Yamaha Electric Piano power stuck on – LED won’t turn off
As a Yamaha warranty and service center we have a reasonable number of enquiries for the P series pianos, they are popular and available at good prices second hand. With a weighted keybed from the P90 series up they offer a great experience. The only thing against them is that they are getting older, Yamaha still have good support for parts though so fear not.
What causes the piano power LED to be stuck on?
The P series has what is known as a soft on / off power function. When the piano is off by appearance there is still a small amount of power running inside to enable the piano to turn itself on if required by the touch of a non latching power button. Once turned on the keyboard electronics tells the power circuit to stay on until the power button is pressed again.
You may notice that when you have a stuck on function, the piano boots up the moment the mains adapter is plugged in, if you hold the power button the piano will appear to switch off but the power light remains on. No other features work, nor sound and the piano cannot be turned back on with the button press. You physically have to remove the power and reapply.
The reasons for this are as follows:
On startup the piano waits for the power button to be pressed, when pressed the full power runs to the CPU which then triggers a reset pulse to start up the processor properly, this then holds in the power supply to keep it running. On pressing the power button to turn off, this signals the power system to shut down, a shutdown occurs with some simple logic derived from the power supply knowing if the piano is on or off already and then shuts down. In a powered off state all power is removed from the CPU and it can be in a ready state to reboot when power next applied. If however you have the issue of power being stuck on, the CPU first resets on main power being applied, but even though pressing the button signals the CPU to shut down and issue the correct shutdown commands, the power section fails to turn off, as such the CPU is shut down, but still has power on it. Without a power cycle it is unable to reset, as such will just sit there.
Fortunately this is something we’ve fixed many times on the P90, 125, 145, 225, 525. Get in touch to discuss repair of your piano!