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If all you want is to run a logsplitter, then you need the PowerBeyond kit for your tractor. It will cost about $250 from JD, and you could install it yourself in a couple hours.
I have installed the kit but it will not extend/retract the cylinder. I have pressure (loosened a fitting) but I assume not enough for any function. The splitter is ok as it operated fine when hooked to another machine. It must be an issue with the 790. Any ideas?