Nakamura tome TW10 locking and unlocking the c axis

Hi I'm working on a nakamura tome tw 10 and on the left side the service guy has replaced the spindle belts and also the the I think c axis encoder belt. Now the left side will not lock the c axis. You can turn off the power off and back on again and the c axis will rotate and find home and the m91 code will lock the c axis in place so we can create a saw slot in our part then it will unlock by way of m41 and it will run up to 20 parts and the left side c axis will stuck on m91 while it's trying to lock it. When replacing the c axis encoder belt does it have to be re timed? Thanks in advanced
Frankie