之前有师傅在论坛里有回答过的这个问题 楼主可以参考下 报码后测试下下面对应的是那个传感器 好排除问题
机型: DC1100/900 4110 4112 4127
主题:如何查找造成77-909的故障代码
问题 ：
机器报77-909时，有时候在DC120、DC122里面查不到故障记录
原因：
软件设计
解决：
查看NVM 742-003(链码)和742-004(故障代码)就可以找到造成77-909的传感器代码
然后查手册 找到对应的故障代码，具体解决
E.g.: If the current value in NVM[742-003] is [77] and the current value in NVM[742-004] is [108], it indicates the cause is DC330[077-108]=IOT Exit Sensor. Turning OFF the power clears the values in NVM[742-003] and NVM[742-004]. The suspected sensors are as follows:
E.g.: If the current value in NVM[742-003] is [77] and the current value in NVM[742-004] is [108], it indicates the cause is DC330[077-108]=IOT Exit Sensor. Turning OFF the power clears the values in NVM[742-003] and NVM[742-004]. The suspected sensors are as follows:
[071-100] Tray 1 Pre Feed Sensor
[072-100] Tray 2 Pre Feed Sensor
[073-100] Tray 3 Pre Feed Sensor
[074-100] Tray 4 Pre Feed Sensor
[010-201] Fuser Exit Sensor
[077-105] Invert In Sensor
[077-106] Invert Path Sensor
[077-100] Trans Path Sensor 1
[077-101] Trans Path Sensor 2
[071-101] Feed Out Sensor 1
[072-101] Feed Out Sensor 2
[073-101] Feed Out Sensor 3
[074-101] Feed Out Sensor 4
[077-103] Pre Regi Sensor
[077-104] Regi Sensor
[077-107] Invert Out Sensor
[077-108] IOT Exit Sensor
[077-109] Dup In Sensor
[077-110] Dup Path Sensor 1
[077-111] Dup Path Sensor 2
[077-112] Dup Out Sensor
[075-100] MSI Pre Feed Sensor
[075-101] MSI Feed Out Sensor
Check the machine inside for pieces of paper.
Signal line from the sensor for a short to the frame
Check if the Sensor actuator improperly returns.
Sensor for light from outside
Check for a drop in the power voltage to the sensor.