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PSA: Intermittent Fadal 4020 X axis faults


Nov 17, 2023
For the last 3 years we've been running 2 vintage 2004 Fadal 4020 mills both with the Calmotion 527F control upgrade. About a year ago we started getting highly random X axis faults. So infrequent that we couldn't easily see a pattern leading up to the fault. And after the fault, the amps were all shut down, so the LEDs could tell us nothing (eg encoder, hall etc). Sometimes two weeks of steady use and no faults, then 2 or 3 within a few minutes, then fine again. When the fault happened, we usually lost X position and had to cold start again.

We did all the usual things of swapping amps and axis cards. We even suspected noise on the fault line and added capacitors. Nothing helped. Then a couple months ago we had two faults in a row and so I figured it might happen a 3rd time. So I started the program and ran back to the cabinet. The machine faulted and momentarily showed the encoder LED before going dark. Also noted that in each of the cases, the machine started with a Y move and faulted during it.

About the only thing we hadn't tested (and not easy to test because of how intermittent is was) was the control cable for the X axis. Long story short, the X axis control cable (part number WIR-1107) was worn out and the fine wires within had become fatigued so that at least one of them occasionally lost connectivity. Both the X axis control and power cables run between the Y axis way, part of the way in a drag chain. So even though they are headed to the X axis servo, Y motion imparts movement in the cables. Before we ordered a new cable, with the cable on the bench, we did the tedious work of checking continuity on the 18 connected pins and sure enough, found a wire that lost connectivity with flex on the cable.

Replaced the cable and all has been well since. Moral: don't assume, like we did, that cabling isn't a wear item.