Marantz SR 685 Problems

[maynardb]

Hi,
i'm working on this Marantz for my son, and while I can fiddle my way around tube stuff, solid state is beyond me. The problem is when I power this up, if I keep the volume low, it works ok, but as I turn up the volume, it reaches a point where the power relays cut out and in. If I lower the volume back down, it will stay on, but will cut out again if I raise it up.
Any Clues?
Thanks,
Bruce