I have found that the female connector that received the data cable wears out on the mx-850. The male plug that is used on the 850 data cable is a common mini stereo type plug but it is available in both 3mm diameter and 1/8" diameter with 1/8" being slightly larger than 3mm. If you can find a cable with a 1/8" plug it may work in a worn remote where a 3mm plug has failed. A little electronic parts cleaner could also help.

Mike.