The solenoid circuitry is disabled (not the power, the control circuitry) until the cpu boots so start with fixing your boot problem. Have a look at the following:

http://techniek.flipperwinkel.nl/ballyss/rep/index2.htm#flash

Check under playfield fuse and holder.

If the machine boots and coins up, you are getting the 7th flash on the MPU. The machine would not completely boot up without the 7th flash. If the flippers work and the knocker fires, then your problem is most likely the 1 amp slo-blow fuse under the playfield.

Problem is not with F4, at least not as far as your non-working solenoids goes. A couple of volts low won't prevent them from working. As others have said, start with the 1A slo blow fuse under the playfield. Test for voltage on both ends of the fuse. Even if the fuse is good, the holder could be bad.

Worst case is the fuse could be compromised or the fuse holder could be loose or there could be a poor connection in the wiring and you could still read voltage on both ends of the fuse and on the coils, but it couldn't carry the current required to fire solenoids.

Put a jumper wire across the fuse holder and see what happens. I have replaced the holder on most of my classic Bally machines. The factory used some pretty crappy ones. The clips break and still "look"ok........

That would indicate a poor connection at Pin13 and/or Pin25 on connector J3 of the Solenoid Driver board.

There's a little pot marked RT1 (upper left area of the solenoid driver board) to adjust the High Voltage for the displays. Slowly turn it to bring down TP2 to spec voltage.

In terms of flippers, go to the Solenoid Test mode (press the little red button inside the coin door 3 times). This will cycle through and activate a solenoid every second. The number on the display corresponds to specific solenoids being activated as per the list below.
When the display reaches 14, you should hear the Flipper Enable relay on the Solenoid Driver board click On then Off.
Report back if it's clicking or not.

6MDman-SDB-Test.jpg

You probably have a bad connector with loose terminals or cracked solder joints on the Solenoid Driver Board (SDB) or the Rectifier Board that needs to be repinned and/or resoldered.

Start a game:

• Press and hold a flipper button. Wiggle the J1 connector, J2 connector and Flipper enable relay on the SDB.
• Then wiggle the J2 connector on the Rectifier board - again while still pressing a flipper button.
• Do the same while holding the other flipper button.

If a flipper activates at any time you've found a connector with a bad connection you'll need to address.

If you want to drill further in and take measurements:
Since you're getting about 43VDC at the Flipper coils and the Flipper enable relay is switching on:

The Orange wire on both cabinet Flipper button switches connects to ground on the Rectifier board at pin 9 of J2. It's a single point of failure for both flippers so might be the culprit.

Both flipper coils have power on the outer terminal with the Brown wire. It should always be 43 volts.
The other outer flipper coil terminal: Orange on Right flipper coil, Green on left flipper coil gets switched to ground (0 volts) via the flipper buttons and flipper enable relay to put 43V across the flipper coil so it activates.

So: Right flipper coil Orange wire goes to pin 9 of J1 on the SDB.
The Left flipper coil Green wire goes to pin 8 of J1 on the SDB.
The flipper enable relay then routes these signals back out to the cabinet flipper button switches:
SDB Pin 1 on J2 (Red wire) goes to the Right flipper button switch.
SDB Pin 2 on J2 (Blue wire) goes to the Left flipper button switch.
These signals should measure about 43V when the flipper buttons are not pressed, and about 0V when the flipper buttons are pressed.
Happy hunting!

Cool.
Can you try something for me?

I found an undocumented DIP switch setting for Six Million Dollar Man that does some sort of display test. I'm not sure if it's known but someone may accidentally come across it if they've changed MPU boards or something and may think their machine is faulty.

If you put DSW 30 and DSW 31 "On" on the MPU board and then power the machine up, after the MPU test it should show "000000" in all displays and just sit there doing nothing else. Does this happen?

Great, thanks for confirming that

You need to resolder/reflow all those pins on the solenoid driver board. I suggest at the power supply board too. Cleaning is a band aid at this point.