Unresolved Y axis fail

I had a print running today that was going perfectly, and when I got back it was almost finished, but the Y axis had jumped in the +Y direction about an inch. I can't be sure, but it looks that it may have initially jumped more than that, and then jumped back to the 1 inch offset.

Needless to say, the print was ruined.

What would cause this?

The printer was running alone in a room, nobody bothered it, the cat is locked out.
The print was still solidly attached to the glass, so it didn't slip.

 

Have you checked the y-axis belt tension? It may be slipping on the pulley. I had a similar problem a while ago with the x-axis on my printer than was fixed by tightening the belt.

 

Hmm.. Ok, No I've not checked this. Is there a howto somewhere? I've never had the machine open that far yet.

I see how the deck comes off, but the heater wiring does not appear to have a connector to facilitate removing the plate.

 

lift up the glass and give the belt a flick. It should be relatively tight, but not too tight

There's a screw on the front and back Y brackets that you can use to tension the belt a bit more

 

and if tensioner already bottomed out... just remove belt, cinch up a tooth or 2 and re-attach.

 

One issue I had after mucking around under the bed was the new heater ribbon cable was not perfectly clamped up to the back of the y-axis carriage. Enough of the cable hung down that it would catch on the thick black piece of plastic that almost everything mounts to .

 

I see now. The one in the front is maxed out, but the back one still has range.
I put a couple turns on it, and we'll see what happens.

Thanks!

 

Could you show a picture of what you going to put a couple of turns on.

 

if you look at front or back of your platform (below the glass), there's a screw on the port side. (in the brace that connects the sliding rods) Think its the only one screw there. the belt attaches to a plastic holder on the other side. you can't miss it. follow your belt.