Yes, this is a common problem, and yes, it can be fixed.

Just replace the shiny, black bowl with a new one - they are still available from Beo.

You`ll need a screw driver.

Stefan

Thanks, I'll try that!

So you mean that the problem is that the bowl is scratched or something?

The core principles of the LC2 dome sensor are based on one of Faraday's laws related to capacitance which is measured in Farads after Michael Faraday and capacitance is normally quoted in MicroFarads (10 to the minus 6) or PicoFarads (10 to the minus 12)

In the case of the LC2 we are talking about capacitances of between 25 and 75 Pico Farads and the dome whilst made of plastic is part of the dielectric of the capacitor. Below the plastic dome is what looks like normal rubber, but is in fact conducting rubber like material which joins the dome and the IR PCB. To stop stray interference/capacitance the IR board are as near as possible to the plastic dome and if not fitted correctly will stop the "touch" from working.

Below is the circuit which the Dome (Capacitor) is connected too.

The ST6220 microprocessor produces a strobe signal and when you touch the dome a capacitance is produced which switches the transistor TR3 and provides a pulse stream back to the microprocessor. Depending of how long you touch the dome defines how many strobe pulses goes back to the microprocessor. The processor counts the pulses to determine if you are switching the light off/on or dimming etc.

As stated the plastic dome is often the cause of the problem..

Hello Keith,

it is an old story, but can you still help me on the schematic diagram of the B&O LC2 type3120 Light Dimmer? I hate to see old stuff go to the trash..

TY Brasto