C-Sync on 520ST C070115 REV.2B

[exxos]

The caps on the sync lines are not always fitted. Normally there's caps on RGB signals as well. They are basically optional. They are there to clamp a bit of noise on the signals.

[exxos]

I also assume R131 output is actually connected to the csync pin on the monitor socket..

[spbmlb10]

Yeah I have checked the c-sync pinouts from R130 to Monitor Pin and it’s right. I also had a 1040 here that worked perfectly with it plugged in. Double check cable pinouts from the Commodore Monitor and it’s the same pin. I have a cheap oscilloscope here but havnt has much practice with it. Can I check the c-sync signal at all?

[spbmlb10]

Ok I tried something else, I realised the 1084s has v and h sync. Not sure why I didn’t try it sooner I have this picture coming up once creating a cable for v and h sync. I connected the c-sync circuit I created to correct c-sync pin later as well to see if things would change and nothing changed.

What I’m getting is the image now not rolling but i cannot adjust it any more to the left with monitor adjustment. Had no issue with 1080 on same monitor.

87756D79-F037-4F19-BB25-0DB17FA652F9.jpeg

I’m also getting some type of jumping. Cannot attach video very hard to see in it anyway. The top and bottom of screen are moving a few mm down then back up in a timed pattern it’s less than a second. I don’t know any other way to describe it. Refresh rate related? Or sync? I’m not sure.

Lol 😂 seriously this is taking some time to sort out but I’ve invested that much time now I’ve got to get it right. Any more ideas?

[spbmlb10]

Yeah I have checked the c-sync pinouts from R130 to Monitor Pin and it’s right. I also had a 1040 here that worked perfectly with it plugged in. Double check cable pinouts from the Commodore Monitor and it’s the same pin. I have a cheap oscilloscope here but havnt has much practice with it. Can I check the c-sync signal at all?

I made a typo, its supposed to say R131.

[exxos]

Have you considered the monitor just doesn't work with the ST ? You should try a TV with scart ..

Do monitors even use csync ? I thought they just took v&h directly..

[spbmlb10]

I actually hadn’t considered it. Due to having the 1040 working I thought it would have been possible. 1040 was running purely csync to monitor no V or H sync connected so it must accept Csync. Anyway if moving to the scart option and that was also my next step once I had it opersrional on the monitor I was under the understanding I would need the csync circuit working for scart sync to work or is there a way to use be v and h sync???


Cheers

Steve

Have you considered the monitor just doesn't work with the ST ? You should try a TV with scart ..

Do monitors even use csync ? I thought they just took v&h directly..

[exxos]

hmmm. . well I am no expert on monitors, normally just use V&H directly. Scart should be able to use either CSYNC or V&H sync... Though I can't say if all TV's or monitors will work with both methods.

CSYNC is just preferable for reducing some video artifacts. It may not even make any difference on some screens. In general its just done by default now I think. But its not actually needed.

[spbmlb10]

Sorry, I’ve been off the grid for a while, I had to put this project aside to get some sanity and now here I am back again.

I have worked out it is not the monitor but the Atari itself causing this weird issue. I have acquired a ST2VGA and on an older LCD monitor and my OSSC it still does the same thing. One thing I have discovered though that in High Res Monochrome the Atari screen is fine and tested on Atari High res monitor, my LCD and OSSC. It’s only in Color where the issue is. Here are new images through my projector using the ossc showing high res and colour and the same issue I’ve had all along with the green screen pushing right to he right of the screen and not being able to move it with any vertical adjustments... Any Ideas where to go from here?

119655BA-08EF-4A15-839A-D8CD54FC5047.jpeg

6AA5B59F-7316-4B31-9A39-631BA6EB1F4C.jpeg

E2BF27AA-29DE-431A-A003-44B71ADB3518.jpeg

7009C749-D5DF-4B00-B980-39D55F5E4427.jpeg

[spbmlb10]

Doing a bit more research could this be a problem with the shifter? I’m running out of options. ☹️