Hello-
After several months of inactivity on my 1981 Mycenter 2, I attempted to power up and exercise the machine. Machine powered up, but Fanuc 6m-b control went into an immediate 426 Y axis alarm (Y axis Fanuc pulse coder position feedback is abnormal - Disconnection alarm). Immediately contacted my friend/mentor in the CNC world and he told me to check all associated contacts which I proceeded to do. Here is an interesting observation that perhaps someone can weigh in on: With power off, I have found that I can get the machine to respond normally after I press the small black contactor button in multiple times on the Y axis drive unit (Fanuc A06B-6045-H001/H002) and then power the machine on. This work-around only lasts for a short period of time (from 15 seconds to many minutes) and there appears to be a correlation between how many times I exercise the contactor button and how long normal operation lasts. I have carefully accessed the Y axis servo and reseated both canon plugs as well as checked the brushes (which look great).
With that being said, I replaced the existing Y axis drive with another used drive and received the same alarms (401, 420, 422 & 426 which ALL go away after exercising the contactor button), so I don't believe the drive is the issue. I think that the exercised contactor button is having an electrical effect in some other part of the control or power supply that is causing the machine to function normally for a short period of time. Any thoughts and experiences are welcomed to root out the cause! Thank you.