Stargate Power Supply

rlinsky

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I'm trying to determine why my new Stargate machine is not working. The marquee lights up, but that's about it. Nothing on the monitor, no sound. I don't have any number showing up on the main board. I only have 2 LEDs lit, the bottom two. I will post a picture of the power supply. What's the next step? I suspect I need to rebuild the PS board, but how do I determine whether it might be the transformer output instead? Or perhaps the connections between the two. I have a multimeter, but I'm not sure exactly how to test it. I am a beginner.
 

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The diagram shows the lower part of the power board in Stargate. Connector J1 is where the AC from the transformer comes into the power board. Set your meter to AC and test all the voltages coming in. For instance, one lead on pin 11 and the other on pin 12 should give you a reading close to 11.5 volts. Being AC it doesn't matter which lead goes on which pin. Go down the connector and compare the voltage readings you get with the drawing.
 
When your game is powered on, you should see 3 LEDs lit on the power supply board.

If any one of those LEDs are out or dim, your Stargate will not boot. It needs all 3 voltages to run (+5v, +12v & -5v). The best place to test the voltages are on the corner legs of the memory chips (4116) with a multimeter.

Also, reseat all of your connectors that supply power to the boards (MPU, ROM, & Sound) as well as the ribbon cable to the ROM board. I like to clean the header pins with a green 3M scotch brite pad to remove any corrosion as these games are 30+ years old and usually have some corrosion on the pins!

Keep us posted on your progress.
 
Ditto what he said. But it never hurts to check the voltages from the beginning as you have asked. I would check the voltages with the connector plugged into the board as they could be a bit lower with a load on them.
 
Connector is different

I went to measure the voltages, but my connector doesn't prelate directly with the schematic. Mine has a total of 10 wires, not 7 as in the picture. I think I'm going to send it off to Dokert to fix it, but I'm trying to learn a little in the process.

Here's an image of the connector.
 

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Does your game have the drawing on the back door still staples to it? Compare that if it's still there.
 
It looks like someone at one point upgraded your Williams power supply to the Joust/Robotron power supply. That's fine. (Stargate originally had a different type of power supply with the Heat Sink mounted directly on the board itself.)

The 15-pin connector that you show matches up to the wiring diagram except for the last few wires on pins 14 & 15. They are the 6.3v for the coin door.

Also, did you check the Main fuse by the transformer?

When checking fuses (with power off of course) pull them out of the holder, one at a time and test them for continuity. If you test them in the fuseholder, you could get a false reading. Also, make sure that you have the correct fuses in the power supply.

So, do any of the power LED's light up on the power supply?
 
Kinda on topic... does anyone know what exactly controls +5 volts on these power supplies, I rebuilt one for a Joust and it's still showing low volts on that, like 4.4v. I saw something in the manual about changing a resistor to either raise or lower that voltage, but wondering if it's a transistor or something else that needs replaced. I used Bob's rebuild kit with new caps and voltage regulator ic's along with the motorola transistor for the heatsink.
 
Voltage measurements

Ok, so I found a schematic of the Robotron-style power supply. I then made some measurements. I don't really understand the concept behind what I'm doing here. I figured I would just be comparing everything to a common "ground" voltage, but that doesn't seem to be the case. Can anyone explain why I'm doing it this way? Is this even right?

Yellow to White/Yellow=6.8VAC (6.3 on schematic)
Orange to Violet/Yellow= 9.1VAC (11.5 on schematic)
Gray/White to Gray/Yellow=26.6VAC (20V on schematic)

I wasn't exactly sure how to measure single wires, so I measured the following combinations, not sure how to measure these properly:

Green to Black=10.6VAC
Green to Gray/Green= 10.6VAC
Gray/Green to Black=21.3VAC
Green to Gray/Yellow=0.6VAC
Green to Gray/White=1.8VAC

Just trying to make some sense of it all without having to become an electrical engineer.
 

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Kinda on topic... does anyone know what exactly controls +5 volts on these power supplies, I rebuilt one for a Joust and it's still showing low volts on that, like 4.4v. I saw something in the manual about changing a resistor to either raise or lower that voltage, but wondering if it's a transistor or something else that needs replaced. I used Bob's rebuild kit with new caps and voltage regulator ic's along with the motorola transistor for the heatsink.

Yes, I do. You did not change the 18K cap now did you? Biggest cap on the power supply. Most people make the mistake of not changing the 18K cap, and then wonder why their +5vdc still has problems. The LM723 controls the +5vdc, along with the resistors within its circuit. Removing R10 will increase your voltage, but in your case probably not enough.

Ok, so I found a schematic of the Robotron-style power supply. I then made some measurements. I don't really understand the concept behind what I'm doing here. I figured I would just be comparing everything to a common "ground" voltage, but that doesn't seem to be the case. Can anyone explain why I'm doing it this way? Is this even right?

Yellow to White/Yellow=6.8VAC (6.3 on schematic)
Orange to Violet/Yellow= 9.1VAC (11.5 on schematic)
Gray/White to Gray/Yellow=26.6VAC (20V on schematic)

I wasn't exactly sure how to measure single wires, so I measured the following combinations, not sure how to measure these properly:

Green to Black=10.6VAC
Green to Gray/Green= 10.6VAC
Gray/Green to Black=21.3VAC
Green to Gray/Yellow=0.6VAC
Green to Gray/White=1.8VAC

Just trying to make some sense of it all without having to become an electrical engineer.

Your problem has nothing to do with 4P1, in this particular case. Your problem is with the power supply itself.

Yes, I made sure all fuses had continuity. Not sure exactly how to tell if I have the right ones. Are the direction-specific?

They are listed in the illustrated parts breakdown in the manual.
 
Yes, I do. You did not change the 18K cap now did you? Biggest cap on the power supply. Most people make the mistake of not changing the 18K cap, and then wonder why their +5vdc still has problems. The LM723 controls the +5vdc, along with the resistors within its circuit. Removing R10 will increase your voltage, but in your case probably not enough.

Thanks Dokert, I thought that might be the issue... I did replace it, however only temporarily to test using a pull from another board. It's probably not up to par since it was older. I'll throw in a new fresh one.
 
"Power supply itself"= transformer, etc?

Forgive my ignorance, but what is "4P1"? Is that the name of the Power supply board? Are you saying the problem is "upstream" from there, in the transformer thing on the floor of the cabinet? How can you tell? Is this fixable? Replaceable?

I don't yet own a manual, didn't come with the game. I'll try to track down one online.
 
Send it in to Dokert if you don't feel comfortable working on electronics.
You are most likely looking at replacing Capacitors and some LM723 chips.
 
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Forgive my ignorance, but what is "4P1"? Is that the name of the Power supply board? Are you saying the problem is "upstream" from there, in the transformer thing on the floor of the cabinet? How can you tell? Is this fixable? Replaceable?

I don't yet own a manual, didn't come with the game. I'll try to track down one online.

This is 4P1...

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The problem is actually downstream. I have repaired hundreds of Williams power supplies and power bricks. Yes, it is fixable.
 
Forgive my ignorance, but what is "4P1"? Is that the name of the Power supply board? Are you saying the problem is "upstream" from there, in the transformer thing on the floor of the cabinet? How can you tell? Is this fixable? Replaceable?

I don't yet own a manual, didn't come with the game. I'll try to track down one online.

http://arcarc.xmission.com/PDF_Arcade_Williams/Stargate_Drawing_Set_(16P-3002-103)_Dec_1981.pdf

try that, might be what you're looking for.
 
From the description of the problem, it was needed. Hopefully this will be the only issue in the game.

Just remember any time you work on a game always start with the power. Without good power you can't properly trouble shoot anything else.
 
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