Taylor-Dunn B0-254-48 Operation, T Roubleshooting And Replacement Parts Manual page 163

Test 3. THE VEHICLE RUNS IN ONE DIRECTION ONLY
Test 3.1:
Close the seat switch, turn the key switch ON and
wait 1-second until the Isolator contactor closes.
If the vehicle runs in reverse only then skip
ahead to test #3.3.
Place the forward and reverse switch in the
FORWARD direction.
Test the voltage at pin #2 on the 12 pin logic card
connector.
If the voltage is low, then skip ahead to test
#3.2.
If the voltage is high, then skip ahead to Test
#7.
TEST 3.2:
Test the voltage at pin #3 on the 12 pin logic card
connector.
If the voltage is high, then skip ahead to test
#3.3.
If the voltage is low, then skip ahead to Test
#7.
TEST 3.3:
Place the forward and reverse switch in the
REVERSE direction.
Test the voltage at pin #3 on the 12 pin logic card
connector.
If the voltage is low, then skip ahead to test
#3.4.
If the voltage is high, then skip ahead to Test
#7.
TEST 3.4:
Test the voltage at pin #2 on the 12 pin logic card
connector.
If the voltage is high, then it is likely that the
internal directional control transistors have
failed, test the transistors at Test 3.5 and 3.6.
If the voltage is low, then skip ahead to Test
#7.
Electrical Troubleshooting
TEST 3.5
Disconnect the batteries and remove wires from
the B-, F1, and F2 terminals on the controller.
Using the diode test function on your meter, connect
the positive lead to the B- terminal on the controller.
Connect the negative lead to the F1 terminal on the
controller.
The test should show the presence of a diode
(approx 0.5v).
If the test is good, then skip ahead to test
#3.6.
If the test is open or shorted then one or both
directional FET's are shorted and the
controller must be replaced.
TEST 3.6
Disconnect the batteries and remove wires from
the B-, F1, and F2 terminals on the controller.
Using the diode test function on your meter,
connect the positive lead to the B- terminal on
the controller.
Connect the negative lead to the F2 terminal on
the controller.
The test should show the presence of a diode
(approx 0.5v). If the test is open or shorted
then one or both directional FET's are
shorted and the controller must be replaced.
STOP
Stop, do not continue. Reaching this point
indicates a failure in the Sevcon power unit
or an error was made during testing. Confirm
all previous tests were performed correctly
before replacing the Sevcon power unit.
Sevcon Troubleshooting
Page 9