Circuit Descriptions
1502C MTDR Service Manual
5–25
the output step height. It is referenced to the +5 V supply and controlled by U1050B
and Q1030.
The +0.6 V supply is adjustable via R1042 to allow the offset of the step generator
to be zeroed out. CR1040 temperature compensates the +0.6 V supply against
variations in the hybrid. The test points for these supplies are as follows:
+5 V TP1083
–5 V TP1084
+12 V TP1080
–12 V TP1081
+0.6 V TP1030
Ground TP1082
Front Panel
The Front Panel Board consists of the following circuits for these controls:
H
Push Button Switches and Latches
H
Rotary Binary Switches
H
Resistive Shaft Encoders
H
Analog-to-Digital Converter for Shaft Encoders
The Front Panel Board consists of the following circuits for the display module:
H
Electroluminescent Backlight Switch and Power Supply
H
Display Heater Circuitry
H
Display Drive Voltage (Contrast) Temperature Compensation
The Front Panel Board contains most of the instrument control as well as some
circuitry for the display module. A block diagram of the Front Panel Board is shown
in Figure 5–13 (next page).
The push button switches are normally open momentary switches When depressed,
these switches tie the inputs of NOR gate latches U3021, U3022, and U3023 to +5
VDC, setting the latches. The latches are reset by control signal ADCRD. The
processor updates the instrument configuration by periodically reading the state of
the latches through multiplexers U2024, U3025, and U3031.
These switches control:
H
MENU
H
VIEW INPUT
H
VIEW STORE
H
VIEW DIFF
H
STORE
Introduction
Push Button Switches and
Latches
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