Troubleshooting guide

Cinematronics Vector Monitor Repair Guide v.1.0
Page 11 of 53
HIGH VOLTAGE SUPPLY
The high voltage and cathode circuitry is the second section of the Cinematronics monitor. This
section also contains the necessary voltage regulation to power the ICs located on the display
board.
For the early ‘discrete’ – style monitors, IC3 (7818) and IC5 (7918) provide positive 18V and
negative 18V used in the high voltage transformer (T-l) and oscillator (the oscillator circuit is
necessary because there is no horizontal sync used to develop the high voltage pulses). The
oscillator circuit is comprised of primary windings, Q4 and associated discrete components. For the
later ‘Keltron’ – style monitors, IC4 (7815) and IC6 (7915) provide positive 15V and negative 15V
respectively to power the DAC-80s and the TL081 op-amps on the display board.
The high voltage (18KV on discrete HVs and 16KV on non-discrete ‘Kelton’ HVs) is developed by
Transformer T1’s secondary windings, and the high voltage tripler in the discrete design. The
Keltron contains what is called the high voltage quadrupler – even though it produces less voltage
than the discrete version.
Intensity Circuit (‘Z’ Channel)
The beam can be turned on and off by applying the proper voltage level to the CRT cathode. Beam
cut off is +90 volts DC. At this potential, the electrons excited by the filament prefer to remain on
the cathode and none make it to the screen of the CRT. Lowering this potential allows more
electrons to escape to the anode. We can then produce a NORMAL INTENSITY level by lowering
the cathode potential to +40 volts DC, and a HIGH INTENSITY by lowering the potential to, say,
+20 volts DC.
The Cinematronics CPU produces two intensity levels by sending low pulses to pins 1 and 3 of IC7
(7406). Pin 1 is the HI INTENSITY channel and consists of IC7 and Q1. The NORMAL
INTENSITY channel consists of another part of IC7 and Q3. The CCPU also has a jumper setting
to produce variable intensities, but this option is only used on two games - Sundance (16 intensity
levels) and Solar Quest (64 intensity levels). These additional intensity levels are produced with
additional PCBs that are discussed in the following section.
The intensity and beam blanking control circuitry is composed of IC7, Q1, Q2, Q3, Q7 and Q8 and
associated components. A beam blanking voltage of +90 volts DC is generated from pin 8 of the
HV transformer secondary winding, D6 and C17. This half wave rectifier supplies the +90 volts to
one terminal of the brightness pot. The wiper of this pot picks off the proper voltage and sends it
through the yellow cathode wire to the CRT plug socket. R11 adjusts the amplitude of the negative
spikes used for brightness and intensification. A greater negative spike creates a brighter picture.
The cathode voltage rides at +90V, and the beam is turned “on” by negative voltage. Using an
oscilloscope, negative pulses can be seen at the anode of D4. These are the beam “on” pulses. For
normal intensity the pulses will go down to approximately +40V, for double intensity, +20V. Pins 3
and 4 of IC7 are the normal intensity control gate which receives information from the CCPU. Pin
1 and 2 of IC7 are the double intensity control gate. When a Hi going Lo signal is on pin 3 of IC7,
pin 4 will be a Lo going Hi, turning on Q3 on the Hi transition. Q3 acts as a switch connecting the
series network of R11, R10 and R9 to ground creating a voltage divider network. R11 is the manual
intensity control. When pin 2 of IC7 goes Hi, Q1 turns on for the duration of the pulse connecting