Issue: The sixth row of switches on DM was not registering at all. A fault on the CPU was suspected, as it was recently cleaned of battery leakage damage.

Solution: Responsible for row 6 is the white-blue wire, as per ops manual -


Looking at the schematics for the wpc-89 cpu board, we see the following components involved coming from J209-7 -


We can see J209-7 to D8, cont to R61/R62, to a LM339 at pos U19 pins 8,9 with an output at pin 14, cont to LS240 at U13 pin 4 and R32.

Using an DMM, checking for continuity as by the abovementioned path revealed a bad trace between U19 pin 14 to R32 and U13 pin 4. Soldered a wire jumper from U19 pin4 to R32, switches are now registering. Issue resolved.