When you put a load on the line, there will always be a voltage drop--not usually quite that much, though (usually it only drops about 0.1v to 0.3v). In any case, take a multimeter and measure the voltage on the MPU and then adjust the POT on the power supply until the MPU gets 5v.

Have you done any work on the power supply?

The same advice applies if there is a POT adjustment, but I'm not familiar with those replacement boards. You might have to contact Frett Swemmer directly for support on those.

I'd try powering the MPU on the bench, with a PC power supply, and read the voltage drop. If it powers up, stays around 5v, and doesn't shut down the PC power supply, then I'd suspect the power supply board.

It could be a short on any one of the chips on the MPU. Do any feel hotter than the rest? I can't remember if the 6532s run a little hot any way, perhaps someone can chime in.

Just because it is brand new doesn't mean it doesn't have a defective component.☺

No, there should not be a 0.7v drop on the 5v supply. There is a component on either the PSB or MPU that is bad. Do you have access to any other working boards compare?

Have you contacted the manufacturer for advice?

if the wire has come off the 8v + bridge you will loose power

First, don't connect or disconnect displays with the power on. This includes J2 and J3 on the MPU. Doing so will fry the 7448 display drivers on the MPU.

With power off, disconnect display connectors for player 2 and player 4. Power on. Measure your 5V.
Power off, reconnect player 4. Power on. Measure your 5V.
Power off, reconnect player 2. Power on. Measure your 5V.

Report results.
Don't worry about the chaser lamps. Let's get the 5V fixed first.

BTW, there is a System 80 section in the PinWiki.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info

The Swemmer power board is more or less a direct copy of the original. It has a voltage adjustment on the board. Might just need adjusting.

http://www.pinwiki.com/wiki/index.php?title=general#Testing_a_Bridge_Rectifier

What is "correct power"?

Anyway, if you want to check voltage at some point, voltage is potential so use a multimeter (set to DC/AC volts) and stick one probe on the point you want to test and the other probe on an appropriate ground point. Be careful.

Just curious, when you are testing your power supply board voltages, what are you using for your ground point?

Voltage is potential between a point and some reference. What you use as reference depends on AC/DC and what you are testing. For example if you were testing the AC voltage going into the line filter, you would check between the line and neutral to read ~120V.

Perhaps someone will write the tutorial you are demanding. Good luck!

Perhaps the connotation or phrasing is what led radium to think more in terms of "demanding" vs "asking".
The written word loses so much over personal face-to-face comms.

This isn't the answer to your question, but the way you'd like to go is hardly ever necessary. If you measure the spec AC voltage into the bridge, and the spec DC voltage out of the bridge, that eliminates the need for upstream measurements. The only power measurement left is to measure the AC ripple component of the DC power, which should be next to zero if the filter cap is doing it's job.

So, find a bridge.
Power on.
Red lead on one AC spade (marked with a ~). Black lead on the other (catercorner). Since we are measuring AC, orientation does not matter.
If the AC voltage measures close to the spec voltage (see the manual), that's good enough. It doesn't have to be right on.

Now, set your meter to DC voltage. Black lead on the spade marked with a minus symbol. Red lead on the catercorner spade marked with a + symbol. The DC voltage will be close to the AC voltage input * .812. That is the "perfect" rectification yield for a bridge. In practice, there is no perfect. Expect the measurement to be close.

To measure AC ripple, set your meter to AC volts. Black lead on ground. Red lead on the rectified and filtered voltage, like the 5V TP on the PS (which has also been regulated to about 5V). The AC component of that DC power should be millivolts only.

Make sense?
We're here to help.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info

BTW...you'll always know which lug is ground in a Gottlieb game as they consistently used a green wire with a yellow tracer across the manufacture of at least System 80 games.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info

None of those voltages are the problem.
I really, really think you have a shorted IC on either the player 2 or player 4 display. Hence the suggestion above.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info

Listen to Chris. The displays use 5VDC for their logic power.

Also note that bad displays can cause damage to your new boards. Heed the warning Do Not disconnect displays with the power on or you will cause damage. In fact do not remove any cables with the power on.

Your player one display may have a problem. Swap player 1 with player 3 display.

Determine which display is causing the power drop -- player 2 or 4. Try the good one in the player 1 position.

Ignoring the player 1 and 3 displays, with player 2 and 4 displays unplugged does the game go into the attract mode where the controlled lamps are sequencing on the playfield?

There is a diode test you can use, but personally, I haven't had success with it. If I suspect a bad IC, I put in a replacement. Although, with voltage issues on those displays, I've been finding that sometimes the resistors fail under load.

However--if all 5 displays are unplugged and you're still getting the voltage drop, the problem probably isn't the displays themselves.

You say that the voltage drop doesn't start until A1J2 is plugged in. Looking at the manual, A1J2 shouldn't carry 5VDC to the displays, just segment signals unless an IC is shorted out. Normally, with that connector unplugged, you shouldn't see anything in any of the displays. Plugging the A1J2 connector back causes the 5VDC short conflict.

I see this was suggested at the beginning of this thread but I didn't see where it was addressed. I know this has one of those "new" CPU boards in it but have you tried running it in a different game (since you've owned it) to see if the problem is in the CPU board itself? I understand that Fred always tests and videos his boards to prove they work, that's smart business and verifies that the problem is elsewhere.

However, it may be that a unknown existing display issue shorted out something on the new board when you plugged it in and turned it on the first time. This isn't that uncommon as anyone that fixes boards can tell you, even Fred knows this. I always tell anyone I fix boards for that once the board is plugged in and the game turned on, the board can short out again if the cause of the problem isn't corrected too. It may be the same issue that took out the original CPU board and the reason it was replaced by you.

My suggestion would be to send the board back to Fred for testing and have him repair it for you if needed. If it turns out that there is a problem, then, he'll be able to tell you where to look in your game to correct it. Then, don't plug the board back in until you do. If it turns out that the CPU board is good, all you've lost at this point is shipping costs and you're back to looking around for the issue again.

Steve
System 80, not just a job, it's an adventure

Just re-read the thread, was looking for clues and found this piece of info. If "none" of the displays are plugged in, then it should be the same as not having A1J2 plugged in even when it is. There would be no display load or short at all. Please verify wire color positions are correct at the credit display A5J1 since it's the only display that is supplied 5VDC in a 6 digit game.

Steve
System 80, not just a job, it's an adventure

Sorry, forgot to mention checking the other plug A10P5/J5. Make sure the wire colors going into the plug and coming out match. The reason I mention this is because I shot myself in the a$$ a few years ago with my MGoW's and caused a problem that took forever to figure out. I had two of them at one time and decided to sell one. I had one with a real nice playfield and one with a worn out one. Fortunately, I also had a NOS playfield so I decided to sell the more common red cabinet and keep the rarer black one. I swapped the red cabinet playfield out and put in the nicer one to make it an easy sale. At the time, I remember that I had to move some wires around at those plugs because the status display wouldn't work right no matter how many others I swapped into it. I assumed that all MGoW wiring would be the same and it wasn't. If the playfield had been swapped to a different one in your game, it's another "shot in the dark" but worth a look. If it happened to mine, unless you know your games history, it may have also happened to yours?

Steve
System 80, not just a job, it's a adventure

It's possible that a wire is pinching against something, then shifted as the game was opened and closed, causing a ground short. This happens a lot with the coin door wiring. I would think that with the connectors all disconnected, it would be possible to use a meter on the main 5VDC and ground lines to see if any are touching each other. Unfortunately, this problem is a tough one to diagnose without seeing it first hand. Right now, I'm grasping for anything I can think of. I'm not one to give up on a System 80 issue but I'm running out of ideas that might cause what you see. Question, did you look inside each connector you worked on to be sure there wasn't a piece of a crimp left behind and causing the new crimps to jumper to each other?

Steve
System 80, not just a job, it's an adventure