Technics amp playing up?

I found a great technics stack system at a car boot sale yesterday but cant get it to work. I have just attached the cd player to the amp and then the speakers. I can just about hear the music very softly if I turn up the volume all the way. The same with headphones plugged in. I can only hear very faint music. The amp is a SU-X990D. CD player is SL-PJ25. Any help would be much appreciated