Watkins-Johnson Company WJ-8718A/MFP Instruction Supplement page 131

MAINTENANCE WJ-8718A/MFP
4.1.4.4
Front Panel Switch/Encode Assembly Modules (MFP- AI)
The Front Panel Switch/Encode Assembly consists of two subassemblies, intercon-
necting track, and amplifiers for the front panel phones jack. The two-channel amplifiers are
discussed in paragraph
4.1.6,
Audio Signal Troubleshooting. The following discussion pertains to
the Front Panel Encode Board (MFP-A1A1) which contains the modular units associated with
the microprocessor system. TrOUbleshooting the second A7 subassembly, the Front Panel
Switchboard, is discussed in paragraph 4.1.5.
The Front Panel Encode Board interfaces the front panel switches, LED indicators,
and LED displays with the microprocessor. The board contains two symmetrical modules which
interface the two front panel switch matrixes, identified as Group 1 and Group 2 (refer to
paragraph 3.1.2.2). Modules 3 and 4 interface the rotation of the front panel tuning wheei and
the LINE AUDIO/SIGNAL STR meter functions with the microprocessor. Tables
4-13
and
4-14
provide all pertinent data concerning the Front Panel Encode Board modules. The tables should
be used in conjunction with the information in paragraph
4.1.4.4.1.
Troubleshooting the Front Panel Encode Board is required when switches with
common circuits on the encode board are malfunctioning.
4.1.4.4.1
4-20
Front Panel Encode Troubleshooting Procedure
1. Reference the following manual data to support Tables
4-13
and
4-14.
a. Circuit descriptions in paragraph
3.1.2.
b. Location of Components Diagram, Figure
5-7.
c. Schematic Diagram, Figure
6-3.
d. Modular troubleshooting concept, described in
paragraph
4.1.4.1.
2.
The BITE program can be used to verify the operation of the Front
Panel Encode Board or to isolate a problem to a section of the board.
By referencing Tables
4-13
and
4-14,
common circuits to Group 1 or
Group 2 switches and LEDs can be noted; allowing a problem to be
isolated to a defective module or to a defective IC within a module.
Paragraph
4.1.5.1
contains an evaluation of the BITE program,
relative to the front panel switches, LEDs, and logic circuits.
3. The symmetry of the Group 1 and Group 2 modules allows switching
of the socket-mounted Ies, providing a simplified means of isolating
defective circuits.
4.
During operation, the SLO through SL3 outputs of U1 and U2, and the
outputs of U4, U5, U6, U8, U9, and U10 should always be toggling.. If
an output is stuck high or low, a problem with the IC, solder
connections, Vcc, or ground is evident.