Mutoh tech with Err 79 commu.

CR Encoder error means either the encoder sensor isn't plugged in, it's not straddling the encoder strip, or it's just broken.

Error 79 means the cable between the main board and heater junction board isn't plugged in or one of the boards is failing to communicate. The cable looks like an ethernet cable so it should be easy to spot.

 

It possible main firmware and heater control board firmware are not compatible. Wrong protocol can cause the problem.

 

Just for Information:
If CR encoder error appears on bootup sequence it mean main board does not receive correct information form CR encoder sensor during self check. If you pay attention then you will notice in first 4-5 sec of initialization process main board send PWM signal to PF motor then to CR motor. CR motor will turn fraction CW and then CCW at this moment main board checking respond from CR encoder sensor. If it correspond to motor rotation then it pass the test if not CR encoder error.
Now there are possible problems:
1. Encoder strip damaged or encoder sensor unplugged or it out of position. In this case carriage will jump and stop then error appear.
2. One of the Quadrature channel is damaged on the Encoder sensor and it not reading A and B phase correctly. It easy to check via diagnostic mode. You need to run encoder (CR test ) and move carriage by hand from right to left and check on control panel value should increase and decries according carriage direction
3. Encoder signal transmit to a main board via CR cables which link CR board an main board. In some cases damaged CR cables may triggers this issue.
4. Blown 2.5mA fast blown fuse on main board near CR cables. If fuse blown more likely you have damaged CR cables
5. damaged CR board. usually it happen if issue with CR cables.
Now if you do not have any carriage movement then it mean main board does not provide PWM to the motor. there are only few options:
1. CR motor cable not connected to a main board or damaged.
2. faulty CR motor
4. damaged main board (blown CR motor driver on the main board)

Serial number is not related to a CR encoder error as well as a heater junction board. In some cases (with some manipulations) you can remove this heater board from printer and it will works (without heating)