Cleaning a PET 8032 Keyboard for Vintage Computer Festival East 10.0


This is one of the computers I intended to run VisiCalc on for VCFeX.  It is a CBM 8032 that I bought locally from a Commodore executive who had stored it in a closet since 1985.  I unboxed it last year only to do a quick inspection and power on test.  The keys fought me while typing a hello world basic program so I knew for a while the keyboard was going to needed attention.  Now that a real use was at hand, it was time to make that keyboard sing.

So reviewing the situation again I found few keys were intermittent and “W” was  totally dead.  Getting down to business I removed the keyboard and took it to the bench.  First job is to remove the keycaps.


I like to lay the key caps out in sequence and put all the parts in bowls.


A bunch of small screws hold the circuit board to the key assembly.
There is also a set of wires to the shift lock key that need to be  UN-soldered in order to free the board.  Here is the business side of the circuit board.


And close up.  The conductive rubber pads of the switch shafts bridge the interleaved fingers of the gold contact areas.


You want to do a good enough job at this so that you only have to tear them down once.  Its not as bad of a job as I thought it was though.  

The pads were in good shape, still soft, and measured about 50ohms across on “W” and other pads that I spot checked.  I concluded most of the contact problems were dust and debris.  So I cleaned the contacts and the pads with 99% Isopropyl alcohol.  I put the keyboard partially back together, well enough to test it, and the intermittencies were gone.  Sadly the “W” key was still not functional at all.  This was looking like a wiring problem.

I took a look at the 8032 keyboard matrix from to see what keys were on the same row of the matrix.  The chart there for the business keyboard says W is on row 4 line. However measuring from the side of the W contacts that should go to #4 edge contact showed that it was open (blue line), meter reading 0. Note my red meter lead goes to row #4 on the back side of the board, so I drew in the red line to illustrate that. See those wide traces on the board? They are jumpers that connect different sections of the layout to other sections.  I suspect that the hockey stick shaped one under my blue line was the culprit of this disconnect.   My solution was to run a jumper from a safe convenient spot of the W key’s #4 connection and the #4 row pad on the edge connector following the line of this color below.


The green wire below is the patch wire for the W’s line to row #4 edge connector pad.  It was run underneath to avoid conflicts with key travel.


With that patch wire done, the keyboard worked great. It took about 2 hours to complete.

I may revisit this to do a less obtrusive repair.  It was recommended to me to use very thin transformer wire to path the open from the other side.


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Filed under PET, Vintage Bitage

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