Sega Astro City - Nanao MS8-29FSG Pincushion problems with IGS board

[christian776]

Hi all,

I'm having issues with the SPC control, and the Horizontal Limit potentiometer, because in IGS games (EspGaluda in his case) the image size is doesn't fully cover the vertical space, so while I've managed to do so, the image is very curved on the bottom and top of the screen (well, actually the left and right side, since I have the monitor in TATE orientation). I'll appreciate any help.

 

[nem]

Adjusting S.P.C. doesn't straighten it?

 

[christian776]

I actually don't know why I didn't try to move the SPC potentiometer a bit more, it works, but, unfortunately it also deforms the image by shrinking the left side of the screen, seems like a trapezoid control should be what I'm looking for, but not exactly sure if the MS8-29FSG has it.

 

[nem]

MS8-29 has trapezoid adjustment. It's on the upright daughter card. Look for VR1, the small pot with a metal contact.

 

[christian776]

I was able to locate VR1 and try to fix the trapezoid issue, but at the expense of making the picushion re-appear, and trying to move the SPC pot deforms the image only on the left side, do you think it's fair to say that this is acceptable or perhaps I should check caps (or transistors) to improve image geometry?

 

[nem]

You'll often have to make a compromise. Corners can be fixed with yoke strips, but doing it is kind of a pain in the ass.

Certainly looks better than before!

 

[Mukuro_W]

There is a small pcb vertically mounted just in front of the pin amp ic , you will find a trimmer for trapezoid on this pcb.
Just remove this and check for broken solder joints on any pins .

 

[christian776]

Hi ! Yeah, I think you mean this one right?

 

[christian776]

it also looks like somebody did a poor job repairing this board. I wonder if I could use an MS8-26 schematic to guide me here.

 

[Mukuro_W]

Hi ! Yeah, I think you mean this one right?

And yes it is, just desolder and detach this board and inspect the connector for broken joints.

 

[Mukuro_W]

it also looks like somebody did a poor job repairing this board. I wonder if I could use an MS8-26 schematic to guide me here.

This is the V out ic LA7832, the worst job ever made there... Yaton style?

 

[christian776]

I ended up repairing those cold solder joints and measured continuity and is OK. I didn't desolder VR1 yet, I mean, it actually works, but when reaching the max value of the pot, the image still isn't perfect. Do you think this can related to poor soldering or maybe it's a transistor that is not being able to push it further?