Tandem X axis won't move

Yes weird - after the 'show" then it worked

during movement each reads at 7.5V when still 3.5V

7.5V is not really possible unless something is really broken

Please measure across the STEP0+ and STEP0- pins in both states of the invert parameter
and show the polarity. This will verify that the STEP0 signal is getting to the output pins and that
the output drivers ( + and - ) are OK

edit: (measure when not moving)

Yes the Voltage should be 5V from the computer, but that is not what it shows on 2 digital voltmeters
(I HATE digital meters) 7.5 was micro-volts which is a small mv is a corner of the display.

so here we go (rounded to x,x
still running
00 pul+ to pul- 0.3 3.5
00 dir+ to dir- 3.7 3.5

01 pul+ to pul- 3.5 3.5
01 dir+ to dir- 0.7 0.7

I really cant make any sense out of those numbers, are you measuring them at the 7I76?
Are you changing the polarity of stepgen 00 and 01 step and direction with the halcmd?
if you are only changing the stepgen 00 step polarity, only the top line should change (and it does)
but the voltages between the 7I76 STEP+ and STEP- should never be close to 0
(always greater than 3V absolute and + or - polarity depending on the output polarity setting)

halcmd setp hm2_5i25.0.stepgen.00.invert_output FALSE 4.5V
halcmd setp hm2_5i25.0.stepgen.01.invert_output FALSE 3.5V

halcmd setp hm2_5i25.0.stepgen.00.invert_output TRUE 0.7V
halcmd setp hm2_5i25.0.stepgen.01.invert_output TRUE 3.4V

do you mean that stepgen01 show +3.5 and -3.4 (or vice versa)
Since Stepgen 01 is working having it not change would be odd

Getting a difference of only .7V across STEP0+ and STEP0- at the 7I76 and when its not moving
indicates a bad output.

Machine with MDI motion in X

halcmd setp hm2_5i25.0.stepgen.00.invert_output FALSE 4.5V
halcmd setp hm2_5i25.0.stepgen.01.invert_output FALSE 3.5V

halcmd setp hm2_5i25.0.stepgen.00.invert_output TRUE 0.7V
halcmd setp hm2_5i25.0.stepgen.01.invert_output TRUE 3.4V

Machine with NO Motion
halcmd setp hm2_5i25.0.stepgen.00.invert_output FALSE 0.0V
halcmd setp hm2_5i25.0.stepgen.01.invert_output FALSE 3.5V

halcmd setp hm2_5i25.0.stepgen.00.invert_output TRUE 0.0V
halcmd setp hm2_5i25.0.stepgen.01.invert_output TRUE 3.5V

OK I'm having real trouble interpreting what's happening here...

1. You are not stating the polarity of the readings
2. Are the readings at the 7I76 and _across_ the STEP0+ and STEP0- pins?
3. There is no such parameter as hm2_5i25.0.stepgen.NN.invert_output
(there are parameters hm2_5i25.0.stepgen.NN.step.invert_output and hm2_5i25.0.stepgen.NN.direction.invert_output )

1) will change below (Again I HATE digital meters)
2) yes I am reading from the screw posts of the 7i76
3) I inadvertently dropped the .step when copying the address. Sorry for confusing you.

I have run this through completely 4 times to check my numbers. I am totally surprised how 8 numbers can be so difficult for me to translate to paper and to a text message. (I need a charting system)

Machine with MDI motion in X

halcmd setp hm2_5i25.0.stepgen.00.step.invert_output FALSE 0.0V
halcmd setp hm2_5i25.0.stepgen.01.step.invert_output FALSE =3.2V

halcmd setp hm2_5i25.0.stepgen.00.step.invert_output TRUE -0.4V
halcmd setp hm2_5i25.0.stepgen.01.step.invert_output TRUE -3.7V

Machine with NO Motion

halcmd setp hm2_5i25.0.stepgen.00.step.invert_output FALSE -0.2V
halcmd setp hm2_5i25.0.stepgen.01.step.invert_output FALSE 3.6V

halcmd setp hm2_5i25.0.stepgen.00.step.invert_output TRUE 0.2V
halcmd setp hm2_5i25.0.stepgen.01.step.invert_output TRUE -3.5V

I truly appreciate your assistance,

OK so if this is not a connector or wiring issue (screws not tightened, wire on wrong side of clamp, shorted wiring)
that looks like then step 0 output is bad