I'm back and I receive he ramps 1.4, cable it and test it.
I only have one thing to say: WONDERFULL!!!!
I have no more shifting and my printing quality has increase (much less delamination and cleaner quality).
I really recommand to switch to ramps 1.4 (instead of melzi board).

I'll inform you!!!

the difference ? hmmmm 60 euros ? joke ;P

looke here : 
arduino mega2560+ramps 1.4+ 5pcs A4988 Stepper Driver Module ...  24 euros shipping include to france

ok, you need to wait something between 1 to 3 weeks for delivered...

the only difference i found between a Chinese clone of ramps 1.4 and other is sometimes the power drivers of the hot bed that can't support heavy current... but the the pangu i3 bed current is not very hight... so no problem... and at this price, you can even take a second one for spare purpose... i already buy an extruder from this vendor without any problems ( shop : http://www.aliexpress.com/store/210094 ) ... if you didn't know Ali systeme, its'like a chinese amazon with a size of amazon+ebay together...

for the method, yep...  you can even try to use the temp ramp number 1 from standard firmware .. it's the one that is used in the original pangu sprinter firmware...

you can also add the the temp ramp i made and extract them from the marlin firmware...

but i think you can also use my marlin firmware for pangu i3 with ramps board, you just need to change only the board type in the firmware and that's it ...

I thought about replacing the A4988 but it's not possible.
The melzi board has too much thermal problems and as it's impossible to replace the drivers, I'm really thinking about replacing this board with a ramps 1.4.

After having a look on internet, I saw many board at many prices (arduino + 5 drivers+ramps board: price from 40 to 100€).
I wonder:
- What are the differences between a 40€ ramps 1.4 and a 100€ ramps 1.4?
- Do you see any better board (for approximatly the same price)?
- @YSB: I thought about taking a SW for a prusa I3 adapted for ramps and just take over the bed and the hotend temperature curves. Is it the right methode?

Many thanks in advence for the help.

that's why i never touched this damn drivers... the last test is to connect one of your "dead" stepper to the z axis and try to move it... if it move, you are good to change your card...

so the results of my test is that I made NO TESTS.
in fact, when I started it, X and Y axis doesn't move anymore so I set reference voltages of each driver to their previous values but nothing changed.
I have connected an other stepper to the X axis and nothing happened.
Conclusion: X and Y axis drivers are out of order. I may have destoyed them when changing the reference voltages... And on the melzi board, it is not possible the replace them :-(

Do you share my conclusions?

many thanks for you answer.
My belts are tighten enough and I already got the fan blowing on the melzi (from previous discusions we had).
But my steppers were untuned. I untuned them to reduce the printer noise but tjis can be the root cause.
So I set every voltage to 1.45V.

I'll make a test tomorrow and let you know.

the common case are :
belts are not tighten enough , so the motor skip  steps... in the case of the pangu i3, it can be the belt under the bed OR  the belt between the two side carriages and the extruder carriage...

solution : double check your belts , do not overtight them, but well enough...

the stepper driver are too hot
solution : put a fan (on the top) that blow on the melzi  toward the bottom ...

perhaps it's a problem of current of the stepper driver... (search for fine tune current - this video is for a printboard that is the same type http://www.youtube.com/watch?feature=pl … PU0vL-VQl0 )

I have a pangu I3 printer (based on a prusa I3).
You can find some descritions in the below threads:

http://www.soliforum.com/topic/5436/pangu-i3-the-best-price-quality-ratio/

http://www.soliforum.com/topic/5755/pangu-i3/

As you can see in the below picture, I get a shifting in X and Y axis.
This is not due to too low belt tension because each axis has a belt tensioner and after the print, belts tensions are OK.

I'm thinking of two possibilities:
1) A thermal shutdown of the electronic board (mine is a melzi board) that cause some steps loosing.
2) A too temperature of the stepper motor.

Does any one of you had already this problem or can help me?

Many thanks in advance.