Yamaha CP70B repair
Fix the Yamaha CP70B electronics by eliminating them altogether and
make the CP70B sound better!!!
Bypassing that old 1980’s circuitry is simple and makes the Yamaha Electric Grand more reliable.
My Yamaha CP70b Electric Grand Piano has been very reliable and it stays in tune for ages. 3 years ago the electronic part of it stopped working. I found the schematics for it at http://www.synthfool.com/docs/Yamaha/Yamaha%20CP-70B%20Operating%20Manual.pdf , and a forum for it at http://www.pianochopshop.com/forum.html and I finally diagnosed the problem to a poor connection on one of the pins.
While searching the net for answers I discovered that the Yamaha can be connected to an amp, UNPOWERED, just like a guitar. This bypasses ALL of the circuitry, which is one less thing that can go wrong, but more importantly,
IT SOUNDS A LOT BETTER!!!
The bypass is so simple it can be done by twisting wires around 3 connectors, no soldering or electrical knowledge necessary. I tested the piano by playing for 10 minutes or so using the onboard pre amp that I had fixed and then using this bypass method. The difference was quite audible, less bass boom being most noticable. The stereo tremelo effect is lost but that is a small price to pay.
I preferred the bypass sound so I decided to make it permanent. I didn’t cut any wires and the process is completely reversible.
Simply connect the WHITE wire from the piezo’s that goes IN to the board, with the RED and WHITE wires that come OUT of the board. Obviously these wires must be disconnected first from the board. Leave the EARTH wires connected.
At the left end of the circuit board behind the Volume control, these RED and WHITE wires are pushed onto pins in the board. They go directly to the OUTPUT – XLR and Jack sockets.
At the right end of the board the positive WHITE wire and it’s Earth come from the Piezo pickups and go into the board. You can see the pin and the wire connector I have pulled off it.
Disconnect the RED & WHITE Output wires. These are the LEFT & RIGHT output wires and need to be connected together. Solder or wrap them together and join them to a length of insulated wire.
Solder or wrap the other end of the new piece of wire around the connector on the WHITE input end and then tape it up.
The circuit is now bypassed. I take the output from the mono jack sockets to the CD input on a Yamaha home stereo amp and I have about the same volume as a standard piano. I am enjoying the new sound, it hasn’t lost that signature CP70B timbre, but the bass is much clearer and more natural.
Here’s an overview showing the grey wire I used to bypass the old preamp. The Yamaha doesn’t need any power now and I can undo this bypass simply by unsoldering the wires and poushing them back onto their connector pins.
Kudos to whoever invented this simple fix for old electronics. I got my info from John Smithson at the Yamaha CP70B forum. Thanks John!