That command : load 4 2 12 is a command used in the SX-2000, not the SX-200. Actually, I just used the command today. Yes, after the command wait a minute or two for the card to load.
You can also issue the command: STat 4 2 12 and you will get a display of all the circuits on that card slot and their status. If you issue that command too soon after the load command, you will see a message that reads something like there is no card in that card slot. Don't worry, wait a minute and try the STat command again.
Good Luck!
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My Biggest problem is that I almost always believe what I tell myself.