Agilent Technologies 4284A Service Manual page 129

4-15. A9, A13, A90, AND A91 BOARDS SERVICE SHEET
4-15-1. CIRCUIT DESCRIPTION
The A9 keyboard consists of Key switches, LED indicators, a buzzer, and the LCD contrast
potentiometer. T h e A13 DC-AC Converter Board converts ±12 V DC into 600 V AC to sup-
ply the 600 V AC to the A91 LCD Module board to backlight the LCD. T h e A90 Keyboard/
Display Control Module board interfaces the A7 CPU board to both the A9 Keyboard and the
A91 LCD module board. The A91 LCD module is the HP 4284A's display screen.
4-15-2. TROUBLESHOOTING AIDS
Fuse A9F1 for the A90 board and is located on the A9 Keyboard. I f the HP 4284A display
screen isn't active, check fuse A9F1 first.
The A90 and A91 board assemblies aren't repaired at the component level because the
components on each board are surface mounted, and they are difficult to be replace. Thus,
A90 or A91 are faulty, repair them at the assembly level only.
4-15-3. REPLACEABLE PARTS LISTS
The replaceable parts for the A9 Keyboard are listed in Table 4-A9/A13/A90/A91-1. T h e
replaceable parts for the A13 DC-AC Converter are listed in Table 4-A9/A13/A90/A91-2. T h e
replaceable parts for the A90 Keyboard/Display Control and the A91 LCD module are listed
in Table 4-A9/A13/A90/A91-3. T h e A90 and A91 boards are repaired at the assembly level
only, because the components on each board are surface mounted, and are difficult t o
replace. S o , only the complete assembly part numbers are listed in Table 4-A9/A13/A90/
A91-3.
4-15-4. COMPONENT LOCATIONS
The component locations for the A9 Keyboard and the A13 DC-AC Converter board are
shown in Figure 4-A9/A13/A90/A91-1. Component locations for the A90 and A91 boards are
not shown because these boards are repaired at the assembly level only.
4-15-5. SCHEMATIC DIAGRAMS
The A9 Keyboard, A13 DC-AC Converter, A90 Keyboard/Display Control Unit, and A91 LCD
Module schematic diagrams are shown in Figure 4-A9/A13/A90/A91-2.
4-A9/A13/A90/A91-1
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