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MAINTENANCE
WJ-8718A/MFP
a.
The front panel description in paragraph 2.4.4.
b.
Schematic Diagrams for the Front Panel Switch/Encode
Assembly (Figure 6-2), the
Front
Panel Switchboard
(Figure 6-4), the Front Panel Encode Board (Figure 6-3),
and the MFP Option, Main Assembly (Figure 6-9).
c.
Location of Component Diagrams, Figures 5-6 through
5-8.
d.
The circuit descriptions in paragraph 3.1.2.
e.
The microprocessor system troubleshooting procedures in
paragraphs 4.1.4 and 4.1.4.4.
2.
If the problem is confined to a single switch, suspect the switch
itself.
Vnplug the board behind the front panel, and use unpowered
ohmmeter measurements of track and solder connections between the
switch and the Front Panel Encode Board to isolate open or shorted
circuits.
3.
An LED display problem which appears heat related (for example, the
loss of segments after the unit has been in operation for some time)
may be
corrected
by
adjusting
the VR voltage.
Refer
to
paragraph 4.1.2.1 for the adjustment procedure.
4.
If all switches and LEDs are malfunctioning, verify the 1 MHz CLK
input to
VI
and U2 on the Front Panel Encode Board.
The
components associated with the CLK signal are
VI3E, VI3F,
R7, and
Cll.
5.
If a problem is confined to either the Group 1 or Group 2 switches
and LEDs, switch the socket-mounted
VI
and
V2
interface ICs and
note any changes in operation. If the problem symptoms disappear,
replace the defective IC. If symptoms persist, proceed to the next
step.
6.
If the problem is associated with all switches in a particular row or
column, proceed to troubleshoot circuits common to the row or
column.
Tables 4-2 and 4-3 identify the Group 1 and Group 2
switches.
A common R code within a group identifies switches by
row, and a common C code within a group identifies switches by
column.
a.
During operation, the inputs to column drivers
V12
(Group 2) and U11 (Group 1) should count in binary from 0
through 7 and the outputs should toggle.
If an oscillo-
scope probe is connected to the suspected row or column
line during execution of the BITE program, activation of a
switch in that row or column should cause a change in the
oscilloscope display.
4-26
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