After about 4 months of perfect work now big trouble

I made a Prusa I3 box version, I used during about 4 months nonstop, but now I have trouble and I'm out of ideas of where that can come from.
The y axe is making sometime and not at the same height (I really like that could be) an derivation from about 1 or 2 mm sometime more. I checked all stuff on that axe, rebuilt it, changed the GT2 belt but it keep doing it ...
So after that fail, I changed the ramps (never know that can be that who fail, btw I'll change pollu too can be that)
I changed the extrusion temperature, I case of that could be a extrusion blockage resulting by a small move of J-head and make the axe block ( normally I can't have that because in slicer I use the lift option)

This night I changed the tension on Y belt to something really less, that give me an "improvement' but the piece still don't go correctly and result to a movement of about 200-500 micron I think.

If anyone have an idea of what can make that, I'll be happy to test it

belt setup is a GT2 with 20 tooth but as soon as I get the 16 tooth I'll change it. The other change to normal design is I use a 608z bearing (the one with a small metal part on a side) to get the belt blocked on it (maybe I'll test with a 608zz, can be that, but this configuration work perfectly on X axe )

Hope anyone have some better idea then me

Edited 1 time(s). Last edit at 07/29/2014 12:55PM by hoctopusse.

I got lost at the idea of the Y axis changing height and "change a part of the G2 belt".

I changed the Blet, my bad sorry.
I'm on that prob for about 2 weeks.
After posted here I got an idea the only thing I didn't check is the power on step controller, I'm doing a new test print after 10 layers it keep going well, I hope it was just that but I don't get that idea before ... Bad me

Did you not check the stepper driver voltage before replacing the RAMPS? Oops, I see you just did check it. It looks like your Y axis is skipping steps. It could be improper voltage through the driver, your toothed gear on the motor could be loose, or you could have the speed too high in your firmware.

Edited 1 time(s). Last edit at 07/29/2014 10:08PM by AbuMaia.

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MakerFarm 8" Prusa i3v
RAMPS 1.4
0.4mm E3D v6 for 1.75mm

I did that check and I was that not proper voltage
after the change on bearing, I don't know why but it was soo simple then I didn't check. Maybe because the printer runned since long time with that setup and no problem.

Thanks a lot for your reply

For the ramps I have another printer in building so I just switched ramps

Just a thought, but you may have any one of the following issues:
1) Belt issue (inspect for contamination, clean and check belt tension)
2) Motor encoder is dammaged (Swap motor to see if issue changes from X/Y to Z)
3) Bent sticky or dammaged guide rail (clean lube and inspect)
4) Malacious code (reinstall software or try changing to different print design -calibration block etc-)
Good luck.
-Chris