I traced out the local circuit for the first two pass transistors, and it looks like two instances of a pretty standard op-amp voltage regulator. Working that, I found the problem, a corroded trace junction at a via where the reference and cathode pins of the U155 (LM431 zener shunt regulator) that provides reference voltage for the op amp regulator are joined. The trace to the reference pin was open, causing the output to float high. You can see them beautifully pristine in your photo coming from U155. Mine were not so shiny, but I really couldn't see any trace disruption or very much corrosion at the via, but it certainly failed!
When I patched that, the reference voltage fell to 2.5v, and the two rails linked to it dropped to 3.27 and 2.80 volts. So that's good. The output from the third regulator (should be -2.6v) is still wrong, so I'll look into that next.
So unfortunately, then there's been overvoltages on most/all rails (4.2v instead of 3.3 or 2.8 ). I wonder if that was enough to kill the ASICs, CPU, or other special chips?
There are two ASICs. One for acquisition and another for the display. I believe the display sends clock to the CPU.
The display ASIC and the memory gets 5V from the power supply board directly. And I believe all the other ICs are the same including processor. As you are getting clock out of the oscillator means you are getting the right power on that side of the board.
The acquisition ASIC is the only that gets around 2.8v from these regulators and transistors from all I could find.
If they killed anything most likely just killed the acquisition.
The system will work without the acquisition, it will just fail self test and wont get any signal. But all the other things should work, like display, menus, calibration, etc...
My piece of advise would be to:
First - Fix any damaged trace. With broken traces you cannot test anything.
Second - Check if you are getting 5v on any trace on display ASIC and its memory, processor and all it's surrounding ICs.
Third - If the ASIC gets power but do not pulse any data or clock to the display connector your ASIC is likely bad.
Fourth - If the processor gets power but do not pulse any data from any connector then the processor is likely bad.
Leave these transistors and acquisition ASIC as the last thing to fix.