MK118 FM radio only receives RTBF première

Still I would like to try other things if possible

Any means of detecting if PreFM circuit is OK anf FM demodulator is OK.

I have only a voltmeter to test things.

Do you have the adress of a supplier in Brusssel to replace TBA120U???
Thank you

There is not much you can do with a voltmeter, except checking if all parts receive the required power supply and you can check the tracks and connections for continuity.
Your Velleman distributor can supply spare parts