Retrofitting a 1986 Maho MH400E

Thanks, I wired TB1-3 to the same 24V power supply so it should have the power now (ground is common so I needed just the power, right?). But it doesn't solve the problem, when I connect the wire to TB2-17, which is output 8 and have hal do the following:

net machine-is-on hm2_5i25.0.7i84.0.2.output-08

The drives don't stay powered after I release the button. Whereas when the same wire was connected to an output on the 7i77, everything worked fine. In fact, as I said before, both yesterday and today morning it worked with the 7i84.

EDIT: it's acutally 7i84.1.5.output-08, since it goes through the 7i74.

I checked it with a meter and it shows 24V on both TB1-1 and TB1-3.

What output is the 7I84 (now 7I77) driving and does it have a flyback diode?

I'm concerned that if a 7I84 output is damaged you may also damage the 7I77

Also make sure that no field power to 7I77s or 7I84s is switched by a relay or mechanical switch. This can damage the output drivers (the field power should be wired directly to the field power supply or via a fuse, never a relay or switch)

Intead of choping the ribon cable ,you can use something like this.

All the power to the cards is from Meanwell 24V and 5V PSUs. I did "daisy chain" some power connections from one card to the other.

The 7i84 output signal is in the attached schematic - it's the signal 28X1-2, from TB2-17, on the left. I suck at electronics so I thought it'd be better to attach the file rather than try to explain what it shows.

EDIT: BTW, this is Mark's diagram, so it's the setup he uses with success. Could I have damaged the output by using it without having power connected to both VFIELD A and B?

19k1 relay should energize as soon you give power with the Q1 switch (big red in the back of the cabinet). If it is not than probably tb2-17 from mesa 7i84 is not output 24 volt for some reason.
John