Tandem Y Axis not working on 7i76E

Please delete

Are you using jog?

As tandem axis has to be homed first before you can jog

TEST files attached as requested.

@ Clive S  not using jog period. I'm simply loading up and mashing "HOME ALL".......
 

I only see three joints in your ini file.

Joints = 3

Should there  be 4

That was a different set of files @Clive.   There was only to be X, Y and Z running naked......

Yes. But you stil have 4 joints x-y1-y2-z that is 3 axis 
I am confused now
I have just looked through your files and it seems you have only a Y1 

With a tandem axis you need Y1 and Y2 in both HAL and INI file

Yeah, there are just 3 stepgens in use there, should be 4.
Question, when using this test config and changing from one to the other Y joints, do they both move in the same direction when jogging?
One more thing, no homing with the test setup. Just jogging.

Possible PNCCONF issue?

Yes, PncConf issue, it does not create 2 joints for the same axis, just one.
Does not matter as there is no need for it, except for some initial tests to make sure both tandem drives/motors are spinning the same direction.
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I think it's time to make a new config, tandem one with everything set up, but first do
sudo apt update
sudo apt upgrade
maybe there was something iffy in your build.