Yamaha CVP-503 Key Cover hinge separated

(San Angelo, TX, USA)

My kids have used this piano for years now but when I looked at it this morning the hinge has coma apart on one end and the separation is spreading down the lid. I've tried finding a service manual for the piano because it doesn't look like it's difficult to repair but I can't find a manual. I'd rather have a few guide points before I just start taking things apart. The closest authorized repair center is 170 miles from me.