Hi,
I too have a 322 building in MESA 7I76 and 7I77 to replace the controller
Did you conclude what the 21V AC was for?
Hello fellow 322 owner! You're in for a ride with all those solenoids... What kind of solenoid drive modules does your machine have? The RS485 ones or relay boards in the cabinet?
If I remember correctly, the 21 V AC going into the old controller (RT480 in my case) was just connected to a relay on the old controller's power supply and passed through to some safety device. In case the controls PSU has a failure, the machine wouldn't switch on.
I removed the RT480 controller entirely and permanently connected cable 122 to 123, that were going into the larger green connector.
I did end up using P2, P3, P4 as high-current power supplys for the Mesa 7i66 and 7i64, despite them being possibly switched by E22, the key switch at the cabinet front door (which I don't have a key for anyways) and KE2 (a contactor at the bottom right in the cabinets backside). The cards get their power via SmartSerial from the 7i94 and P1, only the high-current inputs get the other Ps. So far I got away with it, but can't recommend or advise against it.
