Quoted from Billc479:

Back to basics - check your supply voltages from the rectifier and solenoid boards. Pinwiki has a good guide for these Bally machines.
A few pics of the rectifier board and MPU will also help us in troubleshooting.
Is there a pattern to the rests? For example, only when hitting “X” target, only when using left flipper, etc.?

Quoted from Billc479:

Boards look good - new, and nothing jumps out at me on the boards.
On the rectifier board, why is J2-10 taped? That is the power ground for lots of stuff. I am guessing it is a splice. Verify its good. Also, while there, give a slight tug on J2-9 & 10. I want to make sure those crimps are solid and they are locked into the connector.
Speaking of connectors, look at the MPU, J4 connector and see if you can tell whether it has been repinned. You will have to unplug it to look. While its off, look at J4 on the board and see if you any green "watery" looking stuff - that would indicate it was mated with corroded pins, which means J4 had not been repinned when the board was replaced.
The intermittent nature, along with new boards, makes me lean toward a connector issue. (Is the ground braid in the bottom of the head secure? There should be a screw or something holding the ground braid to braid from the belly of the machine.)

Quoted from Billc479:

Rectifier J2-9 is return for the flipper switches, so I doubt that was the issue. If the pin stayed in the connector, then it should be fine.
Do you have a spare MPU so that it can be ruled out?
What is making this difficult to find is the intermittent nature of the problem. My intermittent problems usually pop up on my machines when I’m having one of the best games I’ve had on it for quite awhile, and then, clunk.
Hopefully, others will chime in with ideas.

Quoted from Knxwledge:

Is your solenoid driver board new too? Maybe could be an issue with the 5v regulator on it if it's an original board

Quoted from MrBally:

Agreed, Sea_Wolf, post a pic of the Solenoid Driver/Voltage Regulator board.
Also, have you repeated the socketed IC's on the MPU board? Support the board if pressing on the IC's in an installed board.

Quoted from mrm_4:

I started having the exact same problem on my Mata Hari. I figured it was because I need to repin connectors. I checked the voltages on my SDB and all the test points were dead on 5v or 12.5v which is why I’ve been thinking connectors.
I have crimpers but man I hate recrimping no matter what I do it looks terrible and I feel like the originals were better off when I’m done haha

Quoted from Knxwledge:

He means to reseat the ICs by taking them out with an extractor and putting them back in the socket. When you push down on them, put some support behind the board so it doesnt flex.
But new solenoid driver board... Im fresh out of ideas. Seems like it has to be a wiring problem somewhere. Maybe check the main AC cabinet wiring and see if anything jumps out at you, then I would start repinning all the connectors that haven't been repinned yet that deal with the 5v supply
Maybe contact barakandl and see if you can send the MPU to him for bench testing

Quoted from Billc479:

Sea Wolf -
On the MPU board are several ICs (chips) that are in a socket. In other words, they can be removed from the board without desoldering. What MR Bally is saying is to pull up on them just a little bit, and then push them back down into the socket. Sometimes a chip will get loose, and reseating (He had a typo, which may have caused the confusion) the chip clears the problem.
If you go this route, you should take out the board to do it. You don't want to flex the board - flexing may cause cracks in the runs and lead to other problems. Before doing this, I would remove and reseat every connector to the MPU and see if that clears the problem. If you remove the board to reseat the ICs, you won't know if reseating the connectors or reseating the ICs was the cure.
I'm not sure what to think about the 20 minute wait for it boot. It could be a bad capacitor on a power supply. The next time this happens, take voltage readings on the rectifier board, SDB, and MPU. The boards should have test points to get these measurements.

Quoted from Knxwledge:

In your collection it says you have an Eight Ball. Could try taking the MPU in the Mata Hari and testing it in there. Don't forget to change the dip switches on the MPU when swapping games

Quoted from Billc479:

Did you get any voltage readings when she stopped working?