PS1 Sync Problems

[ClaudioRSPeres]

Hi Brisma! First of all, congratulations on all the adjustments you made to the GBS C Pro! They look great!

I think I'm not the first to comment on the synchronization problems some consoles experience on the GBS Pro using a SCART cable. The main consoles the community mentions having this problem are: Mega Drive, PlayStation, Neo Geo... I suspected the power supply, so I bought a high-quality 5 amp power supply thinking that was the culprit, but the problem persisted... My report today is about the PlayStation 1 fat; on excessively bright screens, synchronization is lost. I've tested more than one cable and even made a high-quality cable, but the problem continues... We know that the GBS Pro itself has an internal Sync Stripper (LM1881) that shouldn't allow this kind of thing to happen, but is it being used or activated? Is there a way to force the use of this chip through the software?

Here's the link to my live stream at the moment the problem occurred:
https://youtu.be/LPzX9cszqjU?t=9126
https://youtu.be/LPzX9cszqjU?t=9334

[Killertamagotchi]

Is it definitely a cable for the PS1?

There can be problems with things like converters and scalers if the cable isn't actually for the PS1.

Because, like SNES SCART cables, PS1 SCART cables have different components depending on whether they're PAL or NTSC. For example, PS2 SCART cables might work with the PS1, but PS2 cables don't have those components built into the cable itself, which can then lead to problems.

[ClaudioRSPeres]

Yes, the cable is made to PS1 specifications, but it uses the Luma sync on the console... the composite quality is very poor.

[brisma]

Hi Claudio, thanks for the report!
The problem is your cable using luma sync - the sync signal gets mixed with brightness information, so on very bright screens the scaler gets confused and loses sync.

Try this:
Go to the Developer Menu → Page 6, and lower the SOG Level. This makes sync detection more selective and should help ignore those brightness spikes.

For a permanent fix, a SCART cable with true CSYNC would solve the issue entirely.

Let me know if it helps!

[ClaudioRSPeres]

Good evening Brisma!

I did the test but it didn't help, the problem persisted. I tested several values ​​from where you asked me to adjust them... in debug mode, when the synchronization breaks, I get this message:

. (debug) ign. lenght: 0x68

It's no use, my friend. The only thing that really solves the problem is the external switch that Cristian made, as shown in this video:

https://www.youtube.com/watch?v=hrDVrzMzsy8&t=4s
https://www.youtube.com/watch?v=87g9jVotA-w&t=303s

The problem with using composite sync (the original method) is that the image quality deteriorates considerably, while using luma sync results in a cleaner image!

The old GBS worked perfectly with the PS1 using that SCART-on-Luma cable; it's only the GBS Pro that has this problem.

[brisma]

Hi Claudio,
I took a closer look and made some interesting discoveries.
In GBSC Pro there is an LM1881 module, but it was set to “off” by default for RGB, so you had to activate it by playing around with the Compatibility Mode.

I did some refactoring of the code and renamed that option (Compatibility Mode) to Sync Stripper and enabled it by default for RGB signals.

I tried it with my PS1 and RGB SCART cable: I no longer see any “artifacts” on white screens, but I think the cable shielding is also a very important factor.

Can you run some new tests? Please note that you may need to perform a factory reset of the firmware, which will delete all saved options/presets.

[ClaudioRSPeres]

Hey Brisma!

If you look at my first comment, I said exactly that, that the GBS PRO has the LM1881 and that it probably wasn't active. Good thing you found that! If it works, it'll be a victory!

My SCART cable was made very carefully, with good grounding and shielding, because as I told you, I was suspicious of the cable and made one to be sure!

Wow, has the 2.3.0 update already been released!? You're awesome!

Sure, I'll do the tests as soon as possible. It's no problem if you clear the configs. Anything I can do to help you with this project, you can count on me! As soon as I test it, I'll post the results here.

[brisma]

Yes, sorry, I forgot to mention in my comment that I had just released an update with this change.

Let me know if you see any improvements. Please note that sometimes, after changing this option, you need to turn the console off and on again to force the new sync.

P.S: My nickname is Brisma, not Brisa :P

[ClaudioRSPeres]

Hi Brisma, sorry for the "Brisa" part, lol.

I updated to version 2.3.0 as you recommended, checking the option that clears all profiles to avoid errors.

I connected via remote to the RGB port, set the resolution to 1080p, in picture settings I set ADC gain to 100, sharpness ON, in System Settings ADC calibration ON, Firm time lock ON, HDMI limited range OFF, and finally I activated Sync stripper ON.

And lastly I turned the console off and on again to adjust the sync.

But the problem persists in Street Fighter Alpha WD... I think maybe it's a hardware issue with the GBSC Pro that needs a resistor or something like that :/

[VeCAD]

Good evening Brisa!

I did the test but it didn't help, the problem persisted. I tested several values ​​from where you asked me to adjust them... in debug mode, when the synchronization breaks, I get this message:

. (debug) ign. lenght: 0x68

It's no use, my friend. The only thing that really solves the problem is the external switch that Cristian made, as shown in this video:

https://www.youtube.com/watch?v=hrDVrzMzsy8&t=4s
https://www.youtube.com/watch?v=87g9jVotA-w&t=303s

The problem with using composite sync (the original method) is that the image quality deteriorates considerably, while using luma sync results in a cleaner image!

The old GBS worked perfectly with the PS1 using that SCART-on-Luma cable; it's only the GBS Pro that has this problem.

Interesting, I get a similar log when switching PS2 to progressive mode. SCART RGB with sync on CVBS cable.

. (debug) ign. lenght: 0x68

Oddly though Retroscaler's version gbsc pro comes already with a 1881 stripper. I haven't tested the 2.3.0 release yet though which has changes to handle the 1881 switching.

[ClaudioRSPeres]

Hello Brisma

I'm sharing a friend's report (in video) with a Neo Geo CD that had the same synchronization problem in the original GBS C PRO mode with the option you mentioned enabled... and then he tested with a physical switch (MOD) where he installed a separate sync stripper. With the switch off, the GBS C PRO is in its original mode, and with the switch on, it uses the separate sync stripper, working without the problem... that's what the LM1881 chip in the GBS C Pro itself should do, filter the signal to prevent synchronization loss, but it's not working... are you sure you're actually enabling the LM1881 chip?

https://drive.google.com/file/d/116bgx1n5fi1IgqhDkKASiITKW6jDAlT9/view?usp=sharing

[brisma]

Hi Claudio,
Yes, at the firmware level, the LM1881 filter is actually used: for example, with my PS1 PAL connected via SCART (luma on sync), only by activating the filter can I obtain a stable and filtered signal, while with the filter deactivated, the signal is unstable and has many glitches.

Keep in mind that the onboard circuit may not be as efficient as an external filter, which would explain why an external modification results in a better signal.

In addition, we have discovered with some users that a batch of faulty devices has been distributed, presenting various problems (such as an unstable/crazy OSD after a few minutes of use), so I cannot rule out that the behavior may vary from device to device, old and new.

Since I am unable to replicate the problem on my device, I am having a lot of difficulty testing it/finding a solution :(

[warheat1990]

I have the exact same issue with Saturn. Bright scene would lose sync. I'm using RGBS with CSYNC.

saturn.mp4

https://streamable.com/vhmbb6

I tried putting 680 ohm and 100 ohm resistor on the Sync and GND but it doesn't help, 100 ohm actually makes it worse. I'm still using original firmware, does latest firmware from this project fixes this issue? @brisma @ClaudioRSPeres @VeCAD

Note: the cable I used is VGA from this project

https://github.com/jeffqchen/10DIN2VGA

I also have cheap SCART cable from Aliexpress and it doesn't have this issue.

[warheat1990]

@brisma Tried your firmware (which is awesome compared to stock) but still getting issue with Sync Stripper ON. I have a hard time to see the developer console log as it hangs when I turn on the console (only accessible when console is off).

What is the recommended SOG Level?

@ClaudioRSPeres Got any guide/schematic to install the LM1811 switch mod? I saw the video you posted but I don't understand portugese, are these mod open source/sold somewhere? Where do they get it from?

[ClaudioRSPeres]

@warheat1990 This external sync stripper modification was done by my friend Cristiam (who made the video). In his videos, he more or less teaches the method, which is a switch that turns the eternal stripper on and off. When the switch is off, the GBS PRO is in its original state; when it's on, it provides a clean sync signal to the SCART and RGBS outputs, all because the AV signal is interconnected with the sync. I asked him to make a tutorial, but the guy is stubborn, haha.

If it worked well with the normal Saturn cable, it might be something in the cable you built. From what I discussed with Brisma, C-sync signals that don't come from the composite, like Luma and pure C-sync, cause problems with the GBS Pro... but that's what the stripper is for, to filter the Luma and pure C-sync so that the signal is within the standards. That's what I'm still wondering if it's happening or not...

[warheat1990]

@ClaudioRSPeres Yeah that's what is happening, my cable is pure CSync as I'm using Extron Crosspoint.

If your friend wants to sell/share the schematic, that'd be great. Let me know

@brisma I wonder if this is something that can be fixed via software since the GBSC already has LM1811 inside.