Does it work if you disconnect the two BL4000s?

Had not thought of that. Unfortunately same result.

Load button for CD works.

It does confirm option setting indicating that infrared works. But pressing CD, RADIO or A.AUX does not turn it on via remote or physical buttons.

Will try another power off cycle. Wait 45 min and check if it asks for PIN.

I was just about to ask if it could be a PIN code problem.  Do you have the PIN?

If you have the service manual there are all sorts of test modes that you can run to check (eg) the keyboard.

The keyboards of these systems (and 2300, Ouverture) have been know to malfunction because the foil breaks - however it is unlikely that this would stop IR control, unless the failure is an 'always on' condition. 

Yes, we got the PIN. So will try again in approx. 30 min.

If this will work we will disable the PIN funktion.

Except for the LOAD button the system is always controlled via IR.

You are right

It is the PIN code system which is screwed. It does not prompt for PIN as it usually does. Will have to study the service manual.

Had no luck bringing Beosound 3000 back to life. Based on some more googling it seems like the EEPROM is dead.

Took it out of the equation.

The BL4000 are now connected directly to the ChromeCast audio which used to be connected to the Beosound 3000.

And the BL3500 MK1 got its own ChromeCast audio via the MCL socket.

Multiroom the Google way....