Philips PM3094 Z mode input

[WaveyDipole]

I recently acquired a HP3314A signal generator and was experimenting with the sweep mode but couldn't get the marker to work. I checked the output from the Z out on the HP3314 on the oscilloscope and could clearly see a trace showing the positive blanking signal (+18vp approx) and a marker pulse (-18vp approx). I then did a test on the Z-MOD input of the PM3094 and found that aplying a positive voltage blanked the screen as expected, but applying a negative voltage did not brighten the screen. As a final test I tried the sweep generator and marker on a Tek 465 and here, accuracy aside, it worked as expected, generating a clear highlighted marker.

I can just use a start and stop frequency that provides an appropriate calculable frequency per div and even add a cursor, but was wondering whether this an expected behaviour, or a fault? Has anyone used the Z-MOD input on a Philips PM3084 or PM3094 and did it work?