Steppers only work intermittently if I jog two directions at once

09 Apr 2017 22:45 #91101 by Michael
I was attempting to add a simple tachometer today. It is a photo interrupter and I tested it and it worked fine. I was running it off 5v power from my mesa 7i76 and it was inputting into A+. I also added a volt/amp meter (crappy ebay one) on the same 5v and gnd. I installed it and tied the cable to the spindle motor cable. Everything looked good until I turned on AC power to the motor controller and got the pop of a short circuit. The screen went dead on the volt/amp meter and I shut down the power. I pulled the cables all apart to see if I could get power back. While I get 5v power off the 7i76 and all my LEDS on the board and stepper drivers indicate all is well but.....

When I attempt to jog any axis I get nothing. If I attempt to jog 2 axis at the same time I will get intermittent activity from both but it is jerky and a quarter turn at best of the lead screw. Any thoughts on where to get started with the diagnosis would be great. I don't care about the tach or the meter, they were all after thoughts anyways.

Here is what I know:
Stepper power supply is fine
When I jog an axis the voltage on pul+ to pul- goes from .6v to 1v in one direction and .6 to .8v on the other
When I jog an axis the voltage on dir+ to dir- goes from .6v to 1v in only one direction
I have 5v power off the original pin I was using for the tach
The limit switches all work fine also the E stop

I am going to continue to dig around but would appreciate any advice pointing in a more specific direction.

Thank you
10 Apr 2017 12:01 #91112 by tommylight
The voltage on +dir and -dir should go from -10V to +10V, so start by checking the voltage regulator for step and dir outputs. It looks like it is way below what it is soposed to be, but still functional.
PCW is the MAN regarding Mesa boards, so you should first check with him before atempting anything.
13 Apr 2017 13:31 #91304 by andypugh

tommylight wrote: The voltage on +dir and -dir should go from -10V to +10V

I think 7i76 is 5V on step/dir (but I have never measured it)

It might be interesting to measure the step/dir voltages at the DB25 connector, as those signals are direct from the 5i25 and are only buffered by the 7i76.
13 Apr 2017 13:48 - 13 Apr 2017 13:48 #91309 by Michael
Just so I follow correctly. I want to measure pins on the db25 of the 5i25. And I am referencing direction pins 1-5 and step pins 6, 14-17 to any one of the ground pins 18-21?

And pins on the female 25 read right to left correct?
Last edit: 13 Apr 2017 13:48 by Michael.
13 Apr 2017 13:50 #91310 by andypugh
If you look very carefully there are numbers inside the connector next to the pins.
14 Apr 2017 01:32 #91337 by Michael
Too small for my eyes to tell that was there. Linux CNC would not boot without that 7i76 (which was out for repair) so I never got around to testing this. Fortunately the 7i76 came back this afternoon from Mesa repaired. They replaced 74ACT540 and ISL32273 and now everything works. Thank you for all the help and suggestions.
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