MS8-29FSG maximum vertical size issue

[csonesz003]

Hey there!

Looking for some help. I have a sega Astro City 2, that is not getting a full vertical picture. Looks like maybe half inch of picture is missing from top and bottom of screen. Tried adjusting the vertical size and position pots with no luck, this is the max that I can get. I just installed cap kit and it was working well, got the full size. Recently started to put things together after a deep clean and restoration, but turned out it’s not ready. I measured the pot on the remote board and got 500 ohms which is expected. The chassis is a Nanao MS8-29FSG. Could you please help me what can be the culprit or where to start?

 

[ner38073]

Hi. The cap kit won't solve this issue. I'd first do a reflow on the entire vertical section. Cold solder joints might be causing this.

 

[csonesz003]

I already checked and also changed some of them but didn’t help. Which components can cause similar issues to this?

 

[ner38073]

I already checked and also changed some of them but didn’t help. Which components can cause similar issues to this?

I would then focus on the horizontal pots. Replace them. Do they have a reading or label on it? Aftermarket won't be the same look but will still work.

 

[csonesz003]

I tried with a donor remote, but same behavior. Already changed Q401, Q402, IC401, D530 as I read these are common issues. Also reflowed the remote connector pins and several other vertical parts that I could find. The main issue is that I don’t really know what are the exact vertical components :/

 

[ner38073]

Does it happen with all games? Reflow flyback and all neckboard. Then proceed with replacing the vertical size pots.

 

[csonesz003]

Yep, it happens with all games except M72 boards, but those are known to run with an unusually large vertical size. I also tried a different remote board and the behavior was exactly the same, so we can rule that out.

I reflowed most of the components in the vertical section on the main chassis, based on this schematic from Franck78

https://github.com/Franck78/NANAO-MS8_29/blob/main/nanao-ms8-29.pdf

The flyback has already been reflowed, and I also reflowed the transistors on the neckboard.

Which parts dhould I reflow? This schematic is a bit hard to read.

 

[ner38073]

Was everything working fine before or that is how you got the monitor or chassis? The issue is evenly on top and bottom. The problem should be on the vertical section. Inspect all solder joints. I have a feeling a trace to the vertical IC is cold. If nothing works, proceed to replace that IC.

 

[csonesz003]

I reflowed the whole vertical section and changed the vertical IC. It was working a month ago. Just disassembled for dust cleaning and now this is the behavior.

 

[ner38073]

You might have hit a component while at it. Some old devices work good in their original state, even if they are all dirty and nasty. When you alter their old dirty they start acting out. Next try to recap the vertical section but we might want to first try to replace the 1 or 2 capacitors in the power supply section that lead to the vertical section. That will be a good next step. If you feel like giving up send the chassis to Jhon at PNL. He will fix it if you are in the States.