Toshiba TMD-13 / Fanuc 15T Spindle Won't Orient

We have a Toshiba TMD-13 lathe w/ Fanuc 15T control that out of the blue won't orient the spindle, table orients correctly. It has a encoder built into the spindle motor as well as a separate belt driven encoder off the spindle draw tube. The bearings in the motor were getting noisy so they replaced the motor hoping that would also take care of the orientation issue but it didn't. Fanuc suggested the issue was with the belt driven encoder off the spindle so that was replaced, but it still won't orient. They checked both encoder cables for continuity and both were OK. It was then dumped in my lap.

The spindle drive is a Fanuc Model 12S #A06B-6064-H312. I tried swapping the serial interface boards (A16B-2201-0440) between the table amp and the spindle amp and there was no change - table orients, the spindle doesn't. The amp gets the orient command signal (G227.6 ORCMA goes HIGH), the spindle starts spinning in reverse at about 30rpm and keeps spinning until the machine times out because Orient Arrival (F229.7 ORARA) never goes high. M5 won't stop the spindle, I have to give it an M3 first, then M5 will stop the spindle when stuck in the orient loop. Spindle encoder uses 3 differential pairs, one each for A, B, and Z while the motor encoder just uses A and B phase differential pairs. The table and spindle both use motor and spindle/table encoders. Putting a scope on the A phase on the spindle encoder with the spindle spinning at 30 rpm I get a nice square wave ±1.2vdc (ground referenced to either A or ? phase) or 2.4vpp (between A and ?). Checking the A phase for the table encoder (table spinning @ 30rpm) I get the same thing but ±1.4vdc or 2.8vpp. The B phase amplitude is the same and lags A by 90°. Likewise, the Z phase has similar amplitude. Checking the A/B phases from the motor encoders I get nothing off either the spindle or the table checking from ground to A or ? or across A and ? (same for the B phase). The spindle motor is set up as the primary, the table motor is the secondary spindle. Checking parameter 3001, both MRDY1 and POSC2 are HIGH designating the MRDYA signal is used and it does use a position coder signal and both CAXIS2 and CAXIS1 are low designating it doesn't use the magnetic pulse coder or the pos. detect signal from the magnetic encoder. It's also interesting that if I unplug CN13 from the serial board for the spindle, nothing happens, but if I unplug CN13 from the table board, it throws an AL-27 Position Coder Signal Disconnection alarm. I confirmed that 3007bit5 was set to 0 (Position Coder Signal Detect Check - 0=Check 1=Don't Check) for the spindle and 3147bit5 = 0 for the table. If I set 3147b5 to a 1, then I can disconnect the encoder for the table and the drive won't throw the AL-27 alarm. One other thing I noticed, the display shows the commanded speed but is showing the actual speed as 0 for the spindle, but if I'm running the table it does display the actual speed.

I'm now pretty much out of ideas on what else to check so I'm hoping someone here can give me some ideas. I'd appreciate any help, even a decent overview of how exactly the 15 control handles orientation and what exactly the encoder inside the motor does and what the encoder driven off the spindle controls.

Marc --