OSSC PRO settings for Atari 1040STe

[Felipe Rios]

I have the OSSC v1 and recently purchased the OSSC PRO (both from VGP).  The OSSC worked out of the box with my ATARI ST, the PRO does not.  It tries forever to sync and it is unable to get a lock. I tried all modes and tried adjusting some of the settings based on the original OSSC, but nothing works.

Does anyone use the PRO with an ATARI ST that can share any custom settings?  Or maybe my OSSC PRO is defective and I should send it back.

Thanks!

Fell

• This topic was modified 8 months, 1 week ago by Felipe Rios.

[marqs]

I’m not aware of anyone having tried Atari ST(e) with Pro, but some time ago I debugged one 7800 that didn’t sync. In that case the reason was cable, or fundamentally bad design from Atari. Essentially pin 2 of the AV connector carries either composite video or TTL composite sync depending on the model. If you happen to have RGB cable designed for the other sync circuit type, you may end up with sync level which is either too weak or high enough to potentially damage modern receivers. If the cable is suitable, you could try adjusting Analog sync Vth on Pro’s sync menu (although this should not be needed if sync level is right).

[Felipe Rios]

Thanks for the reply.  I tried a VGA cable that works fine with the OSSC but didn’t work with the PRO.   Then I tried another SCART cable and had the same issue, but I changed LPF to (2.5) and the Atari GEM screen appeared but rolling vertically!   I have no idea what to change to make it stable.

The PRO works with my other computers without any adjustments just like the original OSSC.   It’s the weird ATARI ST video output that the PRO is no longer able to handle.   If there is no settings fix, I will continue using the OSSC and use the PRO just for the C128 and Apple IIGS.

[BuckoA51]

Did the SCART cable you tried tap composite video for sync or did it have some kind of internal sync combiner?

[Felipe Rios]

Both scart cables are supposed to be RGB to Scart but I don’t know if composite pins are connected. I would have to take it apart.  I do have another Atari ST Scart cable from Cool Novelties. I will try that one.

[TheCorfiot]

Hi Felipe

ST and STe scart cables are notorious for sync issues where scart cables are concerned…

This is because they don’t natively have 5 or 12 Volts on the monitor connector which is usually used by other systems to derive the Fast blank switching voltage on scart Pin 16 which TV’s need to be informed to use RGB signalling instead of composite video.

Instead a “hack” which works most of the time was used using the Vsync signal and a 10uF capacitor to ground to provide a “rough” blanking voltage.

And Yes commercial cables used this.

The OSSC and Pro have no need for a fast blanking signal.

If you don’t mind trying an experiment…

Open your scart plug and look at pin 16… if it is connected by a wire then snip it.

Please double check your numbering….I cannot be held liable.

By all means upload a picture or 2 of your scart so we can advise further.

 

Most ST scart cables have

150R inline RGB resistors

330R inline CSYNC (pin20) resistor

• This reply was modified 8 months, 1 week ago by TheCorfiot.

[Felipe Rios]

Thanks for the assistance.  I tried both scart cables and neither works with OSSC Pro, but they work fine with the OSSC 1.6, so I will use the old one with with Atari ST and keep the PRO to use with my Apple IIGS and others.  I also tried a Atari ST to VGA cable and it didn’t work with the PRO.  The PRO just cannot sync with the STe.  I updated the firmware to the latest release.   Anyway, case closed 🙂

[marqs]

I’ve received similar report from another source so it seems the video ADC indeed has some issue with the sync coming from ST(e). I’ll debug this further if/when I have a chance to try one of them.

[marqs]

I just had a chance to try a 1040STF and one STE, and neither had any visible issues with Pro running latest fw. Both were PAL models connected via RGB SCART.

[BuckoA51]

The mystery deepens as I’ve just had a customer contact me by e-mail and his Atari ST (using SCART with composite video for sync) will not sync with OSSC Classic on 1.x firmware or OSSC Pro either.

Marqs can you open your SCART cable and determine how sync is generated? Composite video or some hack to combine H/V syncs together?

• This reply was modified 1 month, 1 week ago by BuckoA51.

[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).

[marqs]

The cables I tested were wired to csync, first one with 150ohm resistor in series and other one directly if I recall right. Is there a reason to use a series resistor with composite video since i don’t think a basic AV cable has such either? Does the 800mV include sync or just video? A nominal video signal should be 700mV between black and peak white, plus 300mV for sync. Only the latter is relevant for synchronization, and even with signal far from that you can try tuning threshold on OSSC side via Analog sync Vth option.

[BuckoA51]

ST actually only outputs hsync and vsync (or at least most models do), if you see TheCorfiot post above it seems some cables use a hacky way to get sync from hsync while others use composite video.

You’d have thought composite video was the better way to do it, but perhaps not. I was told composite video out has long a delay time on the sync causing the image to be shifted, but this could easily be corrected on either OSSC by adjusting backporch. I agree using a resistor on composite video seems strange but I’m no expert.

[marqs]

According to this units without RF modulator output csync, not cvideo. Anyway, both cables were wired to pin 2. That probably also answers my previous question why the resistor is there to make the cable compatible with both types of systems.

[BuckoA51]

Ah yes seems you’re right, pin 2 can be sync or composite video.. how lovely. Do you recall Markus if your machine had RF or not? I’m just trying to narrow down the problem here.

@retro-computer-shack any joy with adjusting Analog sync Vth?

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