X-axis won't home (occasionally)

Hi there,

New reprapper here

I recently built myself a Prusa Mendel:
- Printed parts from Nophead (very nice)
- 3rd gen. electronics, 5D firmware
- Arcol hotend
- Wade extruder
- optical endstops

I use Skeinforge and Repstrapper.

So far I am getting quite nice print quality (PLA), while learning the ins and outs of Skeinforge.

However...

Occasionally my x-axis starts 'skipping' in the negative direction. Positive direction works fine, so the entire print will start to wander to the right, layer by layer. Luckily, when this happens, it is always in the first layer, so I can quickly stop the print and press Home All.

But the x-axis will still have problems in the negative direction, and instead of Homing, the axis actually 'jogs' a little in the positive direction instead! I have tried lots of things to get the x-axis working again, and usually I succeed within a few minutes (of trying random stuff while swearing loudly):
I have tried switching off the power for the steppers and manually pushing the x-carriage back into the (optical) endstop. With a bit of luck the x-axis will function properly after I apply power to the steppers again.
I have tried resetting the entire setup, rebooting the PC and even re-burning the mainboard firmware (with no changes done).
I have also tried cutting all power and going to bed. Usually this works!

BUT I haven't found any consistency in the 'fixes' I have applied.

Anyway, I was wondering if this problem sounds familiar to any of you experts? Right now I am thinking it may be a loose connection in the endstop cable. The LED on the endstop seems to work as intended (no light while x-carriage is out in the field, and lights up when x-carriage is at Home). But maybe there is some micro noise on the endstop cable that messes with the signal, so the printer sometimes thinks the x-endstop is activated all the time? Can the endstop cables pick up noise from, say, the stepper wires? Any other cable noise that could do this?

I will try and switch the endstop cables for the x- and y-axes tonight, and see if the problem starts occurring for the y-axis instead.

Any hints and ideas will be much appreciated!

-Eriksen, Denmark

maybe you have EMI-problems with long wires or triggering your opto switch by ambient light?

---

Viktor
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Hi Viktor,

Thanks for the answer.

Yeah, I may have some EMI electrical noise problem. My opto cables are made from old HDD ribbon cable. I am not too familiar with noise issues, though. Are there any small cables that would be better shielded (but still commonplace scavenging material)? CAT-5 is a bit more bulky than I would like. I was thinking about the audio cable from CD-ROM drives (between drive and motherboard/soundboard)?

I am pretty sure that ambient light is not the problem. If so, it is very inconsistent. The problem is only with one axis/opto and I haven't encountered any problems when I open the door and let sunshine in, or when I turn the room lights on/off while printing.

-Eriksen

Well, I went over the endstop cable last night and pressed the wires really hard into the plug (a bit like for an RJ45 connector), and things started working.

Here's hoping that the issue is fixed completely.

-Eriksen