MESA 7i76E burning out issue

Perhaps an output is marginal because of previous damage

I would verify full 5V swing on all step/dir pins.

Here is a simple script to toggle all stepgen step and direction pins slowly:

 


Download then

chmod +x stepgens.txt

and

./stepgens.txt to run

Note that this needs a relatively recent mesaflash

github.com/LinuxCNC/mesaflash

Thanks a lot for your help!

Now that I hooked up an oscilloscope, the problem disappeared completely again - can't reproduce it anymore, at all.

That made generating pulses easier of course, I simply jogged the thing along. The levels of the step+/- pins on the motor side are around 4.8 volts, and -4.8 on a pulse.

I also noticed that the level between STEP- and the cable shield (GND) is around 40 volts AC (50 Hz). I can't say I understand why that would be so. Is that normal/intended?

Ack!! 40V is a real issue and indicates a grounding problem. This likely
what damaged the step/dir outputs (accidental contact to shield ground would do it)

I would verify that the drive frame grounds connect to earth ground and that the
7I76E ground (24V logic power ground) is also connected to earth ground.

Ah-ha! The 24V field power GND is not connected to earth ground, I was not sure that it should be. That probably explains it then.

Just weird that the machine ran fine for so long.

Thanks, I was getting frustrated with the constantly changing symptoms. I will connect those grounds tomorrow and test again.

So, change made, AC power component is gone and first small test job ran successfully. Hoping for the best . Thank you again!

I finally found the real cause.

Today i got the amplifier fault on another joint (joint 0) and I found that it the problem happened whenever I turned on the spindle.

After several attempts to measure the ground connections the machine stopped in a position where I found the machine frame was not grounded.

The reason: The spindle connector got loose. The machine frame was grounded through the spindle cable, and that cable had become loose.

All I had to do was tighten the screw of the connector. Ground connection works reliably again and the machine runs well. Phew.