All in 1 DC #412 Decoder diff error

[CJD]

I will apologize now. I installed this unit on an old Bridgeport. Although I did the entire install, I do not remember much. It has operated flawlessly, until today, when it started the day with an MPG1 encoder error, and a Z axis #3 Encoder Differential Error.

After 5 hours, I got the MPG error to go away by removing it in the 348 parameter by setting 0. I have never had an MPG 1, so no idea why all of a sudden this was an issue. The parameter was set to 15 before I changed it to 0.

But, the Z axis encoder dif fault will not go away. I checked all connections, and the encoder works properly when I manually spin the motor. I opened up the encoder, but all looks well on the inside, with all connectors checking 0 ohms on both sides. The system is blocking the main E-Stop relay at both H6 E-Stop relay AND the One Axis DC-1 Drive Fault Relays.

Any ideas on where to go from here would be appreciated.

[CJD]

Well, I finally found the manual I needed with all the parameter settings...CNC Mill Manual. By setting Parameter 332 to 255 I managed to suppress the error and all works. That seems to lead the diagnoses to noise on the Z axis encoder. I realize this is only a work around and would love to hear any ideas to fix the noise issue.

I have a distant memory of having many axis encoder faults during the setup 5 years ago...but I have no memory of how I dealt with them?!? The only thing new in the garage is an EV car charger, but it's at least 10 feet from any of the mill systems. Maybe it'll go away like it showed up...

Oh...one more question. The Z axis is the axis 3. Could someone give me the number to set in parameter 332 to disable only axis 3? 255 disables all axis encoder faults.

[cncsnw]

It is more likely that you have a faulty connection in one of the A, /A, B or /B leads from the encoder; or you have a faulty encoder.

Often, an encoder that is only talking on one of the two differential wires will still show reasonably accurate counts (though if you run it long enough and fast enough, you will probably find that it loses position).

You could check for correct differential signals with a DE9 breakout and pass-through. You could even build the whole test fixture shown here:
http://www.cncsnw.com/EncoderTest.htm

You could isolate the problem to a faulty encoder vs. faulty cable/connection by swapping motors with another axis (while leaving all cables in place, of course).

[CJD]

I am very impressed! As I read the explanation, I realized I have an entire battery of oscilloscopes that can easily accomplish the same thing. You are very helpful in steering me to the right direction and labelling the pinouts, so I know where to look...thank you!

I also agree with your thought that the encoder is likely the issue. I have followed the wiring many times, and there are no anomalies with the wires.

Yesterday I thought I had the machine workable. It turns out it works in manual modes...but the encoder fault trips off any CNC jobs.

I'll update when I find the culprit...thanks again

[CJD]

That was easier than I thought. I found an old post from years ago where I had the encoder error on axis 4. It was dirt that caused that. Sure enough, I popped the cap on the encoder and all connectors and doused everything with contact cleaner. It's working!

I have to assume a couple things about these encoders:

1) They do not like sitting for many months between usage.
2) Even with all the seals, the hot, oily, chip heavy environment gradually introduces oil and debris into the sealed encoder components.
3) Aside from dirt or misuse, the encoders are very, very durable. I am pretty sure mine are over 40 years old and on their 3rd system driving them.

Thanks again SNW