OSSC PRO settings for Atari 1040STe

[Retro-Computer-Shack]

Adjusting Analog sync made no difference.

[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.

[BuckoA51]

and is your system a ST with a RF modulator (composite video for sync) or without (composite sync) ?

[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 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]

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!).

[BuckoA51]

Rees did some beta testing on the OSSC Pro and his STe works with it – https://www.youtube.com/watch?v=4RJsdvM4fI4&t=877s

If you are willing can you remove the resistor from the composite video and see if that works?

[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.

[BuckoA51]

Can’t understand why it’s not working with your Pro when it did for Rees, very strange.

Should composite video be peaking that high? I guess Atari weren’t as careful as they should have been.

[Zacabeb]

The STe lineup was quite a significant hardware redesign from the ST and Mega ST (the latter already made changes such as including a blitter chip.) As Atari wanted to catch with the Amiga with the STe, they also wanted to challenge the Amiga’s reign as a cheap graphics system for community and local broadcast stations by including genlock support.

So, the STe likely outputs a more sensibly constructed video signal while the ST and Mega ST may have been a bit lenient in following specs.

[marqs]

I checked a few ST/STe schematics and it seems H+V sync is generated by GLUE chip. From there the signals go via a few basic logic ICs to MC1377 composite encoder and/or rudimentary sync combiner. Based on the reports it starts to look that only the RF-equipped systems which have MC1377 generated cvbs routed to AV connector are affected, but I’m still waiting some additional test results until concluding and considering next steps.

[Author]

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