D-16 Chadwick-Helmuth A Business Unit of Honeywell International, Inc.
Appendix D - 8520CS Signal Selector
D.7 Maintenance and Repair
D.7.1 Signal Selector 8520CS Disassembly (Figure D-11)
D.7.1.1 Controller Board and Signal Conditional Board Assembly
a. Turn unit upside down, remove eighteen screws (5) and washers (7), and remove bottom
cover (12).
b. Disconnect nine connectors from the assembly. On Signal Conditioning board J2, J4, J5,
J8, J11 and two 2 pin connectors going to front panel LED lights. On Controller board J5
and J8.
c. Remove six screws (19) and spacers (15) and remove Controller Board and Signal
Conditioning Board Assembly.
d, Remove the dual board assembly.
e. Pull apart the two boards by disconnecting them at the J3, J5, J7, J9 and J10 on Signal
Conditioner Board.
D.7.1.2 Power Supply Board A2
a. Disconnect three connectors (J1, J2, J3) from power supply board A2.
b. Remove four hex nuts (6) and two spacers (9), and remove power supply board A2 from
chassis (11).
D.7.1.3 Harness Asseblies
The harness assemblies consist of the parts that remain in the chassis after the circuit boards have been
removed.
D.7.2 Reassembly
NOTE: Harness dressing and routing are important to ensure proper operation and fit.
Follow original factory routing.
D.7.2.1 Power Supply Board A2
a. Install power supply board A2 on chassis (11) and secure with four 4-40 nylon lock std.
hex nuts (6) and 2 #4 clear rnd. 1/4” o.d standoffs (9).
b. Connect three connectors (J1, J2, J3) to power supply board A2.
D.7.2.2 Controller Board and Signal Condtioner Board Assembly
a. Connect the two boards together at the 5 headers J3, J5, J7, J9 and J10 on the Signal
Conditioner board. Align the connector pins on the Controller Board with the sockets on
the Signal Conditioning Board and carefully connect the two.
b. Install the two board assembly on the chassis and secure using 6 screws (19) spacers (15).
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