PS
S5.3
5230
001
Version no
T-code
F-code
Section
C-code
SCR Component Checks
180
Service Manual
1997-04-15
2. Capacitor 1C
Disconnect the battery and discharge the capacitor. Measure
ohms Through the capacitor using the Rx10,000 scale. Meter
should read zero and the swing slowly to above 100,000
ohms. Replace the capacitor if above reading is not obtained.
3. Contactors Forward, Rearward, 1A,
Power Steering, and Pump
150 ampere contactors instruction sheets.
300 ampere contactors instruction sheets.
4. Potentiometer in Accelerator
To check operation of potentiometer, disconnect the battery
and disconnect the wire #29 at control card TB1. Connect a
VOM to the wire that was removed from TB1 and to negative.
Place the VOM on the Rx100 scale. With the accelerator in
the creep speed position, the ohms reading should be 4800
to 6000 ohms. With the accelerator in the top speed position,
the ohm reading should be 50 ohms or less. With the wire
disconnected as above, check for resistance of 1 megohm or
higher from pot wire to the truck frame.
5. SCR’s (1REC, 2REC, 5REC)
These are silicon controlled rectifiers. Before checking,
disconnect the battery and discharge capacitor 1C.
Disconnect gate leads of SCR’s at the SCR terminal.
NOTE! Control is arranged so that the forward and
rearward contactors do not break current.
Check to see that the 1A contactor drops
before the forward and rearward contactor.
NOTE! Most contactor coils are polarity sensitive.
The left-hand terminal must be connected to
positive.
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