Hi Jim

First,verify your power suplies meet voltage,noise and ripple specs.

IIRC,there was a pot somewhere to adjust RO wiggle.
the CAL procedure ought to mention it,or the circuit description.

Thanks for the suggestions; I'm flicking through the service manual at
the moment. It's a 'scope I won at auction and am hoping to sort out.
I'll let you know what I find!

Thanks
Jon N