Since it's with both MPU's and all displays, I'd agree. However, the credit display uses different voltages than the score displays. Therefore, check the ground. It's daisy-chained from one connector to the next so your issue is somewhere before the first display connection.

How did it go? Any update?

I'm assuming you attempted to measure these voltages at the display connectors? Remember to set meter to read AC.

It comes straight from one of the main transformers in the bottom cabinet. Since you have ground and there are two different voltages missing, the only way you'd have no 5 VAC (or 6 VAC?) and 3 VAC voltages at the displays, is if something wrong at this transformer.

What about the 60 VDC and 42 VDC that drive the displays? These both come from the A2 power supply. Since the 42 VDC is derived from the 60 VDC, maybe you are simply missing the 60 VDC? Something wrong with A2 power supply seems more likely than something wrong at the transformer.

Verify 60 VAC coming into A2 power supply at J1 across pins 7 & 8.
Verify 60 VDC at test point 1 on the power supply.

Pin numbering matches up, so yes, it seems so.

FWIW, in the Caveman (80A) manual, it's showing 5 VAC all the way through...

Screen Shot 2022-09-03 at 12.22.56 PM (resized).png

So if the transformer is working (5 or 6 VAC, and 3 VAC) but displays are not, then all that's left is the wiring in between. Simultaneous bad wiring for two different voltage circuits? This seems highly unlikely unless you've accidentally cut through a bundle.

Forget the wiring harness for now. You're looking for something common to two different voltages on all displays. I'm going to bet you don't have 60 VDC coming out of the power supply. Without the 60 VDC, you can't have 42 VDC, and none of the displays will light.

Take a quick peek at Test Point 1 on A2 looking for 60 volts DC.

I’m reading 19 VDC on my brightest score display grid and something between 24 and 28 VDC on the others.

On the A2 power supply, look at connector J1. Pin 6 (5 VDC) and pin 9 (8 VDC) are the DC offset voltages that are coming from A2 and being sent to the transformer to offset the AC voltages.

The AC voltages at the display boards have already been offset at the transformer...

Screen Shot 2022-09-03 at 4.27.19 PM (resized).png

A transformer can only input/output AC; the DC lines shown above are reference voltages that create an offset for the AC sine wave.

Did you measure the offset voltages coming out of the A2 power supply? Are the DC offset voltages correct and present at the transformer? If not, then the AC sine wave is not offset. However, for this to be the issue, both offset voltages would need to have a problem.

https://www.pinwiki.com/wiki/index.php/Gottlieb_System_80#What_is_the_DC_Offset_Voltage.3F

https://www.pinwiki.com/wiki/index.php/Gottlieb_System_80#System_80_.2F_80A_Power_Supply

If your A2 power supply is putting out all of the correct voltages at the test points, swapping it out seems pointless. Besides the MPU, what is common to all displays including the 4-digit? I looked at the ground schematic again and I was wrong, there are two different ground daisy chains. Most of the voltages are not shared across the 7-digit and 4-digit displays, except the 5 VDC.

If your display boards have all the correct voltages coming in, and they are grounded, and the MPU is good, they should be working. Did you verify all voltages on the power supply, including the pins and header connections? If your pin(s) are bad, a new power supply might exhibit the same problem.

I can't make any sense of it. Maybe somebody with more experience can glean a clue from that part where you can briefly see them light up on shutdown. Very weird.

How did this problem start? Was anything done to the game just prior?

Unfortunately, I am not surprised.

As per the System 80 Service Manual, kinda what I've been saying...

IMG_2750 (resized).JPG

There is nothing common to everything except the 60 volts at the A2 Power Supply and the MPU itself. I know I said forget the wiring, but this one is so weird I think you're going to have to physically verify every single wire and connection. Since you already tried a different MPU, maybe closely inspect the MPU connectors at J2 and J3.

You're welcome.

Assuming you were only reading voltages with the displays disconnected? Sometimes a weak connection will show good voltage until you put an electrical load onto it. It draws a lot more current than your meter, especially when the connection is loose; then the voltage drops, the current goes up and the connection gets hotter, which makes it even looser.

However, in order for this to affect all displays, you would need a couple simultaneous bad connections on the 60 volt pin, the 42 volt pin, and/or one/both of the ground pins, or some combination that works out. Wow... you really hit the jackpot on this one; go play the Lotto.

That J3 on A2 was one of the absolute worst connectors on my System 80. I ended up replacing all A2 headers and plugs entirely and switched them to the springy square style pins (Molex Trifurcon number 08-50-0189). I seem to remember that connector always preventing me from booting up for some reason... even though that problem should have been caused by J2.

I have seen this one before.

To add to this, note that most often you find 08-52-0113 contacts instead of 08-50-0189. They are the same thing except 08-50-0189 is brass, 08-52-0113 is phosphor bronze. The phosphor bronze contacts can withstand higher current loading.

I heard the square Trifurcon pins (08-50-0189) have better grab, but I did not realize the material was not as good. I imagine they're rated to be able to carry at least the same current as the largest wire size they're designed for, probably more.

Would it be better to keep the original style round (08-52-0113) or switch to Trifurcon (08-50-0189)?

Both 08-52-0113 and 08-50-0189 are trifurcon style contacts that are intended to work with square headers. The only difference is the material.
There is usually just a slight difference in price so most people just buy the 08-52-0113s.
E.g. Mouser list price in Qty of 100 -- 08-52-0113 = $10.20, 08-50-0189 = $9.20
When using the same 20AWG wire - 08-50-0189 is rated at 4.75A max, 08-52-0113 is rated at 6.25A max.
A third option is Molex contact 45570-3050 which is rated at 11.0A max with 20AWG wire but you must use 41695 series bodies (which can also use 08-52-0113). This one is pretty much overkill but works for connectors that tend to overheat. Real bugger to push on and pull off so don't use with larger pin counts.

The originals would have been closer to 08-52-0072 which is a flat style contact and was used for square pins, round pins and edge connectors. I use 08-52-0072 for Gottlieb edge connectors, 08-52-0113 everywhere else.

Thank you for the explanation. My notes are wrong because I thought 08-52-0113 was the original.

I think I got my Trifurcon headers and pins from a pinball supplier so just went with what they offered, which was the 08-50-0189.

Knowing more about these part numbers, I'll get from a generic supplier in the future.

Hopefully, this will be a moot point for my machine. Otherwise, I agree, the 08-52-0113 pins would be a lot better for practically the same price.