Ok it seems it doesn't start up.This can be caused by a lot of things....
Thank you, I numbered your items for easier reference. I don't know with certainty how to check items 1 to 5, but I have answers for items 6 to 8, which I achieved with the unit powered on, and the MIDI board cable connected (the attached photo of what I think is C131 has the MIDI board cable removed for clarity). Maybe these answers will help to narrow the possibilities.
1) Could be the diodes D38,D39
2) No clock signal (bad crystal,bad C143,149,bad U41)
3) Bad reset circuit
4) Voltage too low
5) No interupt pulses at pin 16 of U29
6) Check pin26 of U29,should be 5V.If it's low it will keep the Z80 cpu in reset mode.
ANSWER=5.07V
7) Also try to start it up without the tubes and see what happends.
ANSWER= All of the LEDs to the right of the display cycled once extremely quickly and then went out, nothing more.
ANSWER= I'm noticing now this is randomly happening on several power cycles whether the tubes are in or out.
8) Measure the voltage over C131 (3300µF/16V)
ANSWER= 11.87V (with Tubes)
ANSWER= 13.50V (without Tubes)