Trouble with PCBs on TV

[NFG]

I have a problem playing arcade games on my TV.  It's got RGB SCART, and the picture displays just fine for up to 30 seconds at a time, but then it flashes white and/or loses sync for up to half a second.

It does this for NEO MVS, and Capcom CPS2, and CPS1.

It does this in RGB (direct),
RGB through an X-RGB2,
encoded S-video
encoded composite video

I can't figure it out.  There's no parts the same: different power supplies, one running 120V the other 220V.  Different video cables (RGB, composite, Svideo).  Different RGB connection methods (via the XRGB or not).  Different PCB hardware.

If it was a problem with the RGB, using the encoded signal should have fixed it.
If it was a problem wtih the PCB, changing games should have fixed it.
If it was interference from the 120V stepdown I use (which is a massive thing powerful enough to run a whole house) using the 220V PSU should have fixed it.


I'm out of ideas.  It looks and plays beautifully, but then it skips again.  It happens often enough that it makes games decidedly unfun to play.

No consoles have any trouble, just the PCBs.  =(

[Hojo_Norem]

Hmm. Odd that.   What make of TV is it?  I suppose the first thing you could try is putting a 75 Ohm resistor in series with the composite pin on the scart plug going into your TV.  Secondly your TV may just not like a 60Hz video signal, I have seen some old sets have no problem with 60Hz and some newer sets go funny in different ways.

[blackevilweredragon]

Wait, aren't those games the ones with odd scanrates, that weren't 15KHz?

[Hojo_Norem]

Wait, aren't those games the ones with odd scanrates, that weren't 15KHz?

The NEO GEO MVS should be 15KHz, I use one on my 21" Panasonic (A TX-21MD3 if your wondering) with no problems.  However, I am unsure about the CPS boards.

EDIT: Ah, Lawrence.  Are you using  pre-made cables for your consoles?  That might explain why they they work fine.  If you have made a cable for your PCBs yourself (I suppose you would have to) have you got pin 8 and 16 of your scart connector wired to +5v via a 100 Ohm resistor in series?  I have noticed that while some sets are OK with just +5v, some need the resistor and some sets need both pin 16 and 8 to properly use RGB and will just flip out if they don't get a signal on pin 8.

[NFG]

I don't get any display at all without putting voltage on the proper pins, but you're missing the point: it does the same thing with Svideo and composite, which don't use the SCART connector at all.

The TV is a dual standard (50/60Hz) unit, and does not support progressive, only 15kHz standard-def signals.

[blackevilweredragon]

try putting resistance on the connection when using composite video, as a test..

On my Commodore 64-clone monitor, sometimes the picture will just when something flashes, or if the picture gets too bright, it looses vertical hold..  I found on the back of the monitor, a POT, that ADDs resistance to the signa, and when adding resistance, it really helps..

This might work for you...  If it works on Composite video, then figure out how to do it on RGB (cause im not too sure which pins you add the resistance too on RGB)

EDIT:  Oh, and im sure it supports non-interlaced modes, just the low-res stuff (240p), cause im sure that's what those arcade boards run in    

[NFG]

The screen loses sync or flashes solid white, and sometimes both.  It's got nothing to do with what's being displayed, sometimes it will do it for a black screen.

It's got nothing to do with the resolution, 'cause the PCBs run on similar resolutions as consoles.  The Neo home system works fine on the TV, but the arcade doesn't - resolutions and refresh rates are officially ruled out, since the hardware is the same for both.

This would normally have led me to blame the power supply or the stepdown, but since I've swapped PSUs and bypassed the stepdown with the same end result, I kind of have to rule those out as well.

[Midori]

What kind of power supplies are you using? An arcade PSU or an Computer PSU och something else? Does the sound in the games in any way respond to the problem with the picture? Or is it only the picture that isn't working correctly?

[viletim!]

That really is bizarre! Some things I can think of...

Check the grounds. Not just by looking at the wires but use a multimeter to measure the resistance between the power supply and TV (via exposed A/V jack or something). You could also measure the voltage between PSU/TV while they are running...should be 0v but you never know...

Maybe try to isolate the sync signal...try to narrow down the problem. Disconnect the R/G/B video lines. Just feed the sync (encode it into composite 'video' if you like) and see if the problem persists.

Does the problem coincide with any specific change in the video or sound?

[NFG]

viletim: yeah, grounds were something I'd thought of also, especially since the TV uses a 2-prong power connector instead of a 3...  but it's really kind of extra-strange, the XRGB-2 does it as well, regardless of what's attached, so the problem is the same with or without it, and with or without a PCB attached.  Using the CPS Changer with its chroma encoder I thought the problem would go away, but it's still there as well, no matter what PCB I use (and again, different power supply).

Why would the dreamcast/SNES/MegaDrive/gamecube/saturn/PS/whatever work just fine but two PCBs and two power supplies and the XRGB don't work?  It's bloody bizarre.

I should point out that all these systems, consoles + PCBs, work just fine on a little RGB monitor sitting next to the TV.  It's just too small.  =/

Edited to add: the sound is never affected.  The only time I run the audio through the TV is when the CPS Changer is attached, otherwise it runs through the stereo, but in both cases the sound is not affected.

[Midori]

If I am not remebering terribly wrong the voltage on RGB lines for the consoles and arcade games differ, while the consoles have 0,7 V while the arcade boards have 1-3 V. Maybe your TV doesn't like that fact? Or am I wrong about my statement about the voltage levels?

[NFG]

You're right, voltage levels on PCBs are higher, but I think considering this as part of the equation is a bad idea for two reasons:

1. I've run it through the XRGB2, which converts the signals to a monitor and TV-friendly level, and
2. I've used chroma encoders to change the RGB to composite and S-video.

Also, I've checked the GND voltages between units:
no more than .06V between any two devices, and between the XRGB and TV it's .01V, between the PCB and stereo it's about .02V.

Not really sure if that's within tolerance or not, personally I'm surprised to see ANY voltages there.

[NFG]

Just an update:

the Neogeo home system is now the worst offender.  It rolls more than it's stable, and is completely unplayable.

It works with:
GameCube, Saturn, PS2, PCEngine (with RGB Amp) and MegaDrive.

It fails to work with:
Neo MVS + Home system, XRGB2, CP1 and CP2 arcade boards (both RGB and composite/Svideo)

This totally baffles me.  arcade trouble I could see, but Neo trouble?

There are no common denominators in the non-working devices: different power and video cables, different connection methods (RGB/composite/Svideo).

What does that leave?  Sync intolerance?

[blackevilweredragon]

have you tried using a current limiting resistor?  i don't know if you tried bringing the voltages down to the proper voltage levels...

[NFG]

That might make a difference if I was only concerned with RGB, but it shouldn't affect both composite AND svideo as well.

[blackevilweredragon]

yes it can..  because composite and svideo also have a voltage, if im not mistaken..

and even though it's going through a circuit that's filtering it, those circuits are supposed to keep the levels the same as they are received, so it would be outputting a high voltage composite and svideo too...

i still say try it..  my commodore monitor haves high input composite and svideo, it does the same things..

[viletim!]

Lawrence,
Does the TV loose horizontal and vertical sync or just vertical?

[NFG]

viletim: It only loses vertical sync, never horizontal.

[Hojo_Norem]

Sorry for sounding like a broken recording of a parrot, but have you tried putting a 75 Ohm resistor in series with the composite sync on your boards?  I hacked open my Gamecube's composite connector and it has a resistor and a cap in it.  I bypassed the resistor and the picture would roll under certain circumstances.  This would also effect the TV when using RGB and would only be 100% stable with the resistor in place.

[NFG]

butter: I really believe that by encoding the RGB into video or s-video I've created an all-new sync signal that is no longer affected by the original's lack of termination.  Wouldn't you agree, or do you know something I don't?

[blackevilweredragon]

just by converting something to another signal doesn't mean the signal will get fixed automatically..

what goes in broke, comes out broke..  what goes in good, comes out good..

[Hojo_Norem]

butter: I really believe that by encoding the RGB into video or s-video I've created an all-new sync signal that is no longer affected by the original's lack of termination.  Wouldn't you agree, or do you know something I don't?

Hmm,  isn't the sync the only thing in a video signal that DOSEN'T change when it gets encoded from RGB to S-VID and then Composite?  Isn't it the fact that it is possible to feed composite sync into the compisite video pin on a scart along with  RGB and get a perfectly viewable picture (well, at least I can, when I use resistors on all the signals)?

All I know is that when I have been wiring up my own connections I have used 75 Ohm resistors on all the video signals and I have had no problems at all.

Will it hurt to at least try?

[NFG]

I'm using Capcom's CPS Changer for the conversion.  It's a unit designed to create TV-friendly signals from PCBs, built by a company who should know what they're doing...

Will it hurt to at least try?

Hell yeah it will.  

[blackevilweredragon]

well without trying, there's nothing else we can really do...  

from my own experience, the symptoms you are experiencing is a too high of a sync...

[viletim!]

I'd say the TV simply doesn't tolerate the slightly out-of-spec timing of the sync signal (the vartical part specificaly) that's generated by your gear. Check the width the vertical pulse with an oscilloscope if you have access to one. I can't think of any other rational explanation.

Can't you just replace the TV? You managed to replace everything else.

[Computolio]

   Reminds me of the crazy problem I was having with a combo monitor. I never did narrow it down, partially out of laziness and partially because I wound up getting a different monitor.

[Segasonicfan]

This is a pretty curious problem, the only thing I can guess is that it's a problem with the sync line.  Have tried using an LM1881 or similar circuit?  Also, you may want to consult JROK, he is selling new a new "sync cleaner" circuit board that is very nice (and cheap).

-Segasonicfan