VT101 8085 CPU Fault

A little while back I posted about a possible 8085 CPU fault on my VT101 terminal controller. After a session with the logic analyser, courtesy of another member of this list, we determined that the 8085 was indeed bad. We substituted it with another 8085 and the terminal controller started working normally. However. This has revealed a fault on the monitor control board. There is the occasional vertical wobble. Sometimes the image is stable, then it will wobble up and down a bit, sometimes just a bit, sometimes more frequently, then it will stabilise for a few seconds, then it will wobble again, etc etc. I know it is the monitor control board because we sent the Video Out output to a separate monitor and it was perfect. I have checked the ESR on all the electrolytics, they are all fine. Prior to all this I had replaced C439 with a higher voltage rated component, as recommended here: https://trmm.net/VT100. I used a 100uF part, rated at 100V. I had also replaced C437 as that had a high ESR prior to seeing this problem. Is there anything else I should check? Regards Rob