Printer behaving erratically during print from SD

I'm using a CTC printer that I've just built. It mostly runs fine, but every so often will pause in the middle of a print, and home the X or Y-axis (occasionally both together), and then return to the object and start printing. This is mildly annoying and sometimes leaves a bit of string hanging off the edge of the object, but I can cope with that.

More rarely, halfway through a print (usually a longer print) it will just retract all of the filament out of the extruder,
and then carry on with the print - but no longer producing any plastic, so I get a half-finished print.

Both of these effects can occur at random points through printing the same object, so it doesn't seem to be directly related to the gcode. It doesn't seem to be related to retract events either - the last time the filament was ejected was halfway through a large mass of infill.

Does anyone have any ideas what is going on here? I am wondering if it is a glitch in the firmware, but could it be the power supply? I have a 180W LED power supply. (The quality of components is not great - it was a fairly cheap purchase of eBay; I've already had to adjust for the fact that they have used 50k thermistors rather than the standard 100k ones).

I'd be really grateful for any light that could be shed here,

Phil

It doesn't seem to be one problem hat causes these issues.
Homing axis and return to the part to go on printing seems to be related to "minimum layer time". A parameter you can set in your slicer. But then again it would be a regular thing.

Retracting the filament, while it shouldn't could be caused by running hotend/thermistor and stepper wires along each other. ( EMI problems )
It often shows up, with wrong or jumpy thermistor readings, while the heater is in PID mode.

Keep the thermistor wires separate from the power cable and twist the stepper wires, if possible.

Another source of problems could be the 5V regulator on your controller. Check the voltage. if it is below 4.6V, that can cause all sorts of problems.

What version of Marlin are you using? I suggest you try the current RCBugFix branch. It has some SD Memory card stuff tweaked in it.

Thanks all for your suggestions. I don't think it's a cross-talk issue with the stepper motor and thermistor as the thermistor readings are nice and stable. I don't think it's a minimum layer issue as it is really random.

I've started running the machine directly from a raspberry pi using octoprint - and this seems to have eliminated all of the problems I was having, so it seems to be an SD card issue. I'll try flashing the firmware when I've got some more time and I'll see if that fixes the issue with printing from SD.

How can I tell what version firmware I am using? I have limited documentation that came with the printer (it was very cheap)

I know this has been a few months, but I am having the exact same issues. It was suggested that I replace the SD card. I did, and it still does it. I don't have a raspberry pi, and I'm not familiar with octoprint. Did you ever find another solution? My printer is a FolgerTech prusa i3.

I'm having this problem as well.

My printer is a Max Micron dual head prusa i3 clone, which I've heavily upgraded.

At random times the print head will suddenly travel to the X or Y limit, and then return to the print area and continue printing.
Sometimes, even worse, is it will do it in Z!

Imagine being 3/4 of the way through a print and then the hot nozzle suddenly tries to go straight down. CRASH!

For now I've gotten around it by printing via USB/Repetier.

I've re-flashed the firmware with one sent from the manufacturer, but no change.
It's very frustrating because of how random and intermittent it is. I'm very interested in the RCBugFix Marlin but I have no idea about how to implement that.
Do I just copy my configuration.h file into it? I've no idea.

Hope someone can help.

Stephen