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 TM 10-3930-609-35
Table 2-1. Troubleshooting
Malfunction
Probable cause
Corrective action
Electrical
1. No travel motor torque, with SCR
a.
Neither relay IF nor IR will pick
a.
Make the following checks in order:
control (relay 1A open).
up-no control voltage from wire
(1) Check fuse IFU and replace if
69-2 to wire 13A.
burned out.
(2) With fuse IFU removed, use an
ohmmeter to check continuity
through the battery switch, panic
switch, seat switch and relay IMS
coil. Check IMS contacts.
Replace defective components
b.
Either relay IF or IR will not pick
b.
With drive wheels of truck off the
up with control voltage present.
floor, make the following tests as
required:
(1) Connect jumper from battery
positive to positive side of F or R
coil. If relay does not pick up,
check coil continuity with an
ohmmeter and replace if open
jumper to negative side of coil to
check for open circuit.
(2) With jumper on battery positive,
connect other end to wire 74 on
F interlock or 72 on R interlock.
If coil does not pick up interlock
is defective. Interlocks (fig. 3-23)
can be replaced without
removing relay.
(3) If trouble is not found, use
jumper to continue checking coil
energizing circuit components.
c.
Relays IF and IR close but there is
c.
With drive wheels of truck off the
no power or SCR hum with accelerat-
floor, make the following tests as
ing control depressed to SCR range.
required:
(1) With IF or IR picked up and
wire 45 disconnected at SCR ter-
minal board, use voltmeter to
check for positive control volt-
age between wire 41 and SCR
terminal board and wire 13A
(negative). If voltage is zero,
check IF or IR normally open
interlocks and 1A coil for con-
tinuity.
(2) With IF or IR picked up and
wire 4-5 disconnected at SCR
terminal board, use voltmeter to
check for positive control volt-
age between 1REC heat sink
(wire 25) and wire 13A (nega-
tive). If voltage is zero, check
fuse FUB, continuity of wiring
from battery positive to 1REC
heat sink, and F or R main con-
tacts. Repair or replace relay
contacts if defective and inspect
2-4
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