Troubleshooting guide

Cinematronics Vector Monitor Repair Guide v.1.0
Page 5 of 53
DEFLECTION AMPLIFIER CIRCUIT
The deflection amplifier circuit can be further divided into two identical channels: one for the
horizontal deflection (“X”) and one for the vertical deflection (“Y”). Because both channels are
identical, we will only discuss the horizontal channel in this document.
The deflection circuit receives digital numbers from the logic board that represent the coordinates
for the beginning and end points of each line segment. The deflection circuit output is a current sent
to the yoke windings that is proportional to these numbers. So, the purpose of the deflection
circuitry is to convert a binary coded number into a current. This conversion is accomplished with
the following components.
DAC – Digital to Analog Converter
The first step in creating an image on the screen is to convert the digital coordinate numbers into an
analog voltage. The DAC-80 is the device that does this.
Digital information from the Cinematronics CPU (the “CCPU”), in the form of a twelve-bit word,
is applied to the input of the DAC-80 digital to analog converter (IC101) on pins one through
twelve. The most significant bit is applied to pin one, and the least significant bit is applied to pin
twelve. The DAC-80 makes the necessary conversion from digital signals to analog signals, which
are outputted as analog voltage signals on pin fifteen (proportional in level depending on the input
word applied). The result is a positive and negative voltage signal about its reference voltage.
Remember, there is no "sync" signal present, and the signal is not true video as seen in raster scan
monitors.
Pins one through twelve of the DAC can represent any number between –2,048 and +2,047. The
output voltage range is from –5 volts to +5 volts. When the DAC is operating properly, the output
signal is centered about 0 volts and bounded between +/-5 volts.
DAC CIRCUIT