Troubleshooting guide

Cinematronics Vector Monitor Repair Guide v.1.0
Page 33 of 53
Test Procedures
Deflection Circuit Test Procedure. To test each DAC-80, you must first verify proper power on
pins 13, 14 and 22. Remove the LF13331 analog switch at IC1. A DC meter should read
approximately 0 volts at pin 15 of the DAC. Check pins 1 through 12 with a logic probe, most of
the lines should be pulsing.
Analog Switch Test Procedure. The LF13331 at IC1 should produce a charging waveform
centered about 0 volts on the switch output pins. The upper channel waveform should be of greater
peak-to-peak magnitude than the lower channel. You will need an oscilloscope to see these
waveforms. If in doubt, replace the switch.
R/C Network Test Procedure. If the line segments on the monitor are adjustable but bowed,
replace C101. If the line segments cannot be adjusted to intersect, verify proper resistance of R103
and R102 as R102 is rotated.
Edge Gain Amplifier Test Procedure. Observe the input signal on pin 3 of IC102 or IC202. The
waveform at pin 6 should be the same with an average gain of 2. The signal should be centered and
bounded between +/- 2 volts. If these signals are correct, check diodes D201-D204.
Deflection Amplifier Test Procedure. If the game is blowing circuit breakers the problem is
almost always a transistor in the deflection section. Recommended test procedure is to check each
transistor in circuit with a transistor checker. Lift diodes D112 and D113 to check transistors Q106
and Q107. In the horizontal section, lift diodes D212 and D213 to check Q206 and Q207.
Check the 4 transistors on the heatsink with an ohmmeter. I found it easer to remove the heatsinks
one at a time to gain access to the pins of the transistors but I guess you can test at the connector if
you know which wire goes to which pin. If you can hear deflection noises when your monitor is
powered up, your output transistors are probably working. Be careful though, you can still hear the
noise even if one channel is dead.
If a scope is available, the defective channel can easily be located. Step 1: Remove the deflection
yoke connector (J5) from the display board. Step 2: Reset the breakers and power up the game.
With the scope, probe the cases of transistors Q104 and Q204. There should be pulses clipped at
+25 volts and –25 volts. The defective channel will not have these pulses. Once the defective
channel is located, start at the appropriate DAC and proceed forward through the circuit until you
find the bad component(s).
Replace the LF13331 analog switch at IC1. This is the quickest manner to verify proper operation
of the deflection circuit.