Commodore sx-64 keyboard cleaning

Louis Florit florit at
Wed Jul 13 14:17:53 CDT 2005

Hi, continuing the saga of the no worky sx-64 keyboard, I found these
instructions.  I will be reseating the chips in the sx-64 and
following these steps- hopefully the bladder won't be ruined in the



     This keyboard is completely different than previous CBM designs. 
Therefore, some of the previous information in this article will not 
apply. You need to know how this one works to be able to safely take it
apart for cleaning. The main component is a conductive rubber bladder 
separated from the PC board underneath by a white or grey plastic sheet 
with holes in it. The plastic sheet is an insulator. Until a key is 
pressed, the insulator holds the bladder away from the PC board contact 
points. If the insulator gets damaged or distorted, some keys will not 
work or may make contact all the time. Removing the bladder from the PC 
board requires great care. The insulator tends to stick to the board 
near each contact point. If pulled away quickly, it will most certainly 
be torn. I use a dental pick to slowly nudge the tiny areas that stick 
as I gently pull the bladder off the board. The last one took me about 
10 minutes to remove. That work cannot be rushed. Some areas of the 
elastic insulator deform as they pull loose and must be pushed back into 
place before reassembly. 
     The keyboard comes apart for cleaning by pressing in on the four
plastic snaps on the front edge while separating front and rear panels
with fingers. The two center ones are easy... just press in and up on
the brown plastic top panel and it will bend upward. The two side snaps
need a bit of pressure... use a small flat tool like a screwdriver
blade inserted into the slots to make them release. With the top off,
the keyboard is visible as several rows of keys over a conductive
rubber bladder, which in turn is mounted over a PC board. Each key
plunger assembly can be removed for cleaning if one or more are sticky
from a spill. They would -all- have to be removed to gain access to the
PC board under the bladder. None of the keyboard parts are 
interchangeable with a C64. Note that the shift-lock key is not a 
latching switch as in a C64 or C128, but a momentary contact
pushbutton like all the rest. A circuit in the SX forms the "latching"
device and an LED on the keyboard key comes on when ShiftLock is on. 

     The following is a report from a fellow user who sucessfully cleaned 
his SX keyboard:
"I am pleased to report complete success with my efforts to clean the key
pads on my SX64 and the keyboard is working like new again. Although not a
terribly difficult operation, care must be taken.
After removing the upper keyboard case half I removed the five screws along
the front of the circuit board that holds it in place. I then removed the
two screws holding the keyboard cable connector in place. At this point I
removed the keyboard from the lower case half and removed the keys one at a
time by pressing the two tabs together from the back side of the circuit
board that hold the key assembly in place. I didn't bother to keep the keys
in order as I would use a C64 keyboard as a guide when replacing the keys.
I then removed the two tiny screws that hold a small strip of metal to the
black rubber like bladder on the right side. At this point I was ready to
lift the bladder from the circuit board. Under the bladder is a grayish
colored membrane that is somewhat fragile and care must be taken not to tear
it. On several occasions this membrane stuck to the circuit board as I
attempted to lift the membrane from the circuit board. I used the tip of a
very small thin flat screwdriver to ease the membrane off the circuit board
when it would stick.
     Once the membrane was removed I cleaned all contact pads on the 
circuit board using cotton swabs (Q-tips) and alcohol. I also cleaned the 
contact areas on the bladder in the same manner using VERY LIGHT pressure. 
I replaced the membrane onto the board and attached the metal strip with
it's two tiny screws. I attached the cable connector and mounted the board
in the lower case half with the five screws. Take care not to over tighten
the screw that goes through the bladder to avoid damage. After the board was
secure in the case half, I replaced the keys. They simply press into place.
The space bar will require a little care to line up all three connectors.
Replace the upper case half and that's it. Not that difficult but very time
consuming and it does not pay to hurry. While the key assemblies are off the
keyboard it is a good time to clean the keys themselves and to blow any dust
or debris from the underside of the key. If you find this information useful 
please feel free to pass it along to others."  Charles Houck

     All I have to add to what Charles has said is some cautions when
cleaning the contact points. Never use anything abrasive on the bladder.
The black dots are the contacts. They are just a conductive coating on 
plastic, so rough treatment can easily destroy the bladder beyond repair. 
A -light- rub with a dry Q-tip is all that is needed on each black spot.
For the copper keyboard contacts, I use a #2 pencil eraser to remove 
oxidation from each contact point, then rub each with a dry Q-tip to 
"polish" the surface. The resulting contacts should be shiny with no 
spots or blemishes. I don't use solvents unless the board and/or bladder 
is contaminated because of a liquid spill. 

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