I will answer your next question before you ask it..
QUESTION -- How do I switch a Beolab 3500 from Masterlink to MCL (Master Control Link) and back again ?
ANSWER -- To use the MCL if the unit is currently set to Masterlink you need to enable it via a service menu command. To get into the service menu to switch between ML & MCL press MENU then MENU then 0 then 2 then PLAY, then use the up arrow to switch, then STORE.