Piano repair action:
2 keys did not work on the Roland HP136 digital piano.
1 black key was repaired by pushing back a metal part underneath the key.
The other key needed a rubber contact replacement.
Page www.bustedgear.com contains information which rubber piece to order.
It is a long rubber piece containing 12 contacts to connect 12 keys, with each 2 carbon electrically conducting parts.
The picture below shows the opened top view of the electrical piano with 5 red (screws) and 5 blue circles (position of screws). These 5 crews should be unscrewed in order to be able to open the cabinet of the electrical piano.
Manual of the Roland HP-136 Digital Piano
Electronic piano is repaired by cleaning the PCB with benzene and replacing the rubber part containing the electrically conducting dots, probably made of a substance with graphite. What we saw right after opening the electrical piano is depicted on the right (before cleaning with benzene).
The damage seems to be created by having a current flowing for a long time with the key down. Probably the electrical piano was switched on for a long period of time with an object pressing the key down.
A design improvement for the piano would be to decrease the current flowing trough the graphite containing material and/or a optical indicator showing a key is pressed for a long time, especially when the audio volume is turned down.
