30 Hz Midway Flicker--Can it be helped?

supertechnoboy

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I have always had an issue on my Rampage that I would describe as a jittery, jumpy, or flickering in the vertical direction. It seems like it jumps up and down by maybe a scan line, at a fairly high frequency, and it does it all the time. I tried to record a video with my phone, but the condition is not visible when recorded. I have a K4900 in there now, but the problem also existed with the previous monitor.

I had assumed it was 60 Hz AC getting in through the hacked-in switcher. I was able to find a broken original switcher, repair it, un-hack and re-pin the harness, and reinstall. The problem was identical. The monitor had already been recapped, but I replaced the big filter cap just for good measure (no change). I also checked B+ (right on at 129.9V).

Next I eliminated environmental factors. I unhooked the marquee, turned off all the other machines and lights, and put Rampage on it's own circuit. Same damn thing. So then I remember that Spy Hunter also does this, and Tron too. I thought maybe it was and MCR thing, but now I'm thinking it's a Midway thing. But not so fast, Ms. Pac is rock solid. So what the hell's going on?

The only thing that I've found is that Tron, Spy Hunter, and Rampage all run at 30 Hz refresh rate. Everything else I have (that works) runs at 60 Hz, and looks terrific. So, to finally reach my question, is the flicker from the 30 Hz refresh, and if so, can I do anything about it?

EDIT: It is an MCR thing. Rampage is MCR monoboard.
 
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They may only run at 30fps, but I think you'll find that they do run at 60hz.
I was basing my 30Hz claim off the MAME data. Is this because the video is interlaced? If so, that would explain why the effect is most noticeable on the thin white horizontal window ledges. That would be a pretty bad scenario for interlacing.
 
I just noticed this on MAME when I was setting up Tapper and I was utterly confused -- the resolution is far beyond the normal CGA resolution and yet it was working fine on a standard res monitor.

Someone told me that the 30hz was so that it could draw the higher resolutions.

There was no 30hz option in MAME for the monitor so I'm not sure what I'm missing.

I too noticed that my text was slightly jumpy on Spy Hunter sometimes but I was never sure why... this may be the reason....
 
I verified through Midway's MCR documentation that the video is definitely interlaced, which is why it can run the higher resolution. So, what can we do? I still feel like the vertical sync could be better.
 
Interlacing shimmer cannot be helped sadly :/ this only became a bigger problem in the 90s as boards using custom ICs ripped from game consoles became popular, when these ICs brought their 480i native resolution with them. It's only finally disappearing now as companies shift to PC-based hardware driving LCDs at wicked high (and progressive) resolutions.

There's the occasional case where the board can be modified to output VGA instead, but that also means finding a different monitor unless you're lucky enough to have a suitable multisync already in the cabinet.
 
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