[DHG]

I bought a Bridgeport MDI with TNC 131 control earlier this year. I got it working and it was running last time I used it (about a month ago). I am now unable to home the Y-axis. When I power on, the Z homing routine works correctly, but Y doesn't. If I'm understanding the auto homing process correctly it goes as follows:

1) Check if the Y home switch (called CROSS REF. on the schematic) is held down by the cam. If it is, jog Y- until off the switch.
2) Move Y+ until the home switch comes on, then watch for the homing pulse on the encoder

My y-axis is completing step 1 successfully, so the CNC can see the home switch, but on step 2, it doesn't appear to be seeing the homing pulse. It just keeps moving in the Y+ direction until it hits the limit switch.

I thought that maybe the issue was that the home pulse wasn't occurring between hitting the home switch and hitting the limit switch, so I moved the table to the middle of travel and manually actuated the home switch. There was no difference even though I know the motor made a full revolution.

Is there a way to check if the encoder is putting out a home pulse? I have access to an oscilloscope if that will help.

Thank you,
Daniel

[gus]

If you are saying that it never stops when travelling in its initial direction then it never saw the switch. probably a bad switch or connection

[DHG]

It can see the Y home switch; if I manually position the axis over it, the CNC will jog Y- to get of the switch.

I think we've tracked the problem down to a bad Y encoder. We put a scope on the Z encoder (known good) and the Y encoder. The 0 degree waveform on Y is very weak and noisy. We're also seeing very different measurements on the photodiodes on Y vs. Z.