It's not mad scientist territory
I replaced my power transistors to still have no output and 6 volts where there should be 42 volts.
I've got 42 volts at a voltage regulator and this was dropping to 6 volts at fuse 4 (another blown power transistor with another component causing this - parts on the way).
Fuse 4, a PTC self resetting fuse, was where the voltage was dropping down to 6.
Actually theres quite a few on the board, they look like yellow lollypops.
These fuses guard against over-current situations. Then once the issue is fixed/resolved they reset.
So on your main board, when it's printing correctly, you should have 42 volts at both legs of fuse 4.
Now my theory is something amongst the power transistors is faulting out, likely due to temperature, thus overloading fuse 4, which radically increases it's resistance, dropping the voltage.
Once that happens, ink output stops.
So to test this, set it printing, check voltage at fuse 4, should be 42 volts on both legs.
Once it stops outputting ink, leave it printing and check the voltage at fuse 4 again, the upper leg will have 42 volts, the lower leg will have much less if any voltage.
You only need a cheap multi-meter for this and use any of the TP (touch points to ground) for the common/ground lead, I just pop my lead into the loop and let it hang, that way you only have to concentrate on one lead.
Check the lower leg of fuse 4 for voltage, less than 42, the issue is amongst the power transistors.
If the upper leg has less than 42 volts, the failing component is back towards the upper left corner and possibly the voltage regulator attached to the heatsink.
How long before it starts printing correctly again for you?
peace out