trapezium

Hello- First I am somewhat new to the mini-disc world. I have become the archivist for a band. They record many of their shows using a MD player (Sony MZ-R909). I purchased a mini-disc player/recorder mainly to play the MDs from the band to get them into my computer. I also wanted to be able to record shows for myself. I picked up a used Sony MZ-R50. I tried playing the show discs and they would play, all tracks showed up, but there would be no playback level on the level meter in the display, nor is there any sound coming out of the headphones (or line out). I tried three discs given to me by the band. No sound. Tried different headphones, could hear the audible beep when "play" or "stop" was pushed, but nothing else. Did check the volume. Checked all the different buttons on the unit, nothing set incorrectly as I could see. Bought blank MDs and tried a basic recording on the unit. Played back recording and it worked fine. So I cannot complain to the seller, as the unit does record and play. It just does not play the MDs I got from the band. Went to a friend that has an older Sony MD, tried the MDs the band supplied and they worked fine. Put one of her recordings in my R50, and the same problem. Disc plays, but no level or music. OK- Question, is there a compatibility issue I do not know about? Or do you all think the unit just has a problem? Unless there is something I am missing, I plan to sell the unit and buy another. 2nd question- can you recommend a unit that is compatible with discs recorded on the R909, and also allows me to change levels on the L & R separate while recoding a live show. Thanks Much!