It's 20+ years since I worked on one of these, but I recall problems with the solderring of the power regulators causing your symptoms.
If the +5v supply is missing, the whole circuit will shut down.
Sadly, all the manuals I had for Technics products were disposed of (in the skip!) before I could get hold of them when the firm closed its service department.
(I was hospitalised at the time.)
Tony
I suggest that you check especially the accuracy and purity regarding noise and ripple, of the +5v, as this is fairly critical to the correct operation of the circuit. Tony.