Troubleshooting Comet

A place to talk about anything that doesn't fit anywhere else.
Canadian_Comet
Posts: 15
Joined: Fri Dec 04, 2015 12:37 pm

Re: Troubleshooting Comet

Postby Canadian_Comet » Fri Dec 04, 2015 7:00 pm

WOW That was not fun, definitely something on the PCB causing a short, replaced the LM317 regulator and got about 1V ( instead of 5V ) before it popped about 15 seconds into power up. And yes that literally what happened, it popped like popcorn ( allways wear safety glasses when testing unknown issues in a power supply :lol: )

Oh well, was worth a shot, but now I'm concerned that one of the other PCB may be shot ( example a motor driver ) which in return caused the break out board issue.

I should have disconnected all the drivers before testing, that would have isolated the problem.

Crap on a stick....... looks like I'm not getting this thing running this weekend :cry:

Canadian_Comet
Posts: 15
Joined: Fri Dec 04, 2015 12:37 pm

Re: Troubleshooting Comet

Postby Canadian_Comet » Fri Dec 04, 2015 7:36 pm

Very interesting, I removed the power to the breakout board and the damaged regulator to troubleshoot what is causing the short on the 5V supply.

I measured 2.6 ohms between the +5V and GND which would indicated a required current of 1.9A at 5V

The regulator is rated for 1.5A min ( 2.2A typical ) when the Vin-Vout is less than 15V
The regulator is only rated for 0.4A when Vin-Vout is 40V

Our Vin is 40V from the big supply and Vout is 5V so the differencial is 35V

At 35V the LM317 package is on rated for about 0.5A


Given what the four driver boards are loading the breakout board at, it's no wonder why my new LM317 regulator exploded after startup.


With everything disconnected I see 23 ohms between +5V and GND

With just the A-Axis Probostep connected the resistance is 5.0 ohms
With just the Z-Axis Probostep connected the resistance is 6.7 ohms
With just the Y-Axis Probostep connected the resistance is 7.1 ohms
With just the X-Axis Probostep connected the resistance is 7.6 ohms

If you do the math with the above numbers the load should be around 1.5 ohms instead of the 2.6 ohms I measured with everything connected.

Canadian_Comet
Posts: 15
Joined: Fri Dec 04, 2015 12:37 pm

Re: Troubleshooting Comet

Postby Canadian_Comet » Fri Dec 04, 2015 7:43 pm

Long story short, I do not know what to do next, I wouldn't think that it's normal for the Probostep UX Rev1 motor drivers to load down the breakout board like this, given they each have their own fused 40V supply I would have thought it would have been just simple logic circuits, which should not load down the circuit.

Not sure, but perhaps when the original LM317 crapped out it might have sent a spike of higher voltage ( 40V ) to all the logic components killing every single thing attached to the breakout board.


Anyone else out there with lots of electronics knowledge and ability to measure your current requirements for the breakout board?

I'd hate to buy a new PBX-RF breakout only for it to be damaged due to four damaged Probostep UX boards.

I emailed Probotix to see the availability of new Probostep motor drive boards, don't see them on their website anywhere.

beltramidave
Posts: 214
Joined: Fri Aug 21, 2015 8:54 pm

Re: Troubleshooting Comet

Postby beltramidave » Fri Dec 04, 2015 7:57 pm

They are using the Mondo drivers now.

http://www.probotix.com/CNC-CONTROL-SYS ... tor-Driver

One thing I remember Len saying is to definitely do not unplug the steppers with the controller powered up. I may be able to take some measurements on my machine if you tell me exactly what you want.

Dave

beltramidave
Posts: 214
Joined: Fri Aug 21, 2015 8:54 pm

Re: Troubleshooting Comet

Postby beltramidave » Sat Dec 05, 2015 6:14 am


Canadian_Comet
Posts: 15
Joined: Fri Dec 04, 2015 12:37 pm

Re: Troubleshooting Comet

Postby Canadian_Comet » Mon Dec 07, 2015 10:40 am

Thanks for that information, based on the data sheet I think all of the probostep drivers are likely damaged, I'm fairly certain that all the logic circuits were hit with a voltage spike the logic circuits could not handle ( example 40V instead of 5V )

The SLA requires 3.3 min to 5.5V max Vdd ( logic supply voltage) with a spike of no more than +/-0.5V

I have to assume my thoughts about a 40V spike due to logic power supply failure are likely correct.

Probotix should have put an isolated DC/DC converter to reduce the 40V to 5V, then the regulator would not be required at all.

If I remember correctly MeanWell had a DC/DC that was rated for 36-72V input and 5V output at a reasonable power, I think it was a about $15.00

The LM317 regulator used on the breakout board is not efficient, it is converting 35V out of the 40V supply at a given current into heat

As well there was no heatsink compound on the LM317 which derates it's capabilities significantly, over time the contact surface will corrode and the heatsink will become useless.

So probably like 10% efficiency for supply current, where as a DC/DC will be in the range of 75% to 95% depending on several factors because it is transforming the power down to a lower value instead of converting excess voltage into heat.


Oh well, seems I am screwed because of a simple power supply issue. This is going to cost me thousands in downtime, likely more than the cost of a brand new unit, as I needed to have my prototype case done by today and all I have is a chunk of MDF sitting on the Comet.

Stuff happens, it's been a good little unit, nothing I can do about it now but I'm certainly going to yank apart the replacement and modify the logic supply to be more robust.

And yes, I manufacture electronics for a living, just not familiar with CNC stuff at all, first time I've popped open this system or any other.

beltramidave
Posts: 214
Joined: Fri Aug 21, 2015 8:54 pm

Re: Troubleshooting Comet

Postby beltramidave » Mon Dec 07, 2015 10:46 am


Canadian_Comet
Posts: 15
Joined: Fri Dec 04, 2015 12:37 pm

Re: Troubleshooting Comet

Postby Canadian_Comet » Mon Dec 07, 2015 2:36 pm

Yes, I have an inquiry on that unit, I wanted to know if it's a "plug and play" replacement for my old unit.

The old Controller has four axis ( XYZA ) where as the new one has five Axis so I was curious if I need to reconfigure things in software or rewire things with respect to connectors.

Mainly I wasn't sure as to whether you take the old "A" and plug it into "Y2" or continue as it was and plug in the second Y motor back into the A port.

No response yet, hopefully they get back to me soon as I need to make a decision on what to do with this guy. I have been thinking of getting a much larger more expensive unit with more features, but the Comet is great for making prototypes and it's easy to hide away when not in use.

beltramidave
Posts: 214
Joined: Fri Aug 21, 2015 8:54 pm

Re: Troubleshooting Comet

Postby beltramidave » Mon Dec 07, 2015 3:15 pm

These are not quite plug and play replacements for the older controllers. The motors need to be rewired!! There are pigtail connections at each motor (under heat shrink) that need to be taken apart and reconnected for bi-polar.

I know this as Len helped in replacing several of our controllers with the new controllers. It was not hard to do, just takes a little time...and some heat shrink tubing to put back together.

As far as the Y2 connector, you are correct. You will not use the Z connector (but I do think it is wired to a driver, so you have a spare).

I would recommend talking to Len or someone at Probotix to verify, but I am 99.9% sure on all of this.

http://www.probotix.com/wiki/index.php/MondoStep_4.2#Wiring_to_Motor

Canadian_Comet
Posts: 15
Joined: Fri Dec 04, 2015 12:37 pm

Re: Troubleshooting Comet

Postby Canadian_Comet » Tue Dec 08, 2015 4:42 pm

Was just posting this and I received a response from Probotix, they gave me this link for the conversion:

http://www.probotix.com/wiki/index.php/ ... Conversion

It seems odd to leave the Z Axis, I would have assumed X, Y1, Y2, Z and your saying its X,Y1,Y2,A ?

What do you do with the extra axis, do you just leave it unconnected, or do you have to pull apart the controller and disable the last driver?


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