Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, possibly a low or missing +5V supply to the non-functioning half (likely) and/or a failed limiting resistor (most likely). Of course, it can still be a wiring/connector issue (least likely).
If considering a DIY (do-it-yourself) repair approach, do you have access to and familiar with a multi-meter and even a soldering iron?
Great on the DIY John!
Please locate the Keyboard Interface Board / 760995. De-solder at least 1 leg of resistors R9 and R12. Test each resistance which should read 10KΩ.
Check and re-fit connector CN2. Might as well do CN4.
Inspect for cold-solder on all solder joints.
Agree on the PCB# *****
Propose next check would be on IC2.
Would the schematic diagram serve your purpose?
Hi again John.
Please click HERE.
The schematic diagram is in a Portable Document Format (PDF) file and can be viewed in most web browser. Click on the link to open the file or right click then select “Save As…” to download the file. It would require Adobe Acrobat Reader or equivalent for this purpose.
Hope that the above service information may serve your purpose and would appreciate a Positive Rating and/or an Accept if so warranted (if haven't done so).
Were you able to download the schematics?