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2-44 Service Manual
5016-001
C 991 Service - Engine error.
Note: This error displays when a problem exists with the coupling
on and off sensors. The same error displays for either sensor.
FRU Action
1 Coupling On/Off
Sensors
Engine Board
SN Cable
Engine Board
Turn the printer on and observe how long it takes
for the error to display. If the coupling On sensor is
failing, the warm-up will be shorter than the
coupling Off sensor.
Check the sensors by manually positioning the
coupling cam disk over the coupling on (upper)
sensor while turning the printer on. If the disk
moves out of coupling, and the error displays,
there is a problem with the coupling On sensor. If
you manually position the coupling cam disk over
the coupling Off (lower) sensor, while turning the
printer on and the disk moves out of the Off sensor
and then moves back into the sensor, there is a
problem with the Off sensor.
Coupling On sensor
Pin # Signal Voltage Voltage
Voltage Cam Disk in Cam Disk Out
1 +5 V dc +5 V dc +5 V dc
2 CUPON +5 V dc 0 V dc
3 DGND 0 V dc 0 V dc
Coupling Off sensor
Pin # Signal Voltage Voltage
Voltage Cam Disk in Cam Disk Out
1 +5 V dc +5 V dc +5 V dc
2 CUPOFF +5 V dc 0 V dc
3 DGND 0 V dc 0 V dc
If a problem cannot be isolated with the sensors,
check the SN cable.
• If incorrect, replace the cable.
• If correct, replace the engine board.
2 Coupling Cam Check the coupling cam and associated parts for
correct operation. If a problem is found, repair or
replace the motor mounting stay A assembly.