I am by no stretch of the imagination an expert on Sys 80b games .... ..... but I'll throw in my thoughts ...

I recently had a Night Moves issue , the 5v was super low and so it wasn't booting. After some head scratching and metering I found that the ground connection from the 12v bridge was bad. Remade the connection and all good again.

I wonder if during your ground modding a connection has been missed, needs redoing ? It's straightforward enough to check continuity from bridge to the ground connection.

One lug of the bridge has a single ground wire attached. Check continuity between the it and the grounding point. You can do this with power off.

Yes. Isochronic_Frost As wayout440 suggested above ...check at the power board first to see if you have 12v supply there.

This below taken from http://pinwiki.com/wiki/index.php?title=Gottlieb_System_80#Recommended_Repairs_for_the_System_80B_Power_Supply_Board

*Note* the part about 5v readings being below 1v. It suggests grounding issues. That was the problem on mine when I had about 0.75v instead of 5v. The power board was perfectly fine.

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5.5.4 Recommended Repairs for the System 80B Power Supply Board

System 80B +5 VDC Power Supply. The adjustment POT is at the top of the PCB.

Step one to improving power supply reliability is to replace the original 500 ohm 1 watt adjustment pot. This procedure can be done easily without removing the large heat sink. A replacement sealed pot is recommended, but not completely necessary.

Next, remove all the old solder from the all of the .156" header pins, and reflow new solder onto the joints. The top header pins (J2) supply +5VDC to the majority of the associated circuit boards in the back box. Provided that the power supply is delivering acceptable voltages in the +5VDC range, these two relatively simple repairs are the only things needed for this board.

However, if you've adjusted the pot as much as possible in the appropriate direction, and the power supply is still delivering voltages higher or lower than around +5VDC, it's probably time to look at replacing the LM338K voltage regulator. While not a frequent occurrence, the voltage regulator will sometimes fail.

If the voltages measured are less than 1VDC, the grounds for the power supply (located at the transformer panel) will more than likely need attention. Once the grounds at the transformer panel are better secured, recheck the voltage at the power supply.

Note: When measuring the +5VDC provided by the power supply, first disconnect J2 on the power supply. Measure power at the J2 male headers first. Once within an acceptable range, turn power off and reconnect J2. Measure power across C1, the 100uf/10V capacitor that is next to J1 (power connector) on the MPU. The MPU may drag the +5VDC supply down a bit. If you find this to be the case, adjust the trim pot on the power supply until a steady +5VDC is seen at the MPU. Poor connections between the +5VDC power supply and the MPU board may also reduce the voltage measured at the MPU.

So you *definitely* have 12v going onto the power board ? - you measured this at connector J1 as described a few posts above ?

With J2 disconnected - what reading do you get at the J2 pins ? If you adjust the pot does the reading change at all ?

We've all done it. Glad its sorted.

A good reminder though that you can't check a fuse just by looking at it