Cambridge Audio Tream Magic 6: Main Standby Swich does not turn off the device

[Golfino01]

I can not anymore turn off the Cambridge Stream Magic 6. Pushing the button on the front panel to change the unit to standby mode has no effect. The switch feel a little softer than usual, might be worn out mechanically. The unit does not react on any command by the remote control in any way. Could be problem of very old overstocked spare batteries, I have to try brand new ones. I see myself able to replace the main switch, where can this be bought? Any comments or ideas how to fix this one? Thx for any help,