Troubleshooting guide

Cinematronics Vector Monitor Repair Guide v.1.0
Page 36 of 53
If you have a bad ROM image, the breakers will almost always pop. Is this bad for the game? YES!
The breakers pop because the beam was deflected clear off the screen. This is VERY hard on
output transistors in the deflection circuits.
Lets say you have a monitor popping breakers. Some would suggest that you disconnect the power
transistor and see if everything runs ok without them. But what are the possible problems for
blowing a breaker?
1) Bad power transistors.
2) Bad LF13331
3) Bad DAC80
4) Bad CPU board drivers
5) Bad voltage regulator
6) Bad built in HV unit
There are assuredly more things than that which may cause a breaker to pop, but these are the main
reasons. If 2, 3, or 4 and possibly 5 were the problem, the CRT trace is going to be sent to the
extreme edges of the screen, and that's going to burn up a pre-driver transistor/resistor. If you keep
running your monitor with the power transistors disconnected, you are now going to have two
problems, the original and the one just created by removing the power transistors and running the
monitor.
At this point you might ask “has anyone ever set up inline fuses to the deflection transistors to
protect the display board components should the deflection transistors go?”
Careful there. Anything that partially disconnects the output transistors from the drivers will cause
driver damage (like unplugging the output transistors). If you add fuses they should be in series
with the yoke, but I’m not too certain what benefit – if any – can be achieved by fusing the yoke.
You can try running the monitor without the Yoke plugged in, this is ok. But DO NOT run it with
the yoke plugged in and without the power transistors plugged in! The outputs are darlingtons and
if you unplug the output transistors, the pre-drivers will try to drive the whole monitor, and they
just can't do it! If you had an output blow, you might want to test these pre-drivers as well. (Q108,
Q109, Q208 and Q209).
If the circuit breakers quit blowing when you unplug the yoke, you may want to put a scope on the
outputs of IC102 and IC202. If the output just sits at some negative voltage (like -5V) then
something is wrong. If one of the transistors is blown, you might be driving an output maximally
negative. If this is the case, trace back through the OP amps and analog switch and find the bad
part. If you suspect a bad DAC, try swapping them. If the trouble moves it's a DAC, if not it could
be the CPU itself.
You can unplug the deflection coil and put a multimeter across the X or Y coil outputs and see
what kind of voltages are being sent to the coil, which helps greatly in debugging. You can also