The 7854 I'm trying to resurrect has a problem where the readout starts to flicker a lot after it has been on for a short while.
If I them power off and power on I see all vertical mode lights on and CHOP and B lit in the horizontal mode lights. This I understand is a "Real time clock" failure.
So where do I find the darn RTC so I can try to fix it - a quick scan of the friendly service manual didn't lead me to it ...
If this is like some of the others, the CPU doesn't have an RTC module, too old for that. I'd look for the battery, but I suspect you may have a dallas RAM/ROM buried in there, some of them have/had RTC modules.