Nanao (MS9?) sync issue maybe

[Tsukino]

A couple weeks ago I got an Astro City in that I had ordered from Yaton earlier this year. It had...well a ton of issues of course, but all things I expected and was prepared to slowly work on - awful control parts, rust removal, R/B convergence, hilariously bad reproduction side art, etc. The monitor was actually one of the best things about it, with very minor burn-in that isn't even noticeable except on pure white. Until it suddenly started having this problem yesterday:

It mostly rolls like that, which makes me think it's a sync problem, though sometimes it manages to hold onto the signal and create a more static image where you can clearly see each line just in the wrong place. I'm more than a little embarrassed that I don't know what this issue is, but I need some help figuring out what kind of problem it is and what I might try to fix it.

I assume I will need to dismantle the thing and take the monitor out, which I hate but have done before in the past. I was hoping people might have some suggestions on what to tackle once it's out though, so I only have to do it once. Looking from the rear access panel I can see at least one obvious thing, which is these potentiometers have something melted all over them:

I just have no clue if replacing the pots has anything to do with this sync issue. What else should I look at and maybe replace once I get the board out of there? Or am I just completely on the wrong track somehow? I'd also be happy to get someone else to fix the board if there are any suggestions for that in the US.

 

[rewrite]

It mostly rolls like that, which makes me think it's a sync problem, though sometimes it manages to hold onto the signal and create a more static image where you can clearly see each line just in the wrong place.

A video would be a lot easier to understand.

You're feeding it an actual signal and getting static plus rolling?

 

[Tsukino]

My apologies, it's difficult to get any sort of picture in my garage where it's at, and I'm not exactly a streamer or YouTuber, but I will attempt to get one uploaded somehow to better demonstrate what's happening.

The "static" or snow in that image is what I was sending it at the time, and is unrelated to the issue, again sorry for the confusion. Basically there are three things that can happen when I power things on:

1. It works totally fine. It did this for a couple weeks straight and still does it sometimes, but it seems to be increasingly less likely.
2. The picture is out of sync and constantly rolling, with the blanking intervals visible as in that photo. This is the most common, and what I'll try to get a video of.
3. After a while of 2 without sending a different signal (i.e. nothing with a different sample rate that would cause a re-sync) it will stop rolling and produce a static (lines stay put) image, with all the lines incorrectly placed across the screen. Unfortunately this is the least common so I'm unlikely to get a video of it. I attached a photo of the NEO-GEO startup screen from when it was doing this.

Garage is about to get too hot for me to work on it for the day here, but thank you for the response!

Edit: Oh and something I forgot - when it has the issue there is a high-pitched whine that can be heard coming from it somewhere. If the issue isn't there and the display is normal, then the whine is also not present.

 

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It works totally fine. It did this for a couple weeks straight and still does it sometimes, but it seems to be increasingly less likely.

I'd imagine knowing that it works fine sometimes you can assume it's cold solder joints somewhere, I'd just start touching up as many off-looking joints as you can find.

Reflow the sync/hold pots and spray them all with deoxit and work them back and forth while you're there too.

My apologies, it's difficult to get any sort of picture in my garage where it's at, and I'm not exactly a streamer or YouTuber, but I will attempt to get one uploaded somehow to better demonstrate what's happening.

Even a simply video with your phone would be useful. Doesn't need to be anything fancy.

 

[Tsukino]

I'd imagine knowing that it works fine sometimes you can assume it's cold solder joints somewhere, I'd just start touching up as many off-looking joints as you can find.

Reflow the sync/hold pots and spray them all with deoxit and work them back and forth while you're there too.

Oh that makes sense. Once I get the chassis out of there I'll start with that.

It's kind of funny/sad that I troubleshoot for a living and didn't even think to mention that sometimes it still works first.

Even a simply video with your phone would be useful. Doesn't need to be anything fancy.

Well, here we go then, quick vertical video of what should be Progear.