[Retro-Computer-Shack]

Removed the 150R resistor from pin 20 (start) and that works with the OSSC v1.8, but makes no difference with the Pro.

However without the resistor fitted this produces a voltage on pin 20 (sync) that peaks at times up to 1.24v which over spec for  both Scart and OSSC specs of 1V max, so not a design I would sell or recommend using, as this has the potential to damage the OSSC and other video converters, but won’t damage a TV with Scart input, as they can tolerate slightly higher voltages than the max.

AS my lead works perfectly with the OSSC v.1.6 and v1.7 with v0.90 FW, and all the other Video converters mentioned previously, then it’s just a timing issue, I’ll just have to spend so time experimenting with the v0.90 timings, and see if I can get it to work. Unfortunately I don’t have time to do that right now, but will let you know if I solve it.

Thanks for your help.

Ian.

[Retro-Computer-Shack]

Just tested using my Atari Mega ST2 , Which outputs a CSYNC (not CVBS) sync signal. This works perfectly using the same Atari ST RGB Scart lead, with both the OSSC Pro and OSSC v1.8 with v1.12 FW. produces a perfect rock steady picture.

So it would appear, that it just needs the correct settings to work with a CVBS sync (whatever those might be!).

[Retro-Computer-Shack]

Just to be clear, I’m testing with an OSSC v1.8 with v1.12 FW. Adjusting Analog Sync made no difference.
I’m testing with a 1040 STe which outputs Composite Video on pin 2, and so is using this for sync on pin 20 at the Scart end.

[Retro-Computer-Shack]

testing, with a 1040 STe which outputs composite video on pin 2.

[Retro-Computer-Shack]

Just to be clear I’m testing with the OSSC v1.8 with v1.12a FW. adjusting Analog Sync made no difference.

[Retro-Computer-Shack]

Adjusting Analog sync made no difference.

[Retro-Computer-Shack]

After speaking to Matt (and thanks again for you help). here is the problem.

I design make and sell and support video leads for Micro computers, and sell them worldwide.

My Atari ST and STe RGB Scart leads, work perfectly with the OSSC v1.6 and v1.7 using v0.90a firmware (but not with 1.x). They work perfectly with the RetroScaler GBSC Pro, with default settings, and work perfectly with the RetroTINK 5x with a few quick changes to the default settings. https://youtu.be/Ti_jpO9dKLo

They won’t work with properly with v1.8 OSSC with v0.90 firmware, get a stable picture most of the time, but intermittently get a blank “no signal” picture, and won’t work at all with v1.12 firmware, sync frequency reading on display go mad, changing all the time, occasionally displaying a picture for a second or so, but most of time nothing.

My Scart lead used Composite video for sync on pin 20 of the Scart connected via a 150R resistor, which together with the 75R input impedance (voltage divider) gives a voltage of about 800mV Peak, as measured with a scope.

Blanking signal is provided by the VSYNC signal from the ST connected directly to pin 16 on the Scart. RGB lines are connected with 150R resistors. I appreciate not many people will be using the OSSC with an Atari ST, but it would be nice to get working again, with an OSSC v1.8 with latest firmware.

Regards,
Ian Priddey (Retro Computer Shack).

[Author]

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