Sounds like the latching mechanism for those switches is gummed up,, probably the old lubricant has gone hard with age.

 I'd expect that a clean out with switch cleaner, not in the switches themselves but on the moving parts will sort this out.

   Had the same problem with my a Beocenter 4600 I used to have. As casdave has said, the old grease goes hard and makes a wonderful glue. Never got round to fixing it though. even though it was in daily use for about 2 Years. What I was told to do, was to gently pull the front of each switch. Clean out the old grease and this should solve you problem.

Craig🙂

Wonderful machines but a bit ackward to service the front panel. 

Stuck pushbuttons is a common problem.
Like Craig suggests, note the positions and pull off all the push-buttons.
Carefully and patient levering off using a wide flatbladed screwdriver set in from below may be the only way. Put something between to avoid scratches.
Clean the metal bracket that each button slides on.
Also clean the square channel in the buttons plastic backings.
Pipecleaners soaked with isopropanol are great for this.
Add a little amount of fresh silicone grease to each channel and
mount again.

The above applies to
Beomaster 1400 (80's)
Beomaster 1500
Beocenter 2600
Beocenter 2800
Beocenter 4600

Martin

Thanks! Martin, I was just trying to put the put the pictures on the site, when I read your post. This is exactly what I have done, even including the silicon grease. They go like new now.

And here is a picture of the "pipe cleaner". These are actually ment to brush teeth 🙂

 On the right is one of the fronts.
 

Nice work !

🤒

Martin