[PETERg0rsq]

Just a further thought on what you saud

The 3.9kHz oscillation is probably correct, and by removing it with a capacitor to ground has disabled the function of the ROM!

The pulses enter Q11 on pin 1 and are used to pulse the outputs to the level shifters.

This pulsing is needed to generate tunning pulses on the Step up or step down lines, which are sent to the digital board to simulate tunning pulses to steer the counter in the correct direction to bring the divider to the correct value to bring the output back into the band.

Have you checked what is happening on STEP UP and STEP DOWN lines. If the N counter is too high then you should get pulses on the step down line, and if the n-Counter is too low you should get pulses on the step up line.

One of the first diagnostic steps I take with the 9081 and tunning issues is to disconnect these lines and see what the frequency coverage of the generator is, as if one of the N-Counters fails, or one of the N dividers fail, then the PROM detects an out of band signal and tries to tune back into band constantly.

This sounds like what you are experiencing when not able to tune down below 492 MHZ