Accelerate the TI-89


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Accelerate the TI-89



I don't plan on doing this, but have any of you out there tried this
interesting modification?

http://www.stud.ee.ethz.ch/~blutz/TI89Spec/TIAccelerate.html

Is the address for the site I found this modification on.
Title: Accelerate TI-89

Accelerate the TI-89

© by: Boris Lutz (blutz@stud.ee.ethz.ch)


Material Needed:

Optional:

 

Introduction:

I replaced the capacitor C10 (47pF) which is responsible for the speed with a smaller one (10pF). This makes the TI up totwo times faster!! The accelerated version of the TI-89 needs a little bit more power of a regular TI-89.
The best method to be able to change the speed is to use a variable capacitor. You would be able to change the speed continuously and play Assembler games at a reasonable speed.
I accept no responsibility for this procedure and any damage that it might cause, but if you follow my guidelines it works perfectly!
Don't use a capacitor with a capacitance below 20pF, this won't be stable!
The procedure described on this page is for the TI-89, the procedure for the TI-81, TI-82, TI-83, TI-85, TI-86 and TI-92 you can find here.

Opening the TI-89:

First make a backup then remove all batteries. There are seven screws which need to be removed. Two right below the battery cover, 2 above it, two at the top and one that holds in the backup battery. Once the screws are removed, you have to take off the bottom part of the case.
To do this, 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.

            Enter-Key                        F-Keys
           ________________________________________
          |        
          |------>---->---->---->---->---->---->---
          |     \                             /
          |______\___________________________/_____
                  \                         /
                   \                       /
                 Open here          slide until here      (on both sides)

Where is C10:

After opening the TI, you'll see a silver shield covering the TI's circuit board. Remove the two small screws at the bottom of the shield.
C10 is on the right side of U5 if the the display is at the top.

                   +-----------------------------------+
                   |                                   |   C
This plan shows    |                                   |   1
an enlargement     |                                   |   0
of the part of     |                                   |   
the TI-89 board    |                                   |   R
around C10.        |                                   |   1
                   |                U5                 |   2
                   |                                   |   
                   |                                   |   R
                   |                                   |   1
                   |                                   |   1
                   |                                   |   
                   |                                   |   C
                   |                                   |   9
                   +-----------------------------------+
 

Modifying the board:

First desolder C10 from the board. Be careful: Do not overheat any part!! Now you put the 20pF capacitor where the old C10 used to be.
Some TIs might work with a capacitor below 20pF, however this won't work on all TI-89s and is surely not as stable as a 20pF.
That's it, put back the shield (be sure, that it's position is properly adjusted), fasten the black plastic cover with the screws and put back the batteries (the four AAA batteries and the backup battery).

Just removing C10 or implementing a switch, like described on my TI-85 acceleration page is not recommended! Why: Just removing (without putting in a new capacitor) the capacitor will cause the TI-89 to freeze. (you have to reset it) Implementing a switch is more difficult with the 20pf capacitor, you can't connect the 20pf and the old capacitor in series (you would have a capacity of about 14pf and that's not enough, this would cause some errors)
To use a switch you would have to use a 35pF capacitor connected in series with the original capacitor and the switch over the 35pF capacitor (when the switch is closed the 35pF capacitor is short circuited).

A second possibility is to use a switch which connects the 20pF capacitor directly to the board and in the other position it connects the original one to the board. This will be a bit slower than the first method.

The best possibility is to use a variable capacitor with a range from about 18 (not lower) to 50pf. With a variable capacitor you would be able to adjust the speed continuously.

How to desolder C10:

You must have some experience in soldering, to do this! This is the way how I do it: Take a small screwdriver (like the one to open the calculator). Heat up one side of C10 (not longer than one second), quickly change to the other side and heat it up, change back and so on while you are carefully trying to push away C10 with the screwdriver. DON'T push too hard and DON'T heat up C10 too long!
If you push too hard you might destroy the solder pads! However there is a way to connect the capacitor even if the pads are destroyed but it's much more difficult.

How to solder the 20pF capacitor to the board:

The original capacitor is a SMD (surface mounted device) they are rather small and more difficult to get, but you can use any 20pF ceramic capacitor, which is small enough to fit in. If you get a regular ceramic capacitor it should look like the picture below (not that big, it should be about 1/6 x 1/6 inch large).
Note: It is possible that your capacitor looks different, the most important thing is that it is labled 20pF!

capacitor

To solder it directly to the board, proceed like this (see ASCII pictures below): Cut the two wires from the capacitor after about 1/4 of an inch and bend them about 1/8 of an inch away from the capacitor (but be careful not to damage the capacitor). Now you can solder the two ends to the board.

(top view)
 
     +---+
0----|   |
     |   |
0----|   |
     +---+
 
(side view)
 
    +---+
+---|   |
|   +---+
|
 

Using a variable capacitor:

The best possibility to adjust the speed of the TI-89 is to use a variable capacitor with a range of about 18 (not lower!) to 50pf. With a variable capacitor you would be able to adjust the speed continuously.
To do this you need two about one inch long wires, the variable capacitor and an electric drill. First solder one end of each wire to one pad where C10 used to be (after removing C10, you won't need C10 anymore) it really doesn't matter which terminals you use.
Now solder the variable capacitor to the other end of the wires. If the variable capacitor has three connections, connection one and two are connected together. Solder one wire to connection one or two and the other to connection three. If your capacitor has just two connections it doesn't matter which terminals you use.
Make sure that all your wires are as short as possible otherwise your calculator won't be as fast as it could be. I found it easiest to run the wires around U5 and then tape them down using lack electrical tape. Just use small pieces of tape. Try not to cover any components on the board. Especially not the connections of the backup battery!
Take off the back of the TI and remove all batteries, make a hole next to the backup battery like on the picture below, just large enough to hold the variable capacitor.

mounted variable capacitor

Place the variable capacitor in the hole and make sure that you are still able to close the battery cover, maybe you have to shave it a bit or make a hole in the cover too. I used a hot glue gun to secure the variable capacitor, but just about any type of glue should work. Put the glue only to the bottom of the variable capacitor on the inner side of the case. Make sure that you don't put any glue at the top of the variable capacitor so that you're still able to adjust it.
The last thing I did was to put black tape on the silver shield where the variable capacitor would touch when the case is put back together (don't cover any parts of the board especially not the parts where the connectors of the backup battery touch it). 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 variable capacitor.
The variable capacitor can be adjusted with a small screwdriver. (the capacitance is adjusted continuously by moving the plates of the capacitor) You have to try out which position is the fast and which is slow. In general you can adjust the speed from 80% to 200% of the original speed.

 

Important:

Note: When your calculator turns on with a few rows of black lines after you have accelerated it, you have to completely reset the calculator. Click here to see how

If you have any questions please first have a look at the SpeedUp FAQs and Trouble shooting if your question(s) are not answered there, feel free to send me an e-mail

Boris Lutz
blutz@stud.ee.ethz.ch
http://www.stud.ee.ethz.ch/~blutz/

You can share this plan with other TI users as long as you don't change it and include my e-mail address and home page URL.



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