As the previous poster suggested,you should be able to hear some noises when touching the phono socket connectors on the Beomaster.

There is indeed(or should be!) an RIAA preamplifier built into the BM5500,but it may be faulty.It has a dedicated internal supply.

Also it's common for the connections of the phono socket to become dry jointed with age and movement.

The sub board that carries the sockets connects to the main board via an edge connector.This too can be become broken.

It seems as though the Beogram is sending audio,as you can hear it faintly via the higher level input.

I think you will need to investigate inside the Beomaster.

Nick

UPDATE: 

I conneccted the Beogram 5500 to a Beocenter 9500 now it works sound is coming out!!

This means both the Beomaster 5500's I tried it on did not have RIAA pre amps?!!

The problem now is it only plays for 30 seconds tonearm lifts up and it then switches off...

Also the stylus is producing very distorted sound.

How do I fix the distorted stylus? And the stopping after 30 seconds?