Loosing Sync with Ossc and Pc Engine

[easterislandnick]

Hi, I have a PC engine that I am trying to use with an OSSC, I get a great image in 2x mode for around 5 minutes, then it starts to loose sync, it flashes out and comes back until it eventually only displays a black screen. I am using a db GrafxBooster TTP to get scart out of the PC engine.

db GrafxBooster TTP

Some games seem more stable, but Outrun always losses sync before a race.

The OSSC reads AV1_RGBS 262-p 15.72khz 60.01hz to 60.28hz seemingly dependent on the game?

I have tested with a cheap old HDMI converter and get a stable but horrible image. My SNES and NES have no issues with the OSSC.

Any ideas what I can tweak to get a stable image? Let me know if there is any more info I can give.

[BuckoA51]

Have you got the graphics booster set to 75 ohm output? Hopefully it was set to this by default.

Set pre and post PLL coast on OSSC to 4 as a first step (under Sync opt.)

[easterislandnick]

I don’t get an image at all if I set it to 75, if I set it to TTL I do but even with setting ppl coast to 4 it still looses sync. I’m not sure what this jumper is for?

I am using this cable…

https://www.ebay.co.uk/itm/154485800631?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=AN0xTLJRTJG&sssrc=2349624&ssuid=kZrc4a8sSSi&var=&widget_ver=artemis&media=COPY

It wasn’t expensive but I get a great picture with my OSSC and megadrive 2.

I have tried with another even cheaper cable but get the same issue.

[BuckoA51]

Something is not right there then, can you check with the manufacturer because using TTL pass through will damage the OSSC. Unless the attenuation is supposed to be done in the cable itself

[easterislandnick]

Thanks for letting me know about TTL, I shall not use it any further. I don’t think dB electronics are still going so I can’t ask about it. I’m going to get a cable from retro gaming cables once they have one back in stock. They advertise their megadrive 2 cable as working with this booster so I’ll see if that makes a difference.

[BuckoA51]

it may be the correct setting but you need to check the documentation, if the attenuation is done inside the cable (which I believe it should be for a standard Megadrive 2 cable).

[easterislandnick]

Hi. I’ve checked and the booster needs to be using TTL with a megadrive 2 cable. I have checked and my cable is wired to lower the TTL signal.

Any idea what setting I should try next?

[BuckoA51]

Try analogue Sync Vth to around 101mV and the Vsync Threshold to somewhere around 11.3 to 11.9.

[easterislandnick]

I’ve had a good go with those new settings and still got a lot of synch. Have you got any other tips?

[marqs]

You can also try setting “Analog STC LPF” to “0.5MHz (SDTV)”, but typically that is only needed with poor quality sources so it might not help here. Just to rule out sync circuitry of db GrafxBooster TTP, you can also try hooking composite to OSSC’s Y-input (green RCA), select AV2_YPbPr source (should show B/W picture) and see if you get any sync losses there.

[easterislandnick]

Hi. No luck with setting it to .5mhz (sdtv) and when I tried the composite and I got a solid image in b+w. My test game is outrun, as soon as I launch into a race on the OSSC it loses sync but I could play the race over composite and on my cheap scaler.

[BuckoA51]

if it’s always losing sync at the same point then that could be the game changing screen resolutions, but that’s not the impression I got from your original post.

[easterislandnick]

Sorry should have been clearer, outrun always loses sync at the start of a race but other games like soldier blade loose synch during normal play. It takes around 5 minutes so is more of a pain to test. A resolution change should still be supported though shouldn’t it? Just with a black screen as it changes?

I’ve ordered some new caps for it to make sure it’s not old caps putting out a poor signal or something.

[marqs]

If the random dropouts only start to happen after 5mins, then either OSSC or PCE might have a HW issue. If you have a desktop fan nearby, perhaps you can try if blowing air into OSSC makes any difference (if you have v1.7 case, its top part could be removed too). Also, does OSSC light up red LED when it loses sync?

As for Outrun, perhaps someone can confirm if it changes between interlace & non-interlace at that moment? Otherwise I don’t see a reason why there should be an interruption / change in the sync signal.

[easterislandnick]

Hi. Thanks for your help. In have replaced the capacitors in the pc engine and still get the same issue. I don’t think the OSSC is faulty as it handles mysnes, nes and megadrive 2 okay. The OSSC does light up red when it loses sync. It’s very frustrating seeing the cheap scaler works okay but there must be something up with the pc engine.

I have also tried another type of av booster on it as well and get the same result with the OSSC, it loses sync after 5 minutes or so.

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