Supergrafx RGB Image Shearing

[famiac]

Hi all.

I modified my SGX using the amp on the gamesx website. Much like Chris Covell, i experienced image shearing after the initial mod, but only on my BVM 20F1U. I removed the amplifier as Chris suggested here, but i'm still getting the same problem.

Any idea what might be causing this?

[thesteve]

your monitor is expecting C-Sync and your feeding it composite video instead

[famiac]

I'm pretty sure, if not positive, that i tapped the signal from the correct c-sync pin. Also, my pvm, which does display the image properly, would not display it if i was actually feeding it composite video. I will double check, though.

Thanks for the tip. I'll open it over the weekend. My gamebit is at my parents' house.

[K-2]

Have you properly terminated the BVM'S outputs with 75ohm BNC terminals?

I have the same monitor and I had to do it to get my Duo to work.

You can find them on Ebay, just make sure they are actual 75 ohm BNC terminal caps and not just dust covers. Hope this helps

[thesteve]

its also possible that your sync is just too low

[Vimtoman]

It's definitely Sync tearing. Try placing a cap in series with the C-sync signal. Try a 220uf .

[famiac]

Ok. I will try all of your suggestions. I bought some 75 ohm terminators. I only have one right now.

Thanks guys

[famiac]

Ok, so it's definitely connected to c-sync.

I added a 220uf cap in series. I'll report back tomorrow to see if it worked.

[thesteve]

remember the 6260 only puts out 0.3V sync which doesnt make most displays happy

[famiac]

The sync was amplified, but i disconnected the amp after i saw the image shearing because that's how chris covell got his to work. It was part of the trial & error process. I could reconnect it.

[thesteve]

the amp i suspect you used would not have produced any voltage gain
the easiest way to deal with it is using the LM1881 from composite video

[Vimtoman]

The image may shift if using the LM1881.

[famiac]

Ok, i've tried adding the 220uf cap and terminating the outputs. None of those worked, so i'm gonna try the lm1881 as a last resort.

[Vimtoman]

0.3v is the standard level for the sync pulse.
Have you tried the sync pulse direct from the expansion port via a capacitor?
Not through the amp.

[famiac]

Yeah. That's how it's configured right now