@Bruce
It's so frustrating only having a short time every day to look into this problem. I only get enough time to perform a one or two quick checks each time at best. Now it's very late here again and I can do no more today. I'm really liking your suggestion of inserting a clean external 10Mhz signal from a separate source, though! I'll definitely give that a try as it could possibly identify a faulty reference oscillator as the culprit very quickly.
But that's for the weekend....
@Matt
I'm not sure what you mean. My analyser seems to only have one 10Mhz output: a BNC socket on the rear panel. The schematic doesn't show any other one, either. Looks like the ref osc is a module that can't be internally tested, which is a damn nuisance. If I can't get at it to repair it then I'm stuck with these greedy fellows on Ebay who charge a mint for these things, which they've ripped out of 'for spares or not working' units for peanuts. Sigh....
Jinxie