I have an Icom IC-RP1220 set for 1285.500 with a -12.0 input.
It's been out service for a few years, but was acting up before it was
pulled out. Now that I have time to play with it, I've noticed its
drifted 'up' 6KHz both on RX and TX, yet no chenges were made to the CPU
settings.

I have the owner's manual, but no service manual.

Is there a common xtal controlled base clock shared between the TX and
RX circuits? If so, where would the trimmer adjustment be located?

Or, if this is a problem experienced by others, and the cause is
something else, some advice would be very much appreciated!

Thanks!

Pat, VE3PMK