[vsystems]

Hi, we got a chinese laser unit 80W at the end of November. Not really sure of the brand since they're barely marked. We had good luck with it up until today when it was powered on, the gantry has a movement problem.
This unit has two speeds for each directly, the "fast" movement and the normal step movement. When you aren't engraving something, and the movement buttons are held down it kicks into fast mode. The unit works fine in all directions in fast mode, but when you press the forward or backward movement button it just vibrates loudly and barely moves or moves with massive resistance. If I power the machine off, I can move the gantry by hand smoothly in all directions. I've cleaned and lubed the linear rails, and checked all the belts and pulleys and everything seems to be solid and tight. I've got no idea what the problem could be.
Any help would be appreciated.
Thank you!
Ron.

[jalessi]

Ron,

Does the machine engrave correctly in all directions?

Jeff...

[vsystems]

We did a test engrave and no, any fine Y axis movements (front to back, I believe that's Y) do not perform correctly, it looks like chicken scratch. It's like the Y axis motor has no torque at all when doing fine step movements, but plenty of torque when it kicks into fast mode. I just finished retensioning all the belts and that didn't solve anything. It's extremely difficult to retension those buggers too, it seems the belt is clamped onto itself and inside each area where the belt is folded is a scrap piece of copper wire. I'm guessing to add thickness to the belt clamp.

Basically, pressing the movement buttons, you can see the motor in the back twitter back and forth as if it was having a difficult time moving the gantry, but if I add a little push along with the button press it moves ok. eventually, if I hold the button down it thinks i'm asking for a long distance movement instead of a step, kicks into fast mode and moves perfectly.
I don't know if it would help to post a video of it in action, I could if it would be of assistance in diagnosing this. I also checked the machine for levelness, it's level, and I can't understand how just last week it was operating fine and today it's all screwed up.

[jalessi]

Ron,

Are you sure nothing is binding?

From what you are describing it sounds like it is missing steps.

A video may help diagnose the problem.

Jeff...

[vsystems]

Jeff,
I've checked every possible angle and point of contact, used a really slick dry film lubricant on the Y axis, and can move it with a small amount of effort when the machine is off, the exact same amount of effort it requires to move the laser head left and right, so I can't fathom what it could be binding on. I've never had any CNC machines other than this one, so I'm stumped, and the chinese manufacturers are no help since they've just told me to clean/oil it and "it be good again"
I've dealt with linear rails on a printer before, so I know they're good and solid, but since the machine is hardly used, I can't figure out what the heck happened between now and last week when it worked perfectly. Last thing I cut in it was styrofoam, and although I've never cut styrofoam, I'm sure it didn't destroy the gantry. Another strange thing I noticed today is the Z axis for the table is moving unbelievably smoothly, before it used to rattle and make a hell of a noise, now it's smooth as butter. Honestly I wish that was rattling again if it would fix the main part.

I've uploaded a video to youtube here.
[ame="http://www.youtube.com/watch?v=dIRROtfjaXw"]YouTube- video-2009-12-28-19-43-50[/ame]
The sound appears to be out of sync... I hate youtube.

The HQ mode is much clearer in quality too.

and as far as I can see by watching it, it's not missing any steps unless the motor, internally, has something broken inside it like a broken tooth that I can't see...

[jalessi]

Ron,

Is Mach3 controlling the laser?

Do you have a instant messenger?

My yahoo id is: jeffalessi

Jeff...

[vsystems]

Jeff,
I'm not in the know enough to know mach3, I've heard of it, but don't know what it is. And in any case... I found the problem. I started pulling screws out and low and behold, the stepper motor without ANY load and without any belt on it behaves the exact same way as the gantry was moving. So.. the million dollar question is, is it possible to replace this without the help of the manufacturer?
I'l post more info on it soon as I pull out the remaining screws.

[Rob West]

Hi
On my Chinese laser the steppers are the same on both axis.
Can you swap the waring or the steeper controllers to see if the problem moves to the other axis? (only do this if you are electrically minded).
It sounds to me as if the FET’s or similar are not firing correctly on that motor controller.
Cheers Rob

[vsystems]

I'm electricallyt minded, not so much for electronics though, so I pulled the motor out completely had to cut wires in order to do so because they fed the wire through a small metal hole, under the laser tube and then put it through another hold and attached a socket style end to it that won't fit through either hole.. honestly why put a socket on it if it can't be pulled straight out. I can put that back together if necessary, but anyway, now I think the issue may be electronic since the stepper seems to move smoothly in my hand the only markings are JigoCheng, DC 5.2v... then a big hole where some of the label was torn away. Type 57BYGH350B-YH.
I have a bench power supply I'm going to attempt to put 5.2v into it and see if it jiggles or anything.

Does the motor itself have a reversing gear (in case of a jam) or is that the electronics that reverse the motor?

Correction the label says "DC 5.2" the A or V is cut off, so I don't know if it's 12v and 5.2A or 5.2V?

[jalessi]

Ron,

Most likely the stepper motor is good.

The stepper driver is most likely the culprit.

Do not try and run the motor with a power supply.

I suggest you stop experimenting unless you want to cause more damage.

Guessing is going to get you in trouble.

Jeff...

[jalessi]

Ron,

Follow the wires from the stepper motor to where they terminate and take a picture of the control "stepper drive"

That way we can identify it and suggest a vendor to order a replacement.

Jeff...

[vsystems]

Okay, closing in on the problem here.
I'm gonna put the motor back in.
I switched sockets for the stepper motors, and then the X axis started acting the same way, switched them back and X is good again, Y is bad. So yes, the driver is bad. Does this happen often?

So I'm gonna send a few pictures here, If someone would be so kind as to point out what I'll need to look into replacing to get this working again, since I can't tell what's plugged into what, I'm assuming the twin boxes are for the steppers? The wiring is so precise and neat in this unit it's actually making it difficult to troubleshoot.

So if anyone could assist me, again, I'm very very grateful.

[jalessi]

DO NOT CONNECT OR DISCONNECT THE MOTORS WITH THE POWER ON YOU WILL BLOW OUT THE DRIVERS

[vsystems]

DO NOT CONNECT OR DISCONNECT THE MOTORS WITH THE POWER ON YOU WILL BLOW OUT THE DRIVERS

I appreciate the concern, but I took all the necessary precautions. Powered down inbetween switches. The pictures are dark, I've got to leave work now, but I'll be back in at 10AM, if more info is needed, I can post again then.
Thank you Jeff and Rob.


Here are the pictures of the insides.

[zax15uk]

Sorry I'm coming in late here, the problem is very common.

Your driver isn't providing power to one of the windings so when trying to step slowly it just jumps back and forth, sometimes stepping past the coil that isn't on. When stepping faster it builds up enough momentum to 'jump' past the unenergized coil.

The same symptom can be caused by a bad motor coil, but you've correctly diagnosed it to the driver.

It may be possible to replace the driver IC, maybe a L297 on your machine (not positive). Usually mounted on the rear of the board using the back panel as a heatsink.

Zax.

[jalessi]

Ron,

Does the stepper driver have a number on it like " MD556"

Jeff...

[jalessi]

Ron,

I believe your machine is fitted with 3-phase stepper motors and stepper drives, they are not run of the mill parts.

Jeff...

[Rob West]

Hi Ron
It looks like Jeff and Zax have the info you need.
Unlikely I am not down at my workshop so cant look at the steeper drivers, but looking at your other photos it is different to my IE1200 in wiring detail.
All the best and thanks Jeff and Zax
Cheers Rob

[zax15uk]

Ron,

I believe your machine is fitted with 3-phase stepper motors and stepper drives, they are not run of the mill parts.

Jeff...

Jeff,

I think you're right as the picture shows 3 wires for each axis.

That's an unusual arrangement for steppers, probably using SLA6023 or SLA7611M drivers. They're going to be hard to find compared to L297/8's etc.

Zax.

[vsystems]

Well, that's not encouraging... The motors each have 6 wires, and I'm assuming the driver units are those two identical looking boxes. After closer inspection, the only markings I can discern are:
SH-30806N.

The motors have 6 wires, it seems only 4 or 5 are connected to anything, it's difficult to tell without testing continuity on all the wires, but not possible now that i reassembled everything.
Only 4 wires plug into the top of each of the driver? boxes. and power in the other wiring block below that. I'm going to try to trace the correct one and remove it to have a look inside.