© by: Boris Lutz
I replaced the capacitor C11 (47pF)
which is responsible for the speed with a smaller one (8pF).
This makes the TI about
The
accelerated version of the TI-92 needs only about 2 times the power
of a regular TI-92.
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, my
TI-92 II is running for several months without any problems and the
accelerated TI-85 works fine too, and this since 1992!
Don't use a capacitor with a capacitance below 8pF, 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 2 times the power of a regular TI-92)
The procedure described on this page is for the TI-92, the procedure
for the TI-81, TI-82, TI-83, TI-85, TI-86 and TI-89 you can find
here.
First make a backup then open the back of the TI-92 just as if you would change the batteries. Now remove all batteries and the 13 screws and the memory unit (the black box next to the backup battery, in the lower left corner). Put the memory unit in a safe place. You can remove the black plastic cover now.
+--------------------------------------------------+ | +----+ +----+ | | | | | | | | | | | | | | | | | | | | | B | | B | | | | a | | a | | | | t | | t | | | | t | | t | | | | e | BackUp bat | e | | | | r | | r | | | | i | +-----------+ | i | | | | e | | | | e | | | | s | | MemUnit | | s | | | | | | | | | | | | | | | | | | | +----+ +-----------+ +----+ | +--------------------------------------------------+
If your TI-92 has a silver shield covering the TI's circuit board,
you have to remove it first. Now you can see the board, at the bottom
you see the connectors of the memory unit, above it is U1 and on the
right side of U1 is the CPU.
The first picture is of a TI-92 the second is of a TI-92 II some
versions of the TI-92 might have a slightly different layout, however
the capacitor you have to replace is always labled C11.
This plan shows an enlargement +-----------------+ C31
of the part of the TI-92 board | | XXX
around C11. | |
It shows the precise location | | R C
of C11: | MC | 1 1
| | 9 1
If you want to have a closer look | |
at the location of C11 click here | | XXX XXX
| |
+-----------------+ C C
1 4
3 6
This plan shows an enlargement C1
of the part of the TI-92 II board C46
around C11. C R C12
It shows the precise location 1 R 2
of C11: 1 1 3
9
If you want to have a closer look +-----------------+
at the location of C11 click here | |
| |
| |
| |
| MC |
| |
| |
| |
| |
+-----------------+
First desolder C11 from the board. Be careful: Do not
overheat any part!! Now you put the
8pF capacitor where the old C11 used
to be.
Some TIs might work with a capacitor below 8pF, however this won't
work on all TI-92s and is surely not as stable as a 8pF (I tested the
8pF cap with several models and all worked fine).
That's it, put back the shield (be sure, that it's position is
properly adjusted), fasten the black the plastic cover with the
screws, put back the memory unit and the batteries.
Just removing C11, 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-92 to freeze. (you have to reset it).
Implementing a switch is possible. To do
this, you have to use a 10pF capacitor connected in series with the
original capacitor and the switch over the 10pF capacitor (when the
switch is closed the 10pF capacitor is short circuited). Note: if you
want to implement a switch you will have to use a 10pF capacitor not
a 8pF!
When the switch is closed the 10pF capacitor is bypassed and you have
the original capacity. If the switch is open you have a capacity of
1/(1/10 + 1/47) = 8pF
The easiest way is to just replace the original 47pF capacitor with a 8pF (or larger) capacitor.
The best possibility is to use a variable capacitor with a range from about 6 (not lower) to 50pf. 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 C11 (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 C11 with the screwdriver. DON'T push too hard
and DON'T heat up C11 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.
The original capacitor is a SMD (surface mounted device) they are
rather small and more difficult to get, but you can use any 8pF
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 8pF!
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)
+---+
+---| |
| +---+
|
Resolder the bottom side of C11 to the top pad (where C11 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 10pF cap to both terminals on the
switch where the wires touch.
Solder one of the wires to the top of C11 (the part of C11 that
hasn't been soldered to the board). Solder the other wire to the pad
where the bottom of C11 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-- | \ | | \ 10pF 0 \ | 0-- <--- Location, where the old C11 used to be | ===--C11--0
When the switch is closed the 10pF 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/ ( (1/10) + (1/47) ) = 8.25pf (which is approximately 8pf)
Now, the electrical stuff is done. Take off the back of the TI and
remove all batteries, make a square hole just above where C11 used to
be, but make sure that it doesn't touch the CPU when the case is put
back together again. Make the hole just large enough to hold the
switch.
Place the switch in the hole. I used a hot glue gun to secure the
switch, but just about any type of glue should work. Put the glue
only to the bottom of the switch on the inner side of the case. Make
sure that you don't put any glue at the top of the switch.
The last thing I did was to put black tape on the back of the switch
where it would touch when the case is put back together. If your
TI-92 has a silver shield you have to cut a small square notch out of
the shield for the two wires to bend up from the board to the switch.
The best possibility to adjust the speed of the TI-92 is to use a
variable capacitor with a range of
about 6 (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 C11 used to be (after removing C11, you won't need C11
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.
Take off the back of the TI and remove all batteries, make a hole
just above where C11 used to be, but make sure that it doesn't touch
the CPU when the case is put back together again. Make the hole just
large enough to hold the variable capacitor.
Place the variable capacitor in the hole, maybe you want to make a
hole in the back cover too, to be able to adjust the speed with the
back cover closed. 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 back of the
variable capacitor where it would touch when the case is put back
together. If your TI-92 has a silver shield you have to cut a small
square notch out 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 250% 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.