I`m not familiar with the FT40 amps, but hopefully there are marked what is +volt and - volt and ground. On the PT showcards i seen to recall that Ground is common for both X and Y. You can look on the backside of the card to see if ground is common. (In the same "path of metal"). If so, you`ll sort it out.
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More projects than time available.
More projects started than finished.
More money spent than earned.
More failure than success.
Just got to love lasers!