Mitsubishi Electric PUMY-P200YKM2 Technical & Service Manual page 76

Check code
Signal communication error with transmission processor
6606
(A6)
Abnormal points and detection methods
If the data of unit/transmission processor were not normally transmitted.
If the address transmission from the unit processor was not normally
transmitted.
●Diagnosis of defects
Make sure to turn the power OFF before connecting/disconnecting any connectors, or replacing boards.
Turn the power OFF of indoor/outdoor unit, Fresh
Master, Lossnay and remote controller simultaneously
for 2 minutes or more, then turn the power back ON.
Does it operate normally?
OCH675D
Diagnosis
Yes
Causes and checkpoints
Accidental disturbance such as noise or lightning
surge
Hardware malfunction of transmission processor
Replace the controller
No
(Defect of error source controller).
There is no abnormality on the AC unit.
It might be caused by an external noise, so check
the transmission line to remove the factor(s).
76
Remedy