Mesa 5i20 - 7i37TA - 7i48

or they are really just single ended encoders? you could use them that way if you can't fix the problem..

I thought of that but 1.77V is not a valid high TTL level

Though 1.77V from a single ended encoder trying to
drive the 7I48s 120 Ohm differential termination is a possibility

So if the encoders output a valid TTL high (>2.4V) if _not_
connected to the 7I48. I would try jumpering the 7I48 for TTL inputs...

Also just to make sure, I am assuming you have A+ --> 7I48.ENCA A- -->7I48./ENCA etc

Thanks for the diagnostic help. There are x,y,z connectors near the controller that bring the encoder wires into the control cabinet. By swapping the y plug onto the z and x connectors I could get the x and z dros to move using the y handwheel. This confirms to me that my wiring from the connectors to the 7i48 is ok. I ordered one new encoder. If it works I'll order a second. I'm having trouble getting the Z encoder off the machine. The coupling uses set screws that take a .050" hex key.

While I'm waiting for the new encoder to come in I decided to power up the y axis drive to see if I could make some progress there. Up until this point I had the fuses out so now power could reach the drives.

I put the y fuse in and brought linuxcnc out of estop. It immediately went back into estop with a joint 1 following error. I went into the ini file and increased the following error to .1 from .0005. Brought the machine out of estop the table moves approx .1 and then I get the joint one following error. I switched the motor leads to reverse the direction of rotation. Brought the machine out of estop and the table moves approx .1 in the other direction and then I get the joint 1 following error.

Any hints? I'm sure I need to do some reading but if someone could point me in the right direction I would appreciate it.

If these are velocity mode drives, you cannot simple swap the motor leads or you will a drive runaway independent of any external drive.

You can swap both motor and tachometer leads but I think its better to keep the original motor drive wiring and if the feedback is reversed use the OUTPUT_SCALE parameter (assuming this is that this is the hm2-servo sample config) reversing the sign of OUTPUT_SCALE should get you back to negative feedback

One other detail to check is that the PWM gens are in mode 2 (the 7I48 needs mode 2 = up/down mode PWM)

I believe I'm trying to run these drives in torque (current) mode. The drive is AMC 30a8.

www.a-m-c.com/download/manual/AMC_Analog...es_InstallManual.pdf - Manual
www.a-m-c.com/download/support/an-007.pdf - Running brushed motors
www.a-m-c.com/download/datasheet/b30a8.pdf - Data sheet

I confirmed that I'm in PWM gen mode 2.

I would set your FE range a little larger and set your I=0, D=0 and P = .1 or so
to first verify proper feedback direction.

There are a couple of possibilities here for what appears to be runaway, one is feedback direction. the other one is oscillation because the PID loop gains are starting out too high

By setting a low P gain. proper feedback direction can be verified

If this does not work, I would break the feedback loop (say disconnect the drives from the analog out) and verify that the analog outpu does the expected thing when LinuxCNC is started and the motor shafts are rotated away from their starting positions (the analog voltage should be proportional to the distance from the starting position (and the polarity should match the direction of motion from the starting position)

Update:

I had one of the pots on the drive turned the wrong way. With that corrected when I bring the machine out of estop the axis does not move. The motor is not yet holding the axis stationary but I checked the voltage between between + REF IN and - REF IN and I see a voltage which increases as I turn the handwheel. If I reverse the direction rotation the voltage goes back to 0 and then negative which seems correct.

I'm concluding that my drive set up is still not correct. I'll go back over the manuals to see if I can find any more set up errors.

Can you verify that the REF inputs change in such a way as to
drive the motor in the reverse direction of the displacement?

(This is the correct negative feedback configuration)

The motor isnt driving or holding the axis so I'm not sure how to verify that. The absolute value of the ref signal increases as I turn the handle in either direction.

is the drive enabled?
If a non zero input does not drive the motor you need to solve this first