M44 in protection mode

[PGjunkie]

My M44 will goes to protection mode (orange light on) after about 1 hour of play or ideal. It will need about 2 hour to rest until I can turn on again. I touch the heatsink, it is not hot at all just slight warm.
Can anyone tell what should I look for or change?
Recently I change all the capacitors on it to new one, except the big blue rail cap as Farnell doesn't has stoke.