can reassemble the calculator by screwing in the screen, the silver shield, and then snapping and screwing the case back together. Which ever method you choose, I hope it will go well for you. Good Luck!!!