© by: Boris Lutz
I replaced the capacitor C7 (27pF)
which is responsible for the speed with a smaller one (15pF).
This makes the TI
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 15pF, this won't be
stable! If you are using an accelerated TI, replace the batteries
when the display contrast is at level 8 or higher! (the accelerated
version needs about 1.5 times the power of a regular TI-82)
The procedure described on this page is for the TI-82, the procedure
for the TI-81, TI-83, TI-85, TI-86, TI-89 and TI-92 you can find
here.
First make a backup then remove all batteries. There are three
screws which need to be removed. Two right below the battery cover
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
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Open here slide until here (on both sides)
After opening the TI, you'll see a silver shield covering the TI's circuit boards. Remove the two small screws at the bottom and the one at the top of the shield. Once the screws are out, you'll see two circuit boards: a large one (Main board) and a smaller one for the display (Display board), C7 is on the main board.
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This plan shows an enlargement | |
of the part of the main board | |
around C7. | |
It shows the precise location | U 1 |
of C7: | |
If you want to have a closer look | |
at the location of C11 click here +----------+
J2 +------------------------+
E-C R | |
4 | |
C7 | |
| U 4 |
R17 | |
| |
R5 | |
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First desolder C7 from the board. Be careful: Do not overheat any part!! Do not burn the cable that connects the display board to the main board! Now put the 15pF capacitor where the old C7 used to be.
Just removing C7, 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-82 to freeze. (you have to reset it)
Implementing a switch is possible. To do
this, you have to use a 33pF capacitor connected in series with the
original capacitor and the switch over the 33pF capacitor (when the
switch is closed the 33pF capacitor is short circuited). Note: if you
want to implement a switch you will have to use a 33pF capacitor not
a 15pF!
When the switch is closed the 33pF capacitor is bypassed and you have
the original capacity. If the switch is open you have a capacity of
1/(1/33 + 1/27) = 15pF
The easiest way is to just replace the original 27pF capacitor with a 15pF (or larger) capacitor.
The best possibility is to use a variable capacitor with a range from about 10 to 30pf. With a variable capacitor you would be able to adjust the speed continuously.
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 C7 (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 C7 with the screwdriver. DON'T push too hard and
DON'T heat up C7 too long! Do not burn the cable that connects the
display board to the main board!
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.
The original capacitor is a SMD (surface mounted device) they are
rather small and more difficult to get, but you can use any 15pF
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 15pF!
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)
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0----| |
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0----| |
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(side view)
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If the TI is working but you can see some black lines across
the screen or something like this, you have to use a higher
capacity, something between 18 and 22pF. If you use 22pF instead of
15pF the TI will "only" be about 1.5 times as fast as with the
original 27pF.
In fact most calculators require a 18pF or larger capacitor, however
it is worth first trying the 15pF since this way your calculator will
be faster.
Resolder the bottom side of C7 to the top pad (where C7 was
connected before) leaving the bottom pad open. Now, solder two about
1.5 inches long wires to your switch. It really doesn't matter which
terminals you use. Now, solder the 33pF cap to both terminals on the
switch where the wires touch.
Solder one of the wires to the top of C7 (the part of C7 that hasn't
been soldered to the board). Solder the other wire to the pad where
the bottom of C7 used to be. Tape the wires 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!
Make sure that all your wires are as short as possible otherwise your
calculator won't be as fast as it could be.
=========== | | 0-- | \ | | \ 33pF 0 \ | 0-- <--- Location, where the old C7 used to be | ====--C7--0
When the switch is closed the 33pF capacitor is bypassed (short circuited) and you have the standard speed again. If the switch is open both capacitors are connected in series and you have a capacity of 1/ ( (1/33) + (1/27) ) = 14.85pf (which is approximately 15pf)
Now, the electrical stuff is done. The only thing left is to mount
the switch: Take off the back of the TI and remove all batteries. 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.
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.
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This picture shows an implemented 4-switch DIP-switch (only one switch is used). The switch is located on the right side of the backup battery. It doesn't matter if you use a 4 DIP-switch or just one, as long as it is small enough to fit in. It just depends on what is easier to get. Many thanks to Johan Rudholm [chomma@cd.chalmers.se] who sent me this picture. |
The best possibility to adjust the speed of the TI-82 is to use a
variable capacitor with a range of
about 10 to 30pf. With a variable capacitor you would be able to
adjust the speed continuously.
To do this you need two about 1.5 inches long wires, the variable
capacitor and an electric drill. First solder one end of each wire to
one pad where C7 used to be (after removing C7, you won't need C7
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. 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.
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. 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 50% to 200% of the
original speed.
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
Boris Lutz
http://www.twistednet.ch/
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.
