If you can hear the signal but it is super weak, first try to raise the output gain on your outboard or raise the input gain on the MD. There are some RAM sampling volume parameters that you can tweak for input gain and I believe the manual has a walkthrough.

Another possibility (I don’t know this for a fact) is that there is an input amp on the MD that has gone south. 99% of the time it is a setup/user issue as it all can be a bit fiddly, but maybe this is the 1%.