TC reported difficulties shifting the MCH away from B3 in ATPM. TC attempted to toggled the MCH seve ral times to shift away from B3. ~~~~~ 3559 when in depot, MCH stuck at B3 when MS was held down beyond ATPM. Removed cab console panel & checked all pins/bearings - OK. Found MS when shifted beyond ATPM will cause the lever & shaft to shift out of MS gear plate, thus causing MCH to interlock. Function check MCH & MS - OK. Notif 2415414 raised to SIG L to install inhibitor below ATPM.  Lee JC. 07/09/2022.    Notif 2415414. 3559 - TO INSTALL INHIBITOR BELOW ATPM MODE AT THE MS.