if d4 on my schematic is not lit, then q1,q9,q10 are a problem. 2sa1413 are easy to get (to252 version required)
OR... input fet is toast.
I have change now to new parts the fet q1a/b 2sj74 and q1, q9, q10, d4 (your diagram)
But d4 still not light, and on output +280v to ground.
After remove fet q1a/b, i also solder out line input to R2, in this case one side of R2 is not connected more to any part.
I still meassure 3,00k instead of 1,00k at right channel.
it looks for me, stax factory put 3k on left channel...
additional i have meassure on all resistors the voltage drop at left and right channel.
I list here only the resistors i found with different values between left and right channel. (Your shematic) (power capacitators running on 280V+280V=560V )
R5 L=4mV R=77mV
R6 L=8mV R=69mV
R11 L=+280V R=-140-240V (only on right channel D2+D3 Brightness go up, and stay with higher brighntess, to the point if switch power off)
R12 L=+280V R=-240V
R15 L=301mV R=813mV
R17 L=0,36V R=1,07V
R18 L=0,36V R=1,08V
R21 L=280V R=269V
R22 L=33mV R=12,46V
R26 L=19,9V R=54,0V
R27 L=9,8mV R=6,1mV (Additional part on my board, i painted in your shematic)
R28 L=9,7mV R4=5,8mV (Additional part on my board, i painted in your shematic)
TVR1 L=57mv R=201mV (Additional part on my board, i painted in your shematic)