Figure 3-18. Transistor terminal identification

identification.

(2) To determine transistor leakage, check on a

(e) Reconnect encapsulated resistors on

transistor checker.

h. Diode Bias Block Test. Check each diode in the

collector bus bar and emitter leads on emitter bus bar

diode bias block for forward and backward resistance

(28).

(f) Reconnect all electrical leads and

using an ohmmeter. (fig. 3-1 and 3-16.) Backward

resistance must be about 10 times higher than forward

check for possible wiring errors.

resistance.

3-10. Capacitor and Diode Assembly

i. Inspection of parts.

a. Inspection.

(1) Inspect all parts for general condition and

(1) Inspect the capacitor and diode assembly for

signs of overheating and oxidation.

dust, dirt, and other foreign material. (fig. 3-14.) Pay

(2) Check electrical leads for frayed or

particular attention to the areas between the fins of the

deteriorated condition.

heat sinks.

(3) Check printed wiring board for cracks or

(2) Check for any evidence of damage such as

other damage. If in doubt, check printed wiring for

capacitor leakage, overheating, and arcing.

continuity.

b. Test. Test the capacitor and diode assembly

(4) Measure board mounted resistors and

using an ohmmeter. Disconnect battery and discharge

encapsulated resistors using an ohmmeter and milliohm

capacitors (para2-5I. Tag and disconnect all leads

meter.

coming to terminals Al, A2, B2-, and B2+. (fig. 3-19.)

j. Reassembly.

Reconnect the leads after the test.

(1) Reassemble an individual power switch

(1) Measure forward resistance of diode D 1 by

module in the reverse of the order shown in figure 3-17.

connecting ohmmeter between terminals Al (-lead) and

Note. Use silicone grease between the

B2- (+lead). Note reading.

transistors and their heat sinks when

(2) Measure D1 backward resistance by

assembling.

reversing

the

connections.

Backward-to-forward

(2) Reassemble the power switch assembly in

resistance ratio should be at least 10 to 1.

the reverse of the order shown in figure 3-15, and as

(3) Measure forward resistance of diode D2 by

follow s.

connecting ohmmeter between terminals Al (-lead) and

(a) Assemble power switch modules on

A2 (+ lead). Note reading.

mounting rods 147) between end plates.

Position

(4) Measure D2 backward resistance by

spacers (44) between power switch modules.

reversing

the

connections.

Backward-to-forward

(b) Tighten nuts (42) at both ends of

resistance ratio should be at least 10 to 1.

insulated mounting rods.

(5) Disconnect the D3 lead from the capacitors.

(6) Measure forward resistance of diode D3 by

encapsulated resistors (33) and on top of modules.

connecting ohmmeter between terminal Al (- lead) and

(d) Align holes in collector bus bar and

the D3 lead (+ lead). Note reading.

install and tighten attaching hardware terminal

3-29