Philips TV 15khz NTSC TV CRT Display Sync Issues on Some Cores but Not Others

[mukiex]

TV Model: Philips 20pt6441/37

I came across this problem today. Namely, that Philips TVs don't seem to get a good sync signal from some of the console cores. The most notables are SNES and Genesis. The Neo-Geo and Turbo Grafx cores (along with SMS I believe) don't have this issue.

Basically, it looks like Philips TVs are using a shade of black to differentiate the blanking signal, and the SNES/Genesis cores send this same level of black out as their normal bottom-level blacks. While this probably results in a better image overall, it makes it impossible for those cores to sync until a game fills the screen with a different color. Unfortunately, a lot of games on SNES and Genesis don't do this, and the core doesn't do this as well.

• Turning the Genesis "border" on fixes it for games that use anything but pure black as their border color as soon as that border appears (usually at title screens).

• Any Konami game fixes it when the background gets swapped for the white "flash" at the end of the Konami logo animation.

• Even "World of Illusion" fixed it with its slightly-grayer-than-black title screen border.

Is there any way this could be fixed? Like maybe a brief gray or white full-screen image right before a game loads?

[mukiex]

Another quick hardware stat: I'm using IO Board 6.0.
MiSTer's software was updated yesterday with the update_all script.

I was able to further test this "black level" theory with the Gamma curve. I created a "TestSNES.txt" gamma profile. I basically tried raising the black level until loading a new rom would immediate come up synced properly. (the SNES core resets sync every time you load a new ROM, so sync fails every time)

Basically I'd just set all the entries from 0 to X to whatever value X had, going higher until I got a working signal. So everything from 0 to 20 would equal 20. If that failed, everything from 0 to 30 would equal 30, and so on.

So it's 48. The gamma curve on the SNES core putting absolute black at 48 would immediately load with proper sync. Obviously this grayed the screen out a bit (my personal hypothesis had been at 15/16, so that was completely wrong). Anything lower than 48 will cause a sync fail.

So I guess that comes back to the original query; can the core "initialize" with at least one gray frame at a value of 48 or higher? This would probably fix sync issues for a lot of people.

edit: Looks like on the Genesis core, this trick fixes hsync, but not vsync, and it ends up with a weird kind of rolling shutter as the vblank line slowly moves up the screen. Interestingly enough, toggling SOG off/on seems to fix this. Though if you do it w/ the Gamma turned back off, horizontal sync breaks again.

[ioev]

There was a thread a while ago about adding some silent noise to the video/audio signals to help with similar problems over hdmi: viewtopic.php?f=29&t=661

I wonder if something like this could help here as well? Something like the gameboy core's "Stabilize Video" feature, but would insert low level black frames.

[mukiex]

I would love to figure out what the Neo Geo video chip is doing. It didn't even fall out of sync when I switched to PAL on this TV!

[Shogun]

Has anyone come up with a solution to this? I hauled my Philips CRT out of the basement to pair with my Wega using a VGA splitter - one for horizontal games another for tate. However the Philips is exhibiting the sync issue. It will sync as soon as something bright on the screen appears (ie Konami logo, or Garegga's Saturn flashing intro). I thought maybe if you could have a solid white background color in the core instead of the snow it would force sync but I don't think you can do backgrounds in analog output.

[Shogun]

So I've been doing some reading and one thing that keeps coming up is the sync on the I/O board not being great? In a youtube video posted about this problem the following comment was made:

The issue is probably directly related to the resistor that sets the depth of the sync. The analog IO board's sync is way out of spec and it should be a lot deeper. E.g. 100-150mV with the Analog IO board, while spec should be 240-300. I'd probably go down the RGB to Component converter board with a proper 430 ohm resistor. (330 for direct video)

In another thread posted here MikeS1 mentions:

As for the sync, like others have mentioned, the sync out the analog Io board is not great. I recommend a 430 ohm resistor if your using the analog Io board and if using direct video 330 ohms. These are actually the values I'm using for my new board.

The schematic on my board (5.6 XL) shows the following for the R1 resistor:

TCMQ12M.png (125.08 KiB) Viewed 1976 times

So does that mean a possible solution is to just swap out the 510 ohm resistor for a 430 ohm one to clean up the sync out? Has anyone done this? It'd be a pretty simple fix if that was that case but I'd like to verify first.

[Shogun]

I emailed mister add-ons and asked about the R1 resistor and he confirmed the output isn't great on the IO board and to go ahead and replace R1 with a 430 ohm resistor. So I ordered a few different sized SMD resistors from Digikey and the 0805 size looked to be a match. I tested some of the cores on the Philips to see which cores had sync issues before I did the swap and found the following:

Code: Select all

NES - Works
SNES -No
SMS - Works
Genesis - No
TG16 - No
NeoGeo - No
Saturn - No
PSX - No
Arcade cores?
CPS2 - Yes
Cave 68000 - Yes
IREM M92 - Yes
Namco PacMan - No
System 16 - Yes

After swapping out the 510 ohm resistor to the 430 ohm resistor I booted up the Mister and did the same tests and unfortunately nothing changed. Swapping out the resistor had no impact. It did however seem to cause a very slight yellow hue on the Phillips. So greens look neon green for example. Its really subtle and probably just some adjusting needs to be made on the tv itself. If my soldering could cause the yellow issue or the different resistor please let me know. This was my first time soldering SMD components. (Edit - I swapped the 510 resistor back and it appears the yellow was always there. It could be the mister but it could also be the component input as S-video does not exhibit this yellow hue on whites.)

For the most part this is just an annoyance and I can get sync after some bright screen or flash. The only games which remain unsynced despite whatever is on the screen are some arcade cores such as the PacMan. The Cave core used to do this as well but there was a recent fixed which cleared things up.

[MikeS1]

Thought it might be related to the Hsync / Vsync Lengths but ran some of these cores through a scope and here are some results :
MENU - 4.6us (Vsync 3 frames - 190ms)
Genesis - 4.2us (Vsync 3 frames - 190ms)
NES - 4.7us (Vsync 3 frames - 190ms)
SNES 4.3us
TG16 - 4.5us
PSX 4.7us
CPS2 (Loading) - 4.7us
CPS2 - 4.7us (Vsync 4 frames - 255ms)
Midway PACMAN - 5.4us

Cave previously was 2.Xus and I moved it to 4.0us but it also had a VSYNC of 2 frames which I bumped up to 3 frames.

I would think most of these should work if it was related to the HSYNC timing..

Have you tried just using a HDMI to VGA dongle for component out? (Adding a resistor and diode). The only problem i've seen from analog out was on my JVC DTV and some jitter with sync but using an HDMI to dongle cleared that up

I'm actually curious to know an Active S-Video / Composite adapter works on these displays through analog out..

[Shogun]

I think you replied to the comment I made on youtube as well? You asked if the real console works. I don't have a 1 to 1 test I can do since I'm using VGA out on the IO board to the component in on the tv, and of the consoles I have, they are mostly S-video. I hooked up my Saturn via S-video (4 pin) and it worked fine. This Philips CRT I've had since I bought it new back in 2003 so I've used it with many consoles over the years and never had an issue but the only consoles I would have used the component port for would have been PS2, Wii, or Gamecube.

I'm sure using Direct video would work I just really like the ease of use of the analog out. I don't have to mess with modelines or do mods to get it to work.

I haven't looked into the S-video aspect yet as I only have a VGA to s-video cable and that doesn't work as far as I know.

From your measurements the menu always works and if we compare that to a genesis its very close so what is throwing things off? I have a scope too that I'm still learning to use but if I can help with anything let me know!

Other things I have tried that didn't resolve the issue:
-Using a component video switch box (Psyclone) - Same video signal probably gets sent out
-Using my Extron Emotia - Couldn't get a stable image even in working cores (probably user error I haven't used it in years)

My Philips is a model 20pt643R01. I've attached the service manual if its of any use.