Yeah, looks like your signal is going south on you. I would start and make sure the signal is good coming from the pcb (make sure the pcb is good) next check the signal getting to the monitor (the ribbon cables are notorious for going bad) check the DAC's - swap them and see if the signal changes from Vert to horz issues (bad DAC) or swap with two known good DACS - the DAC sockets may be questionable also. and finally if the signal is good at that point Check the LF13331N (NTE861) analog switch and the TL081 op amps. Also check the solders on the adjustment pots, they can send a funky signal too.
check
pcb
ribbon cable
DAC and or sockets
analog switch
hope that helps, if you anything pm me.
Mark