Z-Axis problem with router 2600 - please help me diagnose!

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RobWinter
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Z-Axis problem with router 2600 - please help me diagnose!

Post by RobWinter » Thu 18 Feb , 2010 11:08 am

Hi,

We have a router 2600 (about 3 years old with the usb interface). - After a spate of it completly crashing mid program (and casuing the controlling computer to get the 'blue screen of death' the machine has now developed a big issue with the z-axis.

Basically, it won't home or jog correctly. - If you home or jog it (by use of the secret button) it just moves down towards the bed even when you telling it to move away from the bed. - It does this for home or Jog.

- Im fairly technically minded, and have had great support from a chap called Graham at Denford already, but just wanted to run it past some other people and see what they think. - My diagnosis is the controller board from what I have tried below, but please correct me if im wrong.

Fault Finding:
* Checked homeswitch on Z axis - cleared debris and checked continuity - passed - in either case 'fooling the software by taping down the switch prevents any z-axis movement at all confirming the switch and wiring is fine
* Checked all fuses inside the main case with continuity test - all fine.
* Checked it wasnt the Z lock brake by removing temporarily
* On Grahams advice swapped the 'z' and 'x' axis stepper motor connectors round on the main board, and the fault then transferred to the X azis, and the z now worked as it should do - To my mind this elliminates the axis stepper AND the wiring to it, pointing to the controller board ? do people agree?



* Hence my attention turned to the controller board, and knowing a bit about electronics I suspected one of the main driver L298's connected to the heat sink might be at fault (when something needs a heat sink that big....)- Couldnt see any obvious physical signs of damage to any of them, and checked the resistance between different pins on all 3 of them (as 2 of 3 must be working for x and y axis to function fine) - there were no discrepencies in the resistance measures between the 3. - Also checked the big diodes as best I could 'in the board' thought I know this is not a thorough test.

One slightly weird fact is that if you put upward pressure on the 'z' axis while it is going the wrong way it will sometimes reverse direction and go the 'right way' temporarily - both when you swap the conections onto Z or X....

I hear a new board is £300 + delivery, and our school can barely afford that at the moment, so if there is any component I can replace, or any more diagnosis tests I can do on the board before I throw in the towel that people suggest I would be really happy!

thanks,

Rob

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Re: Z-Axis problem with router 2600 - please help me diagnose!

Post by Denford Admin » Thu 18 Feb , 2010 12:37 pm

On Grahams advice swapped the 'z' and 'x' axis stepper motor connectors round on the main board, and the fault then transferred to the X azis, and the z now worked as it should do - To my mind this elliminates the axis stepper AND the wiring to it, pointing to the controller board ? do people agree?
I'd agree with that.

Maybe you've seen this post already :
viewtopic.php?f=54&t=2397

I don't know much about the stepper circuit L297 L298, but maybe its worth replacing those two chips and the diodes (for what they'll cost)
This site has some nice info on this type of stepper driver:
http://reprap.org/bin/view/Main/Stepper ... Driver_1_1
(I don't believe we have a circuit diagram for the Baldor bottom board - so I'll see if I can get one posted in the Electronics section of the forum)

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Steve
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Re: Z-Axis problem with router 2600 - please help me diagnose!

Post by Steve » Thu 18 Feb , 2010 15:50 pm

I agree with everything said.

The way steppers work once they are roatating if you force them to run backwards they will go so (but not as smooth as the correct direction)

I think from what you have described the problem will be with one of the driver chips (the L297 or 298)

I attach a photo showing the devices.

You should be able to buy them from Farnell or RS

If you replace both it should fix it. :D

However if you attempt this and damage the tracks on the board then you will have to buy a replacement rather than get the service exchange as the board would then be unreparable. :cry:


The cost then would be £535 :loads-a-money:
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drive module.jpg
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RobWinter
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Re: Z-Axis problem with router 2600 - please help me diagnose!

Post by RobWinter » Thu 18 Feb , 2010 16:26 pm

Many thanks for the picture Steve, I was wondering which chip belonged to which axis.... I figured it might be those 2, but wasnt sure. - That helps a lot with which ones to take out and change first.

I'm just getting my old man to order the 2 chips on the company account.... Hope it works! - Are the diodes also a potential fault or is this a red hering?

Rob

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Steve
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Re: Z-Axis problem with router 2600 - please help me diagnose!

Post by Steve » Fri 19 Feb , 2010 10:01 am

The diodes could be a problem but I feel it very unlikely. They are there to suppress the back emf from the motor.

The failure of the axis could be down to the control chip rather than the output device as when these fail there is normally smoke and a fuse blows.

If its the output device then this would normally be because either one of the motor windings has shorted to earth (its worth checking the motor wires as they come out of the motor body to see one is not damaged) or that there is not enough heatsink compound behind the output chip and it has overheated.

When you replace the 298 make sure its got plenty of heat sink compound under it and its tight down on the heatsink!

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Re: Z-Axis problem with router 2600 - please help me diagnose!

Post by Denford Admin » Fri 19 Feb , 2010 10:04 am

The failure of the axis could be down to the control chip rather than the output device as when these fail there is normally smoke and a fuse blows.
I think in that case then, I'd be tempted to change the 297 1st and give it a try rather than possibly mess up the heatsink :?:

RobWinter
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Re: Z-Axis problem with router 2600 - please help me diagnose!

Post by RobWinter » Fri 19 Feb , 2010 10:54 am

thanks chaps.

I'll let you know how it goes...... - having real trouble removing either chip from the board to be honest (taking it slow as I dont want to wreck the tracks) - I gather its a triple layer PCB which means theres solder both on the chip side, bottom side and middle..... - real difficut to de-solder - I have all the correct tools, but its a right pig. - The L297's should really have been put in sockets if im honest. - At least the L298's you can cut the legs off and remove 1 leg at a time.

Oh well.... if I wreck the board we'll have to use our newley brought laser cutter to generate things to sell for a 'help the denford' campaign! ..... just as I get one new toy, the other one goes wrong!

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Re: Z-Axis problem with router 2600 - please help me diagnose!

Post by Steve » Fri 19 Feb , 2010 10:59 am

I would change both chips together. If one is damaged then it could pottentially damage the other. You may end up damaging the new parts if you just change one.

The board is just double sided but they are plated through holes. You have to be carefull not to pull the plating out with the device legs.

If you do you need to make sure you resolder the device both top and bottom.

Good Luck!

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Re: Z-Axis problem with router 2600 - please help me diagnose!

Post by Mr Magoo » Fri 19 Feb , 2010 23:28 pm

I've worked on a similar problem where all 3 axes had failed. Turned out the motor connectors had been wired incorrectly so all of the L298s outputs had been shorted to ground :( (with holes blown in the side of them)
Just for info....
- Original symptom: the motors were completely dead (no power)
- swapped out the L298s and the motors now had power on them :D - but still no movement :(
- then swapped the L297s (and socketed them :wink: ) and 2 out of the 3 axes now had movement
- After checking I found I wasn't getting any step & direction input coming into the L297 for one of my axes. I guessed it was the TTL driver chip on the top board, but being surface mount I called it a day and swapped out the top board.
- and all started working.

And yes - the chips were a pig to get out. I ended up cutting the legs of the L297s and pulling them out individually too :?

RobWinter
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Re: Z-Axis problem with router 2600 - please help me diagnose!

Post by RobWinter » Wed 24 Feb , 2010 13:18 pm

Hi again guys,

I swapped out both the L297 and L298 chips on the z-axis. - Unfortunatly, it doesnt seem to have worked... but I have some more concerns now that may help.

I wired it all back together and it did indeed work the first time! - as in I clicked home and it went right where it needed to.... of course I started celebrating then (but too early it turns out!) - I then tried to jog it up and down to check reliability and low and behold the old problem re-appeared..... grrrhh!

- Incidentally, I put my finger on the heatsink connected to the driver chips (the huge junk of aluminium) and it was very hot.... I find this strange seeing as all I did was attempt a home move and try to jog it a couple of times.... hardly a workout!

Does this indicated that something else might be shorting the chips and causing them to blow? - hence why it might have worked once? - or do they always run this hot?

any further suggestions greatly appreciated. - I notice there are some ULN2803 or something similar chips on sockets on the board? - are these worth looking at? - anyone know what they control?

thanks again - keep your ideas coming.... dont really fancy the £530+vat for a new board!

Rob

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Steve
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Re: Z-Axis problem with router 2600 - please help me diagnose!

Post by Steve » Wed 24 Feb , 2010 13:44 pm

Hi,

The 2803 devices are darlington pair output chips.

These are used to drive the step and direction to the L297 device.

It is possible one of these could be faulty.

The attached info covers the I/O parts on the card. The other 2803 will be used to drive the clock and direction.

viewtopic.php?f=54&t=2541

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Re: Z-Axis problem with router 2600 - please help me diagnose!

Post by Denford Admin » Wed 24 Feb , 2010 14:46 pm

They do run very hot.
This might work, and save you replacing any more chips unnecessarily:
If you've socketed the L297, you could try bending Pin17 out of the socket (CW/CCW) and wrapping a wire onto the leg.
You could then switch it manually between 0 or 5V to force the direction yourself...if the problem remains, then you can presume the 2803 is OK

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