JAMMA power supply ground

smonroe

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Have a standard power supply with 2 boards hooked to it (it's a Nintendo Red Tent). When one monitor is plugged in (regardless of side) everything works. When both are plugged in, the graphics pulsate on both sides. I've ruled out monitor power so I'm down to overall power orgrounding. I have the supply wired into the original Nintendo supply. Should I get a separate power wire do the supply runs on its own line? In regards to the ground, both pcbs grounds go to the power supply and I have the ground from the supply going to a screw on the plate across from the Nintendos power supply ground. Is that where it should be connected? Am I missing something?
 
It's called a ground loop, its the nightmare of all things electronic.

The issue comes back to you running everything off one supply but multiple ground connections. Sadly the only thing you can do is try to reduce everything back to a star network. Make everything ground ONLY back at the power supply.
 
You have two different Jamma boards in it, correct?

If so, your problem is the two boards are running at different frequencies. The monitors in a red tent are so close to each other that they are interfering with each other.
 
I found a thread from 2014 talking about this issue in a standard cab. They concluded to either dump the monitor grounds or dump the FG on the power supply or put a wire between the FG and regular ground. Thoughts?
 
Its possible that the sync frequencies are causing problems. And its very likely its a ground loop problem. The only way to find out would be to power the games on and play with the sync pots on one of the monitors and see if anything changes. Thats what I would do anyways.
 
If your cables are long enough so that you can take one monitor out and still run it then you'll be able to tell that it is interference. I'm not sure how much of an affect the sync pot will have as the two boards are likely running at 2 different frequencies and resolutions.
 
because the the most likely interference frequency is going to be the hsync frequency. Which if you have ever used an oscope near an active monitor you will know what i'm talking about.

Change the hsync frequency you can change the beat frequency of interference on the second monitor.
 
You have two different Jamma boards in it, correct?

If so, your problem is the two boards are running at different frequencies. The monitors in a red tent are so close to each other that they are interfering with each other.

so is that weird ghost hum bar thing on those normal then? (when running all original Vs. hardware)
 
so is that weird ghost hum bar thing on those normal then? (when running all original Vs. hardware)

Probably. I don't have mine hooked up as a VS on both sides atm to verify what you are talking about. In this case, both "games" are using the same crystal to drive both monitors. You may notice slight dimming etc from interference when the monitor on one side has a dramatic screen change.

If you have a Playchoice on one side and the VS on the other, you may see a slight hum bar as well that slowly rolls. Both games use the same value crystal, same resolution etc. You can kinda try to get the hum bar to stop rolling if you adjust the Sync pot since the resolutions of both games are so close to each other.
 
yeah, I think my monitors are probably all original, was wondering if that's how they were or if they needed some serious cap and reflow attention. I had to change a yoke on one of them, convergence needs help too. what a debacle.
 
Change the hsync frequency you can change the beat frequency of interference on the second monitor.



Did a test where I pulled one monitor out and sat it on a stool. Both sides worked perfect. Next I propped it on the frame without dipping into the machine. No waves. Then I angled it down toward the other monitor and the mounting bracket. The waves began.

So... Not a ground issue. Not a power issue. but interference. I'm assuming I adjust the HSYNC on each monitor. I'm not familiar with adjusting this on xm1801s any advice? Both sides or just one?
 
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