Inverter Repairs

TM 11-6130-377-14

CAUTION

(4) Disconnect the electrical connector A1P1

In (16) below, do not apply excessive

from its receptacle A1A2J1 on the inverted drive circuit

board A1A2.

pressure to the heat sinks when final

tightening the clamp nuts or this will

(5) Remove the four screws securing the

damage the SCR's.

inverter drive circuit board A1A2 and remove the board.

(6) Remove ten screws, lockwashers, and flat

washers securing the heat sink duct cover to the head

(16) Using a ratchet handle and inch deep

duct and remove the cover.

socket, alternately tighten each nut one-quarter turn at a

time until both nuts have been rotated no more than one

(7) To check A1Q2 (A1Q4), disconnect wire

and one-quarter turns. (The clamp nuts will not be

40 and the large heat sink, the A1Q2 (A1Q4) cathode.

snugged up any tighter, but the proper pressure will

(8) To check A1Q3, disconnect wire 113 from

have been applied to the SCR's.)

A1L5-2, measure the resistance between wire 113 and

(17) Install the heat sink duct cover on the

the large heat sink (cathode A1Q1 (A1Q3)).

heat sink duct and install the ten screws, lockwashers

(9) If short is indicated while performing step

and flat washers. Tighten screws to secure cover.

(7) or (8), complete steps (10) through (22) to replace

(18) Install the inverter drive circuit board

defective thyristor. If no short is indicated reconnect the

A1A2 on the four standoffs and secure with four screws

wires to their respective components.

and lockwashers.

(10) Loosen the nuts securing the SCR clamps

(19) Install the electrical plug A1P1 into the

using a ratchet handle and 1/2 inch deep socket. The

receptacle A1A2J1 on the inverter drive circuit board

clamps go through both halves of the heat sink.

A1A2.

(20) Position top cover in place and align

NOTE

screw holes. Install 12 screws and lockwashers and

The SCR may be held on the small

tighten screws.

heat sink by a centering pin and

(21) Close front indicator panel and secure

must be pulled off the heat sink.

with four captive screws.

(22) Perform a functional verification (para 6-

(11) Loosen the clamps just enough to slide

22) of inverter to check for proper operation.

the SCR from between the heat sinks.

Do not

b. Diodes A1CR4 (A1CR6) and A1CR5 (A1CR7).

completely remove nuts from stud.

(12) Cut the gate (white) lead, and pull out the

(1) Position the DC circuit breaker A1CB1 to

catholode (red) lead, from the SCR. Connect the new

OFF.

SCR to the leads going to P3, red connector.

(2) Open front indicator panel.

(13) Redistribute

the

silicone

dielectric

(3) Disconnect the electrical connector A1P1

compounds on the heat sink surfaces and apply a small

from its receptacle A1A2J1 on the inverter drive circuit

amount of compound to both side of the SCR.

board A1A2.

(14) Replace the SCR on the small heat sink

(4) Remove four screws securing the inverter

by snapping it onto the centering pin. The SCR surface

drive board A1A2 and remove board.

with the red lead attached must be next to the large heat

(5) Remove ten screws, lockwashers and flat

sink.

washers securing heat sink duct cover to heat sink duct

and remove the cover.

NOTE

(6) Disconnect the anodes (diode flex leads

The two heat sinks must remain

bolted together) and wires No. 49, 42, and 43 attached

parallel

during

the

tightening

to diodes A1CR4 (A1CR6) and A1CR5 (A1CR7). On

operation.

A1CR4 (A1CR6), disconnect wire 32; on A1CR5

(A1CR7), disconnect wire 34.

(15) Run the clamp nuts down evenly and

(7) Measure the forward and reverse

tighten finger tight.

resistance of each diode. Replace the diode which is

shorted. To replace a shorted diode proceed with the

following steps.

Change 1

6-8