I bought an MZ-N707 off ebay a while back, it worked for a while but then one day didn't work. I was looking at the battery terminals and they looked a bit green - so I took the casing off, and sure enough the positive terminal on the battery compartment is corroded, along with some brown marks on the PCB around the side of that. One other thing is that it already had the MZ-N909 'hack' on.
When I put in a battery or put in a disc, the display does go a bit dark, but nothing else happens - and then it powers down, just like if you didn't put in a disc into the player but pressed a button. There's no motor noise - just the display going a bit darker.
I have cleaned the contacts on the battery terminal but beyond that haven't done anything.. Is it rescuable?