VF-1 A axis Z channel missing

Hi All, I recently borrowed a friend's rotary. His is a 17 pin and my machine is 14 pin. I worked out the connections but shortly afterward the rotary began faulting. After taking it apart I found the encoder wheel had been rubbing on the window and wore away the mask. Scratch one encoder. I found a new replacement but 1800 line rather than 2000 line (and 6mm shaft rather than 1/2"). He had a spare motor with a 1/4" shaft so I machined that one down and replaced motor and encoder.
So now the problem is A axis Z channel missing or Z fault. The strange part is it will work to a point and then fault. The Z channel is a once around marker so if it is not working it would fault immediately, not after 10° or 140°. It faults almost immediately if I manually step it at full speed (0.1) but usually not at 0.01.
I was able to go 360° on a test cut with rapids set at 25% but then it started faulting after several steps (58 divisions or just over 6° per step). At 100% rapid it will fault on the first step or when doing Zero Return.
The A axis encoder connection to the MOTIF board is different than the X, Y and Z in that those all go through a receiver board with AM26LS32PC quad RS422 line drivers before connecting to the MOTIF board. The A axis goes directly to the MOTIF board even though there is provision on the receiver board to take the A axis (but no headers and three resistors not mounted). The X, Y and Z encoder cables inside the machine are 11 pin, the A axis is 7 pin. I will not find where the other wires for the A axis should come from until I get full access to the back of the machine.
It appears there must be noise or low signal strength causing the fault. I do not know why they bypassed the receiver board with the A axis. Does anyone have the A axis wired through the receiver board (daughter board mounted on the MOTIF board)? Mine is an early machine (1024).
By the way, you cannot just pin for pin connect a 17 pin rotary to a 14 pin machine as wires were re-purposed.

Haas makes a 14 to 17 pin adapter cable. Used to have one myself. About 1 foot long and about $150.00.


Mike

Wow! That is a lot of modifications for a borrowed rotary.

Z and A axis go to the same chip on the MOCON board, I have seen an A axis Encoder short and take out the Z axis encoder.
Check the diagnostics page and watch to see if you are getting random Z channel signals for the A or Z axis. I have seen both randomly pulse causing instant alarms when the servos are enabled.

Cheers,

maybe you can throw some fadal parts in while you're at it








couldn't resist

I traced out the receiver board. Putting the A axis through it will require rewiring the MS connector. Haas left off the D and G wires internally. The H and M wires are unused on the X, Y and Z connectors and are used for the A axis brake on mine. So if I replicate the X, Y, Z wiring I can run the A axis through the receiver board so the RS422 in the encoder has the proper receiver on the machine end.
The receiver board needed three 200 Ohm resistors and two headers added.

So to add to the above, I rewired the A axis internally to replicate the XYZ wiring to the receiver board. Same problem, A axis Z channel fault. Since they are all the same internally I connected the Z servo cable to the A axis input, turned On the Z only parameter (no home) and copied the Z axis parameters to the A axis. The Z servo would not home with the same Z channel fault. So the problem is not necessarily in the rotary. I pulled the receiver board and checked the output of the RS422 receivers, 0.5 volts. The specification sheet says 2.7 volts minimum. Although I measured the same 0.5 volts at the XYZ outputs the motor interface board the XYZ servos work but not the A axis. The motor interface board has additional 1K pullup resistors on the three A axis outputs tacked on externally, possibly as a bandaid to increase the output swing.
So the next check is to buy new AM26LS32 receivers and see if that fixes the problem. I will replace the XYZ receivers since their output is below specification also.