Hello Dave,
I would try to allign all the 3 filters in the VR unit (Variable Resolution Module). After so many years the trimmer contact (internal) might have worsen a bit and one or more filters might not have the right shape or the amplitude might be too low. So it perhaps helps to exercise these trimmers one by one while looking at the filter shape using the calibrator signal. Please take note that the calibrator signal can be not exactly 100MHz. In the VR unit there are the 300kHz, 30kHz and the 3kHz filters. Unscrew the VR unit and try to flip it so the bottom side comes into view. Have a look at the Service Manual about this too.
The 300 Hz filter is on a smaller seperate board. The trimmers for this one are hard to reach. You need an extension board for this one. I would skip this one for the time being.
Hope to hear from you.
Jaap PA0JRK
