Retrofitting a 1986 Maho 400E

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

No I am wrong. The 19k1 should energize as soon you press power bouton in gmoccapy.
John

Yes, that's the problem. I can solve it by moving the wire to the 7i77 but now after what PCW said I'm afraid not to damage that board. I would very much like to know what happened before I move forward, and yet I don't really have any time to do so. This machine must be up and running ASAP or my little operation is going to be in serious trouble.

By the way, don't these 7i84 have overvoltage protection and whatnot? Would one really get damaged from outputting 24V with only one bank of field power connected? Should I order a new board while EU surplus has them in stock?

It says in the manual that if only one power source is present, the card shouldn't work. But mine did. Also, CR7 is green in LCNC and CR6 is off, I don't know if there's any other indication of field IO faults. HAL shows pins. It looks like the board is okay, so why doesn't it work?

I don’t think you have damaged the board, chances is that you have make a mistake in hal syntax and the output is not energized. Try to energize a not connected output of the board and use a multimeter and see if there is 24 volt out.

I dont think a unconnected field power would cause damage but its not an expected mode of operation.

The 7I84s output drivers have short circuit protection and inductive flyback
protection but there are things that can damage the outputs:

1. Driving inductive loads larger than about 60 mA that have no flyback diode.
2. Switching the field power power with a switch or relay (this can cause
a voltage surge that exceeds the voltage rating of the output chips)

How can I drive an individual physical output pin from hal to check the voltage?

Easiest way is open a terminal and use halcmd:

halcmd setp big.long.pin_name true
halcmd setp big.long.pin_name false

you can get a list of the pin names with:

halcmd show pin *7i84*