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MX-7500N  TROUBLESHOOTING  7 – 33

 

 

 

 

 

 

Trouble content

Temperature detection is out of range. (Out of -28 to 
78 degrees C)

Detail

PCU

Cause

Transfer thermistor trouble.
Transfer thermistor connector connection trouble.
PCU PWB trouble.

Check & Remedy

Check connection of the connectors and harness of 
transfer thermistor.
Check PCU PWB.
Replace transfer thermistor or PCU PWB.

Trouble content

When executing the high density process control in 
the toner cartridge-less production process, the 
developing bias exceeds 500V.

Detail

PCU

Cause

•Image density sensor trouble, harness connection 

trouble between the PCU PWB and the image 
density sensor, dirt on the image density sensor, 
transfer belt cleaning trouble

• Developing tank abnormality

Check & Remedy

•Use SIM44-02 to execute the gain adjustment of the 

process control sensor.
•When “Error” is displayed, it may be considered as 
breakdown. Check the sensor and the harness.
•When the adjustment is normally completed, check 
the drum surface and the belt surface.

•Replace the developing tank.

Trouble content

When executing the high density process control in 
the toner cartridge-less production process, the 
developing bias exceeds 500V.

Detail

PCU

Cause

-  Image density sensor trouble, harness connection 

trouble between the PCU PWB and the image 
density sensor, dirt on the image density sensor, 
transfer belt cleaning trouble

-   Developing tank abnormality

Check & Remedy

-  Use SIM44-02 to execute the gain adjustment of the 

process control sensor.
When "Error" is displayed, it may be considered as 
breakdown. Check the sensor and the harness.
When the adjustment is normally completed, check 
the drum surface and the belt surface.

-  Replace the developing tank.

Trouble content

When executing the high density process control in 
the toner cartridge-less production process, the 
developing bias exceeds 500V.

Detail

PCU

Cause

•Image density sensor trouble, harness connection 

trouble between the PCU PWB and the image 
density sensor, dirt on the image density sensor, 
transfer belt cleaning trouble

• Developing tank abnormality

Check & Remedy

•Use SIM44-02 to execute the gain adjustment of the 

process control sensor.
•When “Error” is displayed, it may be considered as 
breakdown. Check the sensor and the harness.
•When the adjustment is normally completed, check 
the drum surface and the belt surface.

•Replace the developing tank.

Trouble content

When executing the high density process control in 
the toner cartridge-less production process, the 
developing bias exceeds 500V.

Detail

PCU

Cause

•Image density sensor trouble, harness connection 

trouble between the PCU PWB and the image 
density sensor, dirt on the image density sensor, 
transfer belt cleaning trouble

• Developing tank abnormality

Check & Remedy

•Use SIM44-02 to execute the gain adjustment of the 

process control sensor.
•When “Error” is displayed, it may be considered as 
breakdown. Check the sensor and the harness.
•When the adjustment is normally completed, check 
the drum surface and the belt surface.

•Replace the developing tank.

Trouble content

The after-transfer discharge lamp open sensor is kept 
open for a specified time from turning ON the after-
transfer discharge lamp.

Detail

PCU

Cause

Connection trouble between the after-transfer 
discharge lamp PWB and the PCU PWB
After-transfer discharge lamp PWB trouble
PCU PWB trouble

Check & Remedy

Use SIM5-4 to check lighting of the after-transfer 
discharge lamp (K) [DL2_K].
Check the after-transfer discharge lamp PWB (K).
Check the harness and the connector.
Replace the PCU PWB.

MX-7500N  TROUBLESHOOTING  7 – 34

 

 

 

 

 

 

 

 

 

Trouble content

The after-transfer discharge lamp open sensor is kept 
open for a specified time from turning ON the after-
transfer discharge lamp.

Detail

PCU

Cause

Connection trouble between the after-transfer 
discharge lamp PWB and the PCU PWB
After-transfer discharge lamp PWB trouble
PCU PWB trouble

Check & Remedy

Use SIM5-4 to check lighting of the after-transfer 
discharge lamp (C) [DL2_C].
Check the after-transfer discharge lamp PWB (C).
Check the harness and the connector.
Replace the PCU PWB.

Trouble content

The after-transfer discharge lamp open sensor is kept 
open for a specified time from turning ON the after-
transfer discharge lamp.

Detail

PCU

Cause

Connection trouble between the after-transfer 
discharge lamp PWB and the PCU PWB
After-transfer discharge lamp PWB trouble
PCU PWB trouble

Check & Remedy

Use SIM5-4 to check lighting of the after-transfer 
discharge lamp (M) [DL2_M].
Check the after-transfer discharge lamp PWB (M).
Check the harness and the connector.
Replace the PCU PWB.

Trouble content

The after-transfer discharge lamp open sensor is kept 
open for a specified time from turning ON the after-
transfer discharge lamp.

Detail

PCU

Cause

Connection trouble between the after-transfer 
discharge lamp PWB and the PCU PWB
After-transfer discharge lamp PWB trouble
PCU PWB trouble

Check & Remedy

Use SIM5-4 to check lighting of the after-transfer 
discharge lamp (Y) [DL2_Y].
Check the after-transfer discharge lamp PWB (Y).
Check the harness and the connector.
Replace the PCU PWB.

Trouble content

Detail

PCU

Cause

LUD1 is not turned ON within the specified time.
CLUD1 sensor trouble.
Paper feed tray 1 lift unit trouble.
PCU PWB trouble.
Sensor harness and connector connection trouble

Check & Remedy

Check connection of the harness and the connector of 
LUD1.
Replace the lift unit.
Replace the PCU PWB.

Trouble content

LUD2 does not turn ON within the specified time.

Detail

PCU

Cause

LUD2 does not turn ON within the specified time.
CLUD2 sensor trouble.
Paper feed tray 2 lift unit trouble.
PCU PWB trouble.
Sensor harness and connector connection trouble

Check & Remedy

Check the harness and the connector of LUD2.
Replace the lift unit.
Replace the PCU PWB.

Trouble content

C3LUD does not turn ON within the specified time.

Detail

PCU

Cause

C3LUD sensor trouble.
Cassette 3 lift motor trouble.
Harness connection trouble between the PCU PWB, 
the lift unit, and the paper feed unit

Check & Remedy

Check the harness and the connector of C3LUD.
Check the lift unit.

Trouble content

C4LUD does not turn ON within the specified time.

Detail

PCU

Cause

C4LUD sensor trouble.
Cassette 4 lift motor trouble.
Harness connection trouble between the PCU PWB, 
the lift unit, and the paper feed unit

Check & Remedy

Check the harness and the connector of C4LUD.
Check the lift unit.

Trouble content

Double feed sensor abnormality detection

Detail

Printer (section) PWB

Cause

Double feed sensor abnormality.
Harness / circuit trouble related to the double feed 
sensor.
Insertion failure of the drawer connector of the PS 
unit.

Check & Remedy

Check the circuit related to the double feed sensor 
and the harness and the connector.
Replace the double feed detection PWB and the sen-
sor.

Trouble content

Detail

PCU

Cause

Thermistor trouble
PCU PWB trouble
Thermistor connector and harness connection trouble
Fusing section connector connection trouble
Fusing unit not installed

Check & Remedy

Use SIM44-14 to check the state of the thermistor.
Replace the thermistor.
Replace the PCU PWB.
Check connection of the thermistor connector and the 
harness.
Check the connector in the fusing section.

MX-7500N  TROUBLESHOOTING  7 – 35

 

 

 

 

 

 

 

 

Trouble content

The thermistor is open.

Detail

PCU

Cause

Thermistor trouble
Control PWB trouble
Fusing section connector connection trouble
AC power trouble
Fusing unit not installed.

Check & Remedy

Check connection of the harness and the connector 
from the thermistor to the control PWB.

Trouble content

The thermistor is open.

Detail

PCU

Cause

Thermistor trouble
Control PWB trouble
Fusing section connector connection trouble
AC power trouble
Fusing unit not installed.

Check & Remedy

Check connection of the harness and the connector 
from the thermistor to the control PWB.

Trouble content

The thermistor is open.

Detail

PCU

Cause

Thermistor trouble
Control PWB trouble
Fusing section connector connection trouble
AC power trouble
Fusing unit not installed.

Check & Remedy

Check connection of the harness and the connector 
from the thermistor to the control PWB.

Trouble content

The thermistor is open.

Detail

PCU

Cause

Thermistor trouble
Control PWB trouble
Fusing section connector connection trouble
AC power trouble
Fusing unit not installed.

Check & Remedy

Check connection of the harness and the connector 
from the thermistor to the control PWB.

Trouble content

The thermistor is open.

Detail

PCU

Cause

Thermistor trouble
Control PWB trouble
Fusing section connector connection trouble
AC power trouble
Fusing unit not installed.

Check & Remedy

Check connection of the harness and the connector 
from the thermistor to the control PWB.

Trouble content

The thermistor is open.

Detail

PCU

Cause

Thermistor trouble
Control PWB trouble
Fusing section connector connection trouble
AC power trouble
Fusing unit not installed.

Check & Remedy

Check connection of the harness and the connector 
from the thermistor to the control PWB.

Trouble content

The thermistor is open.

Detail

PCU

Cause

Thermistor trouble
Control PWB trouble
Fusing section connector connection trouble
AC power trouble
Fusing unit not installed.

Check & Remedy

Check connection of the harness and the connector 
from the thermistor to the control PWB.

Trouble content

Detail

PCU

Cause

The fusing temperature exceeds the specified level.
Thermistor trouble
PCU PWB trouble
Thermistor connector and harness connection trouble
HL control PWB trouble

Check & Remedy

Use SIM44-14 to check the state of the thermistor.
Use SIM5-2 to check the flashing operation of the 
heater lamp.
Use SIM14 to cancel the trouble.
Replace the thermistor.
Replace the PCU PWB.
Check connection of the thermistor connector and the 
harness.
Replace the HL control PWB.

MX-7500N  TROUBLESHOOTING  7 – 36

 

 

 

 

 

Trouble content

Detail

PCU

Cause

The fusing temperature exceeds the specified level.
Thermistor trouble
PCU PWB trouble
Thermistor connector and harness connection trouble
HL control PWB trouble

Check & Remedy

Use SIM44-14 to check the state of the thermistor.
Use SIM5-2 to check the flashing operation of the 
heater lamp.
Use SIM14 to cancel the trouble.
Replace the thermistor.
Replace the PCU PWB.
Check connection of the thermistor connector and the 
harness.
Replace the HL control PWB.

Trouble content

Detail

PCU

Cause

The fusing temperature exceeds the specified level.
Thermistor trouble
PCU PWB trouble
Thermistor connector and harness connection trouble
HL control PWB trouble

Check & Remedy

Use SIM44-14 to check the state of the thermistor.
Use SIM5-2 to check the flashing operation of the 
heater lamp.
Use SIM14 to cancel the trouble.
Replace the thermistor.
Replace the PCU PWB.
Check connection of the thermistor connector and the 
harness.
Replace the HL control PWB.

Trouble content

The fusing temperature does not reach the specified 
level within the specified time from turning ON the 
power relay.

Detail

PCU

Cause

Thermistor trouble.
Heater lamp trouble.
PCU PWB trouble.
Thermostat trouble.
Connector, harness connection trouble.
HL control PWB trouble.
Power unit trouble.

Check & Remedy

Use SIM14 to cancel the trouble.
Use SIM44-14 to check the state of the thermistor.
Use SIM5-2 to check the flashing operation of the 
heater lamp.
Replace the thermistor.
Replace the heater lamp.
Replace the PCU PWB.
Replace the thermostat.
Check connection of the connector and the harness.
Replace the HL control PWB.
Replace the power unit.

Trouble content

The fusing temperature does not reach the specified 
level within the specified time from turning ON the 
power relay.

Detail

PCU

Cause

Thermistor trouble.
Heater lamp trouble.
PCU PWB trouble.
Thermostat trouble.
Connector, harness connection trouble.
HL control PWB trouble.
Power unit trouble.

Check & Remedy

Use SIM14 to cancel the trouble.
Use SIM44-14 to check the state of the thermistor.
Use SIM5-2 to check the flashing operation of the 
heater lamp.
Replace the thermistor.
Replace the heater lamp.
Replace the PCU PWB.
Replace the thermostat.
Check connection of the connector and the harness.
Replace the HL control PWB.
Replace the power unit.

Trouble content

The fusing temperature does not reach the specified 
level within the specified time from turning ON the 
power relay.

Detail

PCU

Cause

Thermistor trouble.
Heater lamp trouble.
PCU PWB trouble.
Thermostat trouble.
Connector, harness connection trouble.
HL control PWB trouble.
Power unit trouble.

Check & Remedy

Use SIM14 to cancel the trouble.
Use SIM44-14 to check the state of the thermistor.
Use SIM05-02 to check the flashing operation of the 
heater lamp.
Replace the thermistor.
Replace the heater lamp.
Replace the PCU PWB.
Replace the thermostat.
Check connection of the connector and the harness.
Replace the HL control PWB.
Replace the power unit.