Texas Instruments TI-89 Tip List page 29

dishwasher for about ten minutes. Remove the key caps as needed, and wash and rinse them.
Wash the circular gold patterns on the display side of the PCB, but try to keep the water away
from the display. Wash the rubber keypad sheet; the black bumps make the switch contacts
and need to be cleaned well. You may need to pull back the foil shield sheet to thoroughly
clean the printed circuit boards (PCBs).
4. Gently dry the washed components with a hair dryer. Avoid over-heating the printed circuit
board and plastic parts. The goal of this step is to quickly evaporate the water without
damaging the parts from excessive heat.
5. Let the calculator dry for at least 24 hours.
6. Reassemble the calculator. See instructions below.
The instructions below apply to a HW1 TI-89 and a HW2 TI-92+. They may not apply to other hardware
versions.
Disassembly and assembly instructions for the TI-89
You will need a small Phillips screwdriver (#0), a Torx T6 driver, and a small flat-blade screwdriver to
pry out back-up battery.
Disassembly:
1. Place the calculator face down on a towel or other soft surface.
2. Remove the battery access cover and the four AAA cells.
3. Remove Phillips screw over back-up battery door, then remove the door. Remove the back-up
battery. The battery is spring-loaded, so place your finger over the battery as you pry it out, or
it may go zinging up in the air, like mine did.
4. Remove the six T-6 Torx fasteners around the outer edge of back of calculator.
5. Remove the back plastic cover: squeeze the edges in at the top of the calculator and pull back
until this end pops out. Then gently wiggle it back and forth while pulling back, and the back
will pop off fairly easily.
6. Remove the two phillips-head screws holding shield foil.
7. Hold the shield foil back and remove the four phillips-head head screws, under foil. These four
screws hold the printed circuit board (PCB) in.
8. Gently remove the PCB. The key caps are loose, so keep the front of the calculator facing
down, or they will fall out. Remove any key caps which are stuck to the rubber key sheet, and
replace them in the calculator front piece.
Assembly:
1. Install the rubber keypad sheet. Note that the rubber sheet only installs one way. Press all the
key 'bumps' into the key caps.
2. Install the PCB in the front cover. Ensure that the black plastic flap at the upper right of the
PCB is tucked inside case. Make sure all key caps are still in place.
3. Install the two phillips-head screws through foil shield.
4. Install the four phillips-head screws that hold the PCB.
5. Install the plastic back piece. Align the front and back piece and press them together until they
snap closed.
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