Volume synchronisation was introduced in April 2004. It only of use in non B&O set ups as the B&O ones control volume via Powerlink. If you have a non B&O set up and wish to use this facility, your Beolab 5s need S/W 2.5 or higher. This was introduced at S/N 17772145. The cable is a stereo mini jack cable and shouldn't be anything special. No doubt B&O will sell you one though! If your Beolab5s are older than this, they suggest setting the levels to maximum on each speaker and using the volume control from the non B&O system.

Thanks Peter!  Looks like my problem is the software version, the older one is just below the s/n you mention and has sw 1.5.  I connect them to non B&O equipment to an unamplified output, so I cannot adjust the volume from the non B&O system.  Do you know if the service providers can upgrade the software in the older speaker to sw 2.5?  Or is there a software available online that I can download to the speaker?

 Thanks again for your help.

they can program new software in to the lab5 through a notebook. latest software for your speakers is 1.62a

Just a quick note for those who have the same problem:  I got a technician to take a look and update both speakers to the latest software version, but it does not work.  The problem seems to be that the older one of the speakers is "Mac 1" and the other one is "Mac 2", two different generations and the Mac 1 cannot be upgraded to sv 2.5, just to 1.62.  Therefore it seems impossible to let them communicate via the sync port.

Thanks for your assistance!

sw 2.62 is exact the same as sw as 1.62a

sw 2.62 is for the models with pincode  sw 1.62a is without pincode

@Soundproof have you connected them to another brand (non B&O)