Troubleshooting guide

Cinematronics Vector Monitor Repair Guide v.1.0
Page 39 of 53
Symptom: Picture on the right side of the screen only. Game plays, but some of the vectors
are a little ‘off’. Vectors seem correct horizontally but zigzag vertically downwards from the
drawn object.
This can be caused by a few things: bad connections between the monitor and the ribbon cable that
runs between the game board and the monitor, bad transistors in the deflection circuit. Try wiggling
the ribbon cable at both the CCPU end and the monitor end. Since there are misdrawn vectors,
perhaps there is a bad DAC or a bad LF13331 analog switch. This problem can best be checked
with a scope.
Using your scope, check the DAC output at the TL081s. If you see a perfect copy of the game in
XY-mode (comparing outputs of TL081s), you know the DACs/analog switch and op amps are
working OK. Follow the signal through to the collector of Q104 (vertical) or Q204 (horizontal) and
keep the scope in XY mode. Once you find the same image that is being mis-drawn on your
monitor screen, you will have found the portion of the monitor that is not working correctly.
Also check all the resistors around where the deflection transistors plug into the board. They get
burned up frequently. Check the solder joints of the molexes that these transistors plug into;
plugging/unplugging of these connectors often weakens the joints.
Try switching the molexes of the heatsink-mounted transistors to see if the distortion changes
‘position’ on the screen. I would suggest trying this even if you know that both sets of transistors
are good.
Symptom: Picture on Display Jitters.
• Replace analog switch IC1.
• Check size pots R109 and R209 for wiper noise by turning briskly while observing the screen.
• Readjust for proper screen size.
• Check for bad solder connections on R109 & R209.
• Check DAC IC101 & IC201 for bad solder connections.
• Ensure that all molex connectors are properly seated.
Symptom: Dotted Display.
• Check IC7 pins 2 and 4.
• Verify proper operation of IC1.
• Check for proper +25 and -25 volts DC.
• Check operation of DAC’s IC101 and IC201.
• On CCPU logic board, check IC8 pin 2 for pulses.
• Verify signal presence at analog switch IC1.