This keyboard had a lot of screws holding the top and bottom together so this little sound maker is built strong. The first issue even before the tear down was the batteries. They had badly leaked but at least the contacts were not too bad.
Once I took a brush to the contacts they cleaned up nicely.
Once fresh batteries were in place I turned it on and everything worked except for a single key.
Once I removed about a hundred screws, not really but it sure looked like it. I had my first look inside.
I next removed the two screws holding the switch contact strip in place and lifted up the strip.
The pads and switch contacts under them looked fine and then I looked closely at the circuit of the non working key and noticed this missing trace.
Added a small jumper wire to bridge the two copper pads and now all is better and this keyboard works like it came out of the box. This missing connection must have been a manufacturing defect yet the keyboard saw a lot of use or rough handling owing to all the scratches on the bottom plus lots of hair and dirt inside.
Like other thrift store finds, do not pass them up. You never know how easy a defective item might be to get back to working order :-D