I'm a monitor idiot.

Finch

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Here's an amusing tale.

Recently repaired a G07. It's the first arcade monitor I've ever owned, it's the first monitor I've ever tried to repair and only really my second experience with using analog RGB+S hooked up to a CRT, so with very little experience I embarked on a full cab repair.

So I have the monitor working again, I turn the brightness up and I've got raster. I check B+ and get it adjusted to as close to 120v as I can get it. I look around for something to hook up in order to test this possibly working monitor. Consolized Neo Geo won't work because it has resistors on the RGB lines in order to hook up to my Sony PVM, so I go for my RGB modded Sega Genesis.

So I figure the Genesis is fine as it's the right resolution, it outputs RGB, and it works on the PVM. I hook it up and get crazy scrolling slanted image. WOW, something must not be adjusted right! I start tweaking knobs on the back of the chassis. Much tweaking of Vertical Hold gets something that looks like it might not be scrolling vertically anymore. So I start on H.FREQ next and I'm sitting there, arm in the cab trying to make the ABSOLUTE smallest adjustments possible to get the screen to not scroll horizontally. I feel like I'm getting close but every tiny indistinguishable little nudge on any pot is a world of difference and I can't get the damn picture to stay put. About this time I'm thinking anyone who tried to do this must be totally crazy. I have Sonic the Hedgehog screens slowly scrolling vertically and horizontally slowly across the screen....I'm annoyed.

Then I accidentally knock the sync line out of my little SCART adapter.....the screen is exactly the same. IT NEVER HAD A SYNC LINE. Now most of you would know this immediately.....but I've never done this before, so I had no idea what no sync signal looked like, and I just spent a good hour trying to get a clear picture out of a monitor with no sync signal.

I give in, Plug in the Neo Geo and turn off all the lights, sure enough, there's the crosshatch pattern, perfectly aligned and a small tap on V.HOLD gets it to stop jumping around and everything looks perfect (save for being very dim from the resistors on the RGB lines). I'm now thinking that the Genesis Syncs on green, and the PVM is smart enough to just pick this up where as the G07 isn't made for combined sync.

So I have a working monitor, and I feel like an idiot, but all is well as my monitor adjusting and repairing are done for this project and I can finally finish up everything else.
 
G07 will work with combined sync, as long as you connect it to both sync pins...
 
G07 will work with combined sync, as long as you connect it to both sync pins...

It wasn't that, the sync lines were already combined. It's that my little box I was using to run lines to the G07 took the sync line from a scart cable and used that for the G07. Turns out the Genesis doesn't use the sync line since it combines it with the green line. It works with the neogeo because it actually uses the sync line.

I just never noticed because my Sony PVM monitor autodetects sync and uses either.

I guess it might have worked if I jumpered the green to the sync line, but who knows if the G07 would figure that out.
 
I have Sega Genesis modified for jamma cabinet. Now on my SNK Neo29 cabinet I just used sync from Genesis, but when I tried in my Sega Astro City it would get wavy lines. Added LM1881 (see gamesx.com) sync cleaner, please note input is composite video to this circuit and all works great. I think sync out of Genesis was a little off. Hope this helps.
 
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