YES! I HATE Sony!
They REFUSE to fix my BROKEN/NON-WORKING
MDS-JA3ES Minidisc recorder!
They INVENTED this format!
They should fix my unit!
It WON'T TURN ON!
I have 2 of these SAME exact units and they BOTH have the
SAME PROBLEM!
They WON'T turn ON!!!!!
First of all those units are 14 years old, and Sony are under no obligation to fix a units that old. They may not have parts. If there is a chip that causes this malfunction it will almost certainly be NLA by now. In general only one chip run is ever done and when they are gone they are gone.
If you want to run vintage equipment you will have to take a course or do intensive study in electronics repair and make a highly significant investment in test equipment.
Your other option is to buy a different recorder on eBay. The next option is to find a service person probably on the NET that will repair vintage gear. If they are good they usually charge a high premium for their services.
I have located a service manual for your unit, but have not downloaded it as it will cost me money.
Sometimes with older units if a part id NLA there is a work around, but more often than not there is not. The fact that you have two of these units with the same problem suggests some sort of design problem in the turn on circuit or power supply. I have found out they have an unusual power transformer. Unusual often means trouble. If that is the problem the units would likely not be fixable or need extensive redesign and work around.
Minidisc is an obsolete medium and a lossy recording system at that, so those units would not be something that I would think would be worth extraordinary effort.
I love vintage electronics and service it, see my signature. But I'm highly selective about what units to put real effort and time into.