GE Corometrics 170 Series, Руководство по обслуживанию

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5-22 170 Series Monitor Revision C
2000947-004
Theory of Operation: Main Board Theory of Operation
Display Interface Module
The display interface consists of a data buffer (U14) for D0–D7 which interfaces to
the ICM7228A seven-segment LED driver IC (U1 on the display board), and D flip-
flop U3 which drives the ±1 UA segments through Q1–Q4 transistors. Data lines
have 100
Ω
series resistors (R524–R531) which help to reduce emissions. A diode
clamp device (U18) on the data bus is a used to protect against ESD to the display
area.
Figure 5-13 provides a block diagram of the display interface module.
Figure 5-13. Display Module Interface Block Diagram
Status/Switch Input Module
The status/switch input module consists of buffers U15 and U16 and series/parallel
elements for protection against ESD. The monitor membrane switch panel provides
11 switch closures to ground which are fed to 100 k
Ω
pull up resistors and through
10 k
Ω
series elements. Buffers U14 and U15 are further protected by capacitors to
ground and diode clamp devices U17 and U22. Two LEDs are present on the
membrane switch panel: the power LED is driven by +5 V through resistor R350;
the recorder LED is driven from PAL U4 through buffer U6 and resistor R351.
Figure 5-14 provides a block diagram of the status/switch input module.
Figure 5-14. Status/Switch Input Module Block Diagram
Display Board
Transistor Drivers
for Pressure
± Display
4
to Data Bus
Latch
Data Buffer
10
to Data Bus
Chip Select and Address
Data
Buffers
Membrane Switch Inputs
Recorder Status Inputs
to Data Bus