Thanks again Guy,
My further investigations: as I have a Beocenter 7700 I tried to use the MCL2A as it was intended. Beocenter has no speakers at all. Speaker ribbon from speaker 1 or 2 (didnt change anything) to the white box and there, IR eye hard wired and beovox connected.
On the eye. The red light glows when receiving IR and according with the press of the key.
The Mute key do bring music on ad off on the speakers.
A long press doesn’t put the Beocenter on standby or a simple one doesn’t bring it to life.
Volume commands through IR are received (led blinks) but no effect whatsoever.
The faulty IR board do light up the mute led but doesn’t react to IR (capacitor ?). When you touch the little pins that must be the socket for the keyboard I guess, the relay does click in and out and de mute led light accordingly…