Strange problem

I have a friend that does not have an Internet connection, so I am searching for him about his problem.
Although I have a similar machine that is using RAMPS, I have not come across this particular condition.
Everything seems to be working as it should, prints very nicely and then all of a sudden the Y axis will make a noise and skip some steps.
It sounded like the belt slipped, but after checking and rechecking several times, ruled out the belt slip.
The gear is firmly attached to the motor shaft, belts are tight and in good condition, no obstructions in the way, nothing sitting on the belt to cause a jump.
Checked the motor terminals, and all seem to be well connected.
Checked the stepper driver voltage and that is as it should be.
Checked the rods and even replaced the linear bearings in case that was the problem.
The bed moves back and forth very easily and smooth.
One thing that was noticed, the jump always happens when the Y axis is changing direction, it doesn't happen when moving forward or backwards.

He has asked for my help, but I am unable to resolve the problem, we have checked everything we can think of and replaced several parts that may have been suspect, the problem still persists and can happen at any time during a print. We have even sliced the files on different computers using different settings in case it was a slicing problem (didn't think it would be, but)

Has anyone any suggestions to what we might try next??

Thanks

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[regpye.com.au]
"Experience is the mother of all knowledge." --Leonardo da Vinci

Have you tried to lower the acceleration values on th Y-axis?

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enif
Have you tried to lower the acceleration values on th Y-axis?

#define DEFAULT_MAX_FEEDRATE {500, 500, 2.5, 25} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {500,500,50,750} // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot.

#define DEFAULT_ACCELERATION 500 // X, Y, Z and E max acceleration in mm/s^2 for printing moves
#define DEFAULT_RETRACT_ACCELERATION 2000 // X, Y, Z and E max acceleration in mm/s^2 for retracts

// Offset of the extruders (uncomment if using more than one and relying on firmware to position when changing).
// The offset has to be X=0, Y=0 for the extruder 0 hotend (default extruder).
// For the other hotends it is their distance from the extruder 0 hotend.
// #define EXTRUDER_OFFSET_X {0.0, 20.00} // (in mm) for each extruder, offset of the hotend on the X axis
// #define EXTRUDER_OFFSET_Y {0.0, 5.00} // (in mm) for each extruder, offset of the hotend on the Y axis

// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
#define DEFAULT_XYJERK 15.0 // (mm/sec)
#define DEFAULT_ZJERK 0.4 // (mm/sec)
#define DEFAULT_EJERK 5.0 // (mm/sec)

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[regpye.com.au]
"Experience is the mother of all knowledge." --Leonardo da Vinci

OK, we tried messing around with the settings and reduced the jerk down to a really low setting and the problem is still there. (just added more problems now)
Can't seem to find what is causing this issue.

The printer is working in every way well, except after a few layers the axis misses steps (or what looks like it misses steps) The part that is being printed will be out of position along one axis and that messes up the whole print.
This can happen again and again if the print is left to finish, forming steps in the print, all in the same direction.
This guy has come to me for help, but so far I have not been able to help him at all and just look like a fool because it is a problem that I have not encountered before.

I have checked the physical movement of the bed, and all is good. Changed the linear bearings for new ones, checked the reference voltage on the stepper motors, checked the belts for being too loose or too tight, changed the plug end for the stepper motor, adjusted the jerk settings and tried many variations, but still can't find the problem.

Anyone have any ideas to try that I haven't thought of????

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[regpye.com.au]
"Experience is the mother of all knowledge." --Leonardo da Vinci

This seems really to be a difficult one!

So just some "far-off" ideas...

- check that the Y-belt is well centered and aligned (no rotational force when pulled by belt)

- exchanging the X- and Y-motor to see if the problem is motor related

- exchanging the X- and Y-stepper drivers to see if the problem is stepstick related

- reducing the baud rate to ensure that it's not a (strange!) communication problem

- double check the Y endstop (wrong trigger due to some mechanical vibration?)

- detach the controller from the printer frame, so that the Y-carriage movement does not cause vibrations in PCB (cold solder joints?)

I know, none of these are probable causes - but since you checked everything else...

Good luck!

Checked the belts first thing, also swapped motors around and also changed the stepper controllers too. The board is off the machine while setting up.
Endstops are all working correctly.
Haven't changed the baud rate as we are printing directly from an SD card.
Prints fine and then it goes and jumps position at random.
Rewired the motors too, just to make sure it wasn't a bad connection.

Got me beat.

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[regpye.com.au]
"Experience is the mother of all knowledge." --Leonardo da Vinci

If you swap the entire electronics (Mega+Ramps) with the one of your own printer ... does the problem move with the electronics or stay with the printer?

Quote
enif
If you swap the entire electronics (Mega+Ramps) with the one of your own printer ... does the problem move with the electronics or stay with the printer?

I guess that is the next try. Thanks for the idea.

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[regpye.com.au]
"Experience is the mother of all knowledge." --Leonardo da Vinci

Quote
regpye

Quote
enif
If you swap the entire electronics (Mega+Ramps) with the one of your own printer ... does the problem move with the electronics or stay with the printer?

I guess that is the next try. Thanks for the idea.

I swapped over my electronics to his machine and managed to do a 12 hour print without any issues. It printed over night and didn't do what his machine was doing, so it must be something in the electrionics system somewhere. Now I have to get my electronics back again ha..ha..

I guess it will need to be a trial and error fix, test different parts to see if it happens say with the RAMPS changed or the Mega changed, or the stepper drivers changed. Can't think of anything else to try. Makes it hard because it is so random.

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[regpye.com.au]
"Experience is the mother of all knowledge." --Leonardo da Vinci

Well, at least you now ruled out any mechanical problem in the printer itself...

Were you running the tests with your original firmware or have you tested with the "cloned" firmware from the faulty controller?

Quote
enif
Well, at least you now ruled out any mechanical problem in the printer itself...

Were you running the tests with your original firmware or have you tested with the "cloned" firmware from the faulty controller?

We found the problem and it is very simple, so maybe others can get caught with this one.

The electronics has a cooling fan and his fan was mounted backwards so that it didn't blow over the stepper drivers.
One of the drivers must have been getting too hot and was shutting down for a few milliseconds and causing the lost steps.
When the problem was noticed, and the fan turned over, the problem went away.

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[regpye.com.au]
"Experience is the mother of all knowledge." --Leonardo da Vinci