Switches
If any of the switches malfunction, and you can't find a replacement, it is possible to repair them with a little patience and skill. The most frequently faulty switch is the one on the left (ON/OFF).
From left to right: ON/OFF, Display, Sound.
If you have the right tools, it will not be difficult to desolder the switches.
A desoldering station is recommended, but at least a desoldering iron with a suction pump as shown in the picture.
With a small pliers they can be removed while straightening the pins.
This is the most frequently damaged switch, the ON/OFF one. One circuit is for 22V, the other for 7.5V. The electric arc causes the contacts to become damaged.
Copper contacts can be polished with very fine-grain sandpaper.
Restored contacts.
On the ON/OFF switch I use lubricating grease that prevents arcing. On the other switches, I use a "lightly lubricated" cleaning fluid, especially for switches. This extends their life.