There are a few possibilities.
1) SCR601 is turned on if there is a over current situation. It gets its gate drive from Tr03,04. need to check or remove SCR601 to see if it is that the cause. If so have to check scr or the ckt driving its gate.
2)Is Tr610 turned on? need to check if it is being driven. Normally, Tr610 is off and Tr611 is on depriving Tr610 of drive. Need to check out all the components in this circuit. Could remove Tr610 and verify that the relay engages. Do this with the speakers disconnected.
3) Is there +30V supply to the ckt? check junction of R620,R622,R623
4) C617 is the power on delay. It charges and always drive for relay drive Tr609
Good luck
Rick