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JPAC Video Issue


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Hello Everyone

 

My MAME cab has always been very hard to look at, the image is really unstable and has a sort of horizontal gitter to it. I always thought my chassis just needed a service but then I connected an MVS with Metal Slug X and the picture is really stable. I'm using a HD5450 with CRT Emudriver installed and a JPAC into the Astrocity cab.

I've made a comparison video, the focus is a bit dodgy but you can see what I'm talking about. https://drive.google.com/file/d/1arhz3nwz2x3JenxZBZ0DQV25MXm_5Kp4/view?usp=sharing

Would love to know how to fix this if anyone has any ideas.

 

Cheers, Ben

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Groovymame is awesome but it can be a very complicated beast to get set up right, I'm running the same set up as you and my Astro's look great, I'm far from an expert but I would guess that you might have some shielding issues from the video output cable from your PC maybe?

 

I bought a shielded cable and it was a great improvement for one of my cabs.

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I had considered that, I'm only using the flimsy little VGA cable that was provided with the JPAC. I have gone to replace it once before only to realise it's a male-female cable and I've been too cheap to buy a good one to test with. And just now, while I am typing this post the solution came to me.

IMG_20190415_233808.thumb.jpeg.71b3e4e06bfc1b50f54c2b06e80f3db6.jpeg

 

Sent from my Nexus 9 using Aussie Arcade mobile app

Edited by Rustler77
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Do you have that motherboard mounted in the cab without a case? Perhaps the PC is picking up interference from within the cab or power supply? Can you run the PC outside the cab and plug it into a different power point to the cab?

I leave my PCs in cases behind my cabs for easy access.

Not as pro but you don't see them while playing.

 

Sent from my SM-G920I using Aussie Arcade mobile app

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Hey Rat

 

Its been setup externally and on a different power supply while I've been trouble shooting and its made no difference.

 

I started this post on ArcadeControls and someone there is suggesting that I adjust the sync pot on the chassis. I didn't realize that was some thing that needs to be done when swapping out PCB's. Its a bit of a mission to get to the back of my cab but I'll give it a go I guess?

Edited by Rustler77
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I just run my cabs with PCs and don't swap out boards so I have no experience with sync issues when doing that, but it's easy enough to mark your pot and take a picture of it so you can return it if needed then carefully adjust and see if you can get it looking better. Sometimes these old pots can break when adjusting them, but I have adjusted pots in both my cabs and not broken one.

 

If that doesn't work then I suggest showing your video to Jomac as he will know what's going on and what to do about it.

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It was suggested to someone on a different forum with a similar sounding problem that the MAME PC needs to be grounded to the JAMMA harness. I'm in Australia so my Astrocity has been fitted with a 240-110V step-down transformer and my MAME PC gets power from the back of the cab before it hits the step-down.

 

Also, sometimes I get a decent tingle from the JAMMA harness or the ground shields of things connected to it. I might have a bit of an earth leak or something, not sure if this would have anything to do with my video problem?

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Had my electrician brother and his multimeter around over the weekend. He pointed out that the power supply in my Astrocity wasn't grounded at all and that there was a 75V voltage drift between the mains ground at the back of the cab and the Jamma harness ground. Shouldn't the AC100V in and the DC out to the JAMMA harness have a common ground to stop this voltage drift?
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  • 2 months later...

Long overdue update

 

Shortly after my last post the picture on my Astro City started surging and eventually got to the point where it faded out to a black screen and didn't come back. So I sent the chassis off to @Jomac for a service. When it came back it was working about the same as it had been before it started surging, still had the high pitch squeal noise and it still had the jittery graphical issue that has haunted me for years. So I gave Jomac a call and he suggested the squealing noise might be caused by a failing step down transformer so I plugged in a spare one that I had for a US N64 console. Instantly all the noise coming from the cab disappeared and the graphics were perfect, everything I’d ever hoped for. The edges were stable and the whole image was rock solid. Happy as a pig in mud I went and had dinner with my family but when I came back 15 minutes later the picture had started surging again, so back to Jomac. While the chassis was away I replaced the temporary transformer with the brand new toroidal transformer. A few days later the chassis was back at no extra charge and the surging was fixed. I fitted the chassis to the tube, plugged everything in externally and tested with my MVS hardware. Now I'm presented with an entirely new graphical issue, the picture is still solid and sharp but I have a ripple effect rolling across the screen at a 45 degree angle. I soon figured out that grounding the jamma harness to the back of the cabinet fixes this new issue. The color is a bit washed out so I move on to adjusting the flyback, brightness and color pots and now the picture looks better than it ever has before. After playing Metal Slug 3 for about an hour I'm really happy with the results and power everything down and fit the tube and chassis back into the Astro City. I power everything up again only to find that I'm getting a new humming noise from the neck board that changes in time with the graphics and a graphical issue very similar but different to the original problem. Its at this point that I spit the goo, turn the machine off and not look at it for six weeks.

Today before writing this post I thought I'd turn it on to see if it was behaving, it blew the main fuse and didn’t turn on.

I think I can safely say my issues are not related to the jpac.

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  • 1 month later...

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