Troubleshooting guide

Cinematronics Vector Monitor Repair Guide v.1.0
Page 34 of 53
Intensity Circuit Test Procedures. To isolate a no display condition to the intensity circuit, probe
the yellow cathode wire at the CRT plug, turn the brightness full clockwise and observe a +90 volt
base with pulses at +40 volts. If pulses are missing, jumper Q2 collector to emitter. If the picture
returns, check F1 in the power supply and replace Q2 (2N3904).
Observe +2.75 volt pulses at pin 4 of IC7. If the pulses or voltage is missing, verify pulses at input
pin 3 of IC7. Check for +5 volts at the junction of R1 and R2. Replace IC7. If you observe pulses at
+4 volts, replace Q2. The output of pin 4 will exceed 2.75 volts if there is no load due to a failed
transistor.
High Voltage Oscillator Test Procedures – discrete HV monitor only. The vast majority of HV
failures will be the TIP41C (Q4). When this component fails, it will cause the +18 volt regulator to
shut down internally due to a now excessive load request, such as if Q4 were to have shorted.
Remove pin 3 of the transformer windings. With the load removed, the +18 volt regulator should
read +18 volts. The -18 volt regulator will read -18 or -25 volts. Replace Q4, C17, D7 and the
defective regulator all at once.
D10 and D6 are high voltage, fast recovery diodes that will not read with an ordinary meter. To
test, lift the cathode from the circuit and observe rectifying properties.