Will Louis wrote in news: snipped-for-privacy@4ax.com:
There is no internal trimmer pot for this.You may be thinking of the R-O jitter pot.
You probably have a bad sample/hold cap(0.1uf DIP or glass cap) on one of the op-amps that digitize the front panel pots(on the microprocessor PCB.).
You need to READ the CIRCUIT DESCRIPTION in order to understand how this scope works.It's well worth it. There also are exercizer routines accessed thru diagnostic menus that let you check out the front panel pots range.