TM 10-8145-222-23
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REPAIR CONTINUED
Test Diode Block
There are three diode blocks in the MPC box, DB1, DB2, and DB3. Each diode block contains eight diodes connected
as illustrated in Figure 2. Diodes are labeled on the electrical schematic (FO-1) using a two-digit format, for example
36. The first digit represents the diode block associated with the diode and the second digit represents the individual
diode in that block, so diode 36 would be the sixth diode in DB3. The number 9 terminal on each diode block is
common to all diodes contained within that diode block.
If a diode is suspected to be faulty, test as follows
1. Pull diode block (Figure 6, Item 11) straight out from diode block socket (Figure 6, Item 12).
NOTE
A diode can be tested using an analog meter or a digital meter, but the testing
methods are different, as a digital meter will not indicate an accurate resistance
reading for a diode. A digital meter has a diode tester function. Both methods are
provided below.
2. If using an analog meter (Figure 7, Item 1), set meter to Rx1 scale and check between pin 9 (Figure 7, Item 2)
and suspected faulty diode pin in both directions.
A good diode will read very low resistance in one direction and very high resistance in opposite direction. If
not, replace diode block per this WP.
3. If using a digital meter (Figure 7, Item 3), set meter to diode test scale and check between pin 9 (Figure 7,
Item 4) and suspected faulty diode pin in both directions.
A good diode will read 0.4 0.7 V in one direction and open circuit or OL in opposite direction. If not, replace
diode block per this WP.
4. If diode block test is good, reinstall diode block (Figure 6, Item 11) into diode block socket (Figure 6, Item 12).
5. Operate unit, if required, in accordance with normal operating procedures to verify proper operation after
replacement of diode block (TM 10-8415-222-10, Operating Procedures).
6. Place MTRCS back into desired mode of operation (TM 10-8415-222-10, Operating Procedures).
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