TM 5-4520-241-14
Table 5-1. Direct Support and General Support Troubleshooting - Continued
MALFUNCTION
TESTING OR INSPECTION
CORRECTIVE ACTION
4 - Continued
Step 2.
Test the PC board and transistor assembly. Remove the jumper installed in the female receptacle
in step 1. Plug the control box into the female receptacle, and reinstall the control box on the front
of the heater case. Set the room thermostat above ambient temperature to ensure that its contacts
are closed.
Open the control box cover. Remove nuts (1, fig. 5-7), lock washers (2), and flat washers (3)
securing label (4) to the PC board (15). Pull off the label for access to connection points on the
board.
Connect the power plug. Perform the following tests to evaluate the condition of the PC board and
transistor assembly.
CAUTION
Set up tests and make all test connections before switching the HEATER-OFF-FAN
switch to HEATER. All test readings must be made with only momentary actuation
of the switch to the HEATER position.
Connect a DC voltmeter to V5 (negative) and to the center pin of the transistor (positive). It may be
necessary to scrape away the varnish coating to ensure good contact. (Refer to Appendix D,
Expendable Supplies and Materials List.) Momentarily move the switch to HEATER. The voltmeter
must read approximately 30 volts. If it reads less than 28 volts, replace the PC board and transistor
as an assembly (see below).
Connect the voltmeter to V5 (negative) and V4 (positive). Scrape away the varnish coating if
necessary. (Refer to Appendix D, Expendable Supplies and Materials List.) Momentarily move the
switch to HEATER. The voltage should be 13 volts. If it is less than 12 volts, replace the transistor.
If it is more than 14 volts, replace the PC board and transistor as an assembly.
5-15
