TM 9-4120-404-14
3-37. LOGIC BOX ASSEMBLY (LGC). - Continued
b. Test. To test the logic board assembly a test fixture must first be prepared. After fabrication of the test fixture
assembly the logic board assembly can be tested using the following procedure.
(1) Test Equipment. The following test equipment is required to test the logic box assembly. The physical
configuration of the test fixture indicated is left to maintenance personnel as long as the circuit used conforms to Figure F-
3 in Appendix F.
Multimeter.
12 VDC regulated power supply.
Test fixture
(2) Set Up. Set up the above test equipment in accordance with the following steps.
(a) Adjust the DC power supply to + 12 0.5 volts DC.
(b) Turn it off and connect it to the test fixture where indicated.
(c) Connect the multimeter, positive lead, to TP1 and set it on a scale to read at least 12 volts DC.
(d) Connect P1, P2, and P3 to J1, J2, and J3, respectively, of the unit under test.
(3) Test Requirements. Failure of the logic circuit card assembly to meet any step in the following test
procedure constitutes failure of the entire assembly. Because no repair is authorized for a defective logic board
assembly, any logic board assembly that fails any portion of this test must be discarded and replaced with a new logic
board assembly.
(4) Test Procedures.
(a) Heat Mode Test.
1. Set temperature potentiometer, R6, to warmest position, mode switch, S7, to "H", and all fault
switches S1-S6, to "OFF" position (contacts closed), then apply power to power supply. After a
2-second delay, LED's 1 and 7 shall illuminate, and multimeter shall read + 12 .5 VDC on test
point, TP1, with respect to power supply common/board ground.
2. Set temperature potentiometer, R6, to coldest position. LED 1 shall turn off. LED 7 shall remain
illuminated.
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