ACCELERATING THE TI-85 - By: Keith L. Miller Materials Needed: 1 TI-85 1 VERY small slide switch 1 1pf cap 2 4 inch small wires (the smaller the better) pencil soldering iron black tape small screwdriver (Phillips and regular) Opening the TI-85: There are three screws which need to be removed. Two right below the battery cover and the one that holds in the backup battery. Once the screws are removed, the case needs to be pried apart. To do this without marring your 85, first use the small regular screwdriver to pop the bottom corner up. Then take the battery cover and slide it along the side of the calculator. It will force the sides to pop open. I have found that this works best without scaring the 85's case. What You See Next: Now, you will see a silver shield covering the 85's circuit boards. Remove the two small screws at the bottom of the shield. Once the screws are out, you will see under it two circuit boards. To accelerate your 85, you will have to remove the two screws that hold the top board in place. Now, lift the top board up and move it out of the way. This is what you'll see: ---------- CC ----------------- ------------------ | | | | C9 | | | | | | R C | | | | | U6 | R C | | | | | | R C | | | U5 | ----------------- | | | | CCC | U4 | | | | | | | | | | | | | | | | | ---------- | | ------------------ How to modify the board: ----------------------------------- | | ---------- CC ----------------- | ------------------ | | | | | C | | | | | | | R C | | | | | | U6 | R C | | | | | | | R o | | | | U5 | ----------------- | | | | | | CCC | | U4 | | | | | | | | | | | | | | | | | | | | | | | | | | ---------- | | | | | ------------------ | | SW1 | --------------------------O----->O- Screw Hole --> O CCC | | CCC --||-- 1pf ------------------- | | First, desolder C9 completely from the board. | /--\ SW1 | NOTE: Be very careful as to not overheat C9. It | | | __ | will fry at high temps. If it does however, | \--/ |__|| you can simply replace it with a 33pf |-------------------| cap. | | | | | | | | | | Next, resolder the bottom side of C9 to the top pad | | | | | leaving the bottom pad open. | | | | | | | | | | Now, solder two four inch long wires to your | | | | | switch. It really doesn't matter which terminals | | | | | you use. Now, solder the 1pf cap to both terminals | | | | | on the switch where the wires touch (see diagram). ------------------- Solder one of the four inch wires to the top of C9(the part of c9 that hasn't been soldered to the board yet). Solder the other wire to the pad where the bottom of C9 used to be. I found it easiest to run the wires around U4 and then tape them down using black electrical tape. Just use small pieces of tape. Try not to cover any components on the board. Now, the electrical stuff is done. The only thing left is to mount the switch. I used a Dremal tool and cut a small rectangle out of the case just above battery compartment #4. This leaves enough clearance for the switch when the cover is replaced later. Place the switch in the hole, and make sure there is plenty of room for the switch to slide. I used a hot glue gun to secure the switch, but just about any type of glue should work. I don't recommend taping it in. It might wiggle loose and touch something. The last thing I did was to put black tape on the silver shield where the switch would touch when the case is put back together. I also cut a small square notch out of the side of the shield for the two wires to bend up from the board to the switch. Once this is all done, your calculator can run is turbo or normal mode. Switching in the middle of a computation or game will not effect the anything but the speed because there is always a cap connected. NOTES: If you can't find a 1pf cap, you can put two or more caps in series. You might want to bend the leads on the switch 90 degrees to help with the clearance when the cover is replaced.