There is not much information out there about your model keyboard but I managed to find the [http://www.vintagemanuals.com/manual/Radio+Shack/42-4022%2C+Concertmate+680|service manual] online, (if you wish to purchase it), which should be of some help as usually most service manuals have dis-assembly instructions and schematic diagrams
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If there is no indication of power when the power is switched to On then you will have to open the keyboard and check the circuit from the power supply input to the switch and then through the switch and further into the circuit.
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If there is no indication of power when the power is switched to On then you will have to open the keyboard and check the circuit from the power supply inputs, both battery and adapter (although they should common up somewhere near the power switch) to the power switch and then through the switch and further into the circuit.
Hi,
There is not much information out there about your model keyboard but I managed to find the [http://www.vintagemanuals.com/manual/Radio+Shack/42-4022%2C+Concertmate+680|service manual] online, (if you wish to purchase it), which should be of some help as usually most service manuals have dis-assembly instructions and schematic diagrams
If there is no indication of power when the power is switched to On then you will have to open the keyboard and check the circuit from the power supply input to the switch and then through the switch and further into the circuit.