Inability to adjust frequency display enough on a Tektronix 492 spectrum analyzer


Good afternon, all,

I have a question about a Tektronix 492 spectrum analyzer that I just purchased. Basically what I'm seeing is that when I run through the calibration sequence on pages 3-8 and 3-9 of the manual, I cannot find any way to adjust the displayed frequency of the calibration marker signal to anything higher than 78 MHz. When I center the 100 MHz signal from either the internal generator or an external source and then hit "Cal", I can only adjust up so far (78 or 79 MHz) and then the adjustment is maxed out. I've futzed with this for hours and can't seem to make any headway.

Also, probably related, when I view a broader chunk of spectrum on, say, 100 MHz per division I see that each of the subsequent harmonics each fall just a bit more short of the next 100 MHz vertical graticule: so the 200 MHz harmonic is displayed a little left of the next vertical graticule, the 300 MHz harmonic is a bit more to the left of what should be the 300 MHz graticule, 400 MHz a little further left, and so on.

If you have some idea of what I might try, I'd sure appreciate your insight.

Thanks and all the best,