Troubleshooting guide
Cinematronics Vector Monitor Repair Guide v.1.0
Page 41 of 53
pulses dropping down to a 40-volt level. If no pulses, probe IC7 pin 4 with a scope and observe
data pulses. If the pulses are present on IC7, check Q2 & Q3 with an ohmmeter or transistor
checker.
• Check the cathode of diode D5 for a full wave rectified, unfiltered voltage signal floating at
+25 volts.
• Check seating of CRT plug. Remove and probe with scope to verify presence of proper signals.
• Check the neck of the CRT for a glowing filament. If there is no glow, check the brown &
black twisted pair of the CRT plug for 6.3 volts AC.
• Be sure all connections to the CPU board and monitor are firmly seated.
Symptom: High Voltage Too High/Too Low.
An accurate High Voltage meter will read 16KV to 18KV if high voltage is good (depending on
which version of the monitor you have). Self-contained HV meters vary widely in accuracy. If +90
and +400 volts out of the high voltage supply are good, chances are 16KV/18KV is good. If +90 or
+400 volts are bad, repair or replace high voltage supply.
Symptom Summary: Discrete HV monitor stays up for about 10 seconds, with deflection
chatter, no picture. Then the -25V breaker pops (then shortly after, the +25V breaker).
Measuring voltages, all regulators are outputting the correct voltages (+/-18VDC, +/-15VDC).
However, the +25VDC seems high (about 28 volts). The -25VDC is right on the money. However,
when the -25 pops, the +25VDC line dips down to +25VDC.
Unplugging the yoke and retrying, the breakers do not pop, and I get a nice white dot in the center
of the screen. I've checked the tantalum capacitors, diodes and transistors; they all seem fine.
With the yoke disconnected and neck harness disconnected, I decided to take a voltage reading
across the yoke inputs. As was Zonn's suspicions, one of the yokes was pegged to the -25VDC side.
So I had it narrowed down to an axis.
Then I tried the trick with swapping the wires that led from the DAC/Switch/OP amp section to the
deflection section. Unsoldering and resoldering new jumper wires from near the pots location to the
deflection side, I verified that the same problem exists, and that the working side was still good. So
I had narrowed it down to one axis deflection side.
First I thought something might be breaking down and connecting the -25VDC directly to the yoke
output, so I shotgun replaced all the diodes in that section. No change.