The Beomaster 6500 service manual you see for sale on eBay was 'taken' from here - I shall refrain from any other word. If you join as a silver member you will find that manual as well as all the user manuals for the 6500 system.
Whether this is sensible depends on how good you are at electronics and the equipment you have. The 6500 is a good amplifier so in my view well worth fixing. If there is no red light on the front, a component has failed - bit annoying as it was working initially.