AC servo motor project - encoder problems

I have an AC servo motor from Yaskawa USASEM-08TV12 which I am trying
to control with a Yaskawa servo amp. The amp is giving an error that
the encoder is not wired correctly. Fortunately I have 2 amps and
motors. The second one is functioning. With an oscilloscope I have
examined the outputs from both encoders and they are identical on
Phase A, and B. The good motor has a Phase C output that pulses at a
rate similar to that on the other 2 phases. However, the new motor
that I am trying to get to function has an origin pulse once per
revolution. Thus the only difference I can see between the two
encoders is on the Phase C channel.

It does not seem that this phase C difference between the motors is
the problem however. There is also a monitor feature that displays
internal conditions on the amp. The display shows activity on the
Phase A,B,C channels on both motors but the Phase U,V,W channels are
silent on the problem motor's amp. I think Phase A,B,C represent
pulses to the motor and Phase U,V,W are encoder outputs but I am not sure.

The new motor is larger than the old one and it is possible that this
is causing the error but the error is encoder related and not overload
related.

The voltages on the encoder outputs from both motors are 3.9 volts
high and .39 v DC low so they seem adequate to drive TTL logic circuits.

One thing we are going to try is to build some inductors to limit the
current on the motor to see if that will stop the error. I have an LCR
meter and measure the inductance at 5mH at 1kHz and have calculated
that I need about 1.5mH per phase to make this 771 kW (1Hp) motor look
like a 420 kw (.6Hp) motor.

I know this is a complex post but hopefully there is someone out there
who might be able to shed some light.

Thanks,
Keith Clark