(4) Disconnect the electrical connector A1P1
In (16) below, do not apply excessive
from its receptacle A1A2J1 on the inverted drive circuit
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 ½ 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.
(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.
(20) Position top cover in place and align
screw holes. Install 12 screws and lockwashers and
The SCR may be held on the small
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.
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
SCR to the leads going to P3, red connector.
(2) Open front indicator panel.
(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.
(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
washers securing heat sink duct cover to heat sink duct
and remove the cover.
(6) Disconnect the anodes (diode flex leads
The two heat sinks must remain
bolted together) and wires No. 49, 42, and 43 attached
to diodes A1CR4 (A1CR6) and A1CR5 (A1CR7). On
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.
shorted. To replace a shorted diode proceed with the