How can I fix my Technics SU-X520D?

Hi, I have had this Technics SU-X520D for about 15 years and I'm very keen to mend it if I can. For the last few years, the amplifier sounds like it has power but the lights don't come on. By thumping it on the side, it lit up and worked fine - this worked every time. Now, it has given up all together. However the power is clearly still there because it warms up as usual. There must be one loose connection or a part must need replacing but I can't see which this would be. If any one can help I would be grateful!