Yes, you can replace the AP35 cu with an ap20/21/22 and yes the R3000x
wil still work. You just need to check the software version in your
J-box.
You can see it at startup. I think that V1R6 will work just fine.
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Thanks, that's good information. Will Simrad upgrade the J-box
software at a reasonable price if needed? Getting the current version
number may be problematic since the display on my AP35 control head is
defective and getting difficult to read.