Troubleshooting guide

Cinematronics Vector Monitor Repair Guide v.1.0
Page 35 of 53
SYMPTOM DIAGNOSIS
The following symptoms and diagnosis come from various people and sources.
I cannot verify any of these will work for you.
Symptom: Monitor trips breaker.
• Check transistor Q211 (2N5876)
• Check diodes D107-D111 if there is a loss of Y (or X) deflection just before breaker trips.
Here is a systematic guide to trouble shooting a monitor that blows breakers. Monitor must be
connected to a good CPU. Check for burned components. The first thing we want to do is be able
to power up the monitor without blowing breakers - then do the troubleshooting.
1. POWER OFF. Unplug yoke from monitor board. Unplug socket from CRT.
2. POWER ON.
If breakers blow: POWER OFF. See A.
If breakers hold: Check outputs of -15v, +15v, and +5v regulators. Output must be within
+/-0.5 volt tolerance.
A. POWER OFF. Unplug heat sink wiring harnesses from monitor board. POWER ON.
Breakers blow: POWER OFF See B. Breakers hold: one or more of Q110, Q111, Q210,
Q211 are shorted. Damage elsewhere is likely. Follow procedure at 3.
B. Problem is most likely Video High Voltage module. Unplug from board and POWER
ON. Breakers hold: replace or repair Video power supply. Breakers blow: Maybe a
shorted tantalum capacitor.
3. Use an oscilloscope to check deflection circuits for proper signal. 1mv/div time base is a
good scope setting. Between the DAC-80 output and input of Q101 or Q201, the signal
amplitude is about +/-3 volts peak. The DC component should be less than +/-200mv. Too
much DC component will trip the breakers. If the signal into Q101/Q201 is good, problem
is most likely in the deflection amps. With the yoke disconnected, a good deflection
amplifier will put out an odd looking “square wave”, swinging between +25 volts. To check
a bad deflection amp, check all transistors. Look for burned resistors at R118, R119, R113,
R117, or R218, R219, R213, R217. Resistors R115, R116, R120, R121 may open with no
burn marks. For test purposes, protection transistors Q106, Q107, Q206, Q207 may be
removed from the circuit and amplifier can be powered up. Always replace protection
transistors before returning monitor to normal service.