Help :( CGA->VGA adapter - screen jumping problems on a bright video signal

Tech Talk
#1

http://cgi.ebay.co.uk/Video-Converter-PCB---CGA%2FEGA%2FYUV-to-1-x-VGA_W0QQitemZ170452285320QQcmdZViewItem?rvr_id=&rvr_id=&cguid=bed98ef31280a0e2035676a6fe6ec0a4

I bought myself one of these out of curiosity for what it claims to do, which is essentially a DIY version of the XRGB upscaler for 1/4 of the price that converts a non VGA compatible RGB signal (CGA/EGA) to a VGA signal.

I’ve wired up a Euro RGB scart block to one of these, via the 8-pin VGA input header - wiring the RGB lines, sync/composite line and ground. So far - picture quality is insanely impressive than the Hori Upscan Converter 2, being a native RGB picture - and I’m quite certain from the corner of my eye, there’s 1 frame less of input lag on the CGA to VGA converter.

There’s only one HUGE problem stopping me from selling off my Hori adapter. When the game has to output lots of bright colours, especially white - the video signal loses sync, and the whole screen becomes a mess. But when it outputs a picture with not many bright colours - the video signal is completely stable. (I will post up a YT video demonstrating the problem).

I was wondering if anyone (more specfically supergun builders) has bought anything similar to this, and if so - if they have found a way to get rid of this annoying screen jumping problem.

Update: Problem can be seen here - [media=youtube]5DcvsYf0H8s&feature=player_embedded[/media]

Left screen is using a Hori Upscan Converter (S-Video), and the right screen is using the CGA/EGA adapter. (Video quality cannot describe how much better the CGA/EGA adapter is).

http://img716.imageshack.us/img716/6730/dsc0041wj.jpg

#2

What’s the wiring look like? My guess is when all the lines go high during a high color situation, something happens and sync is lost(duh), so are they all wired to their own ground? Or are they all tied together with sync?

Pics would be helpful :slight_smile:

Disregard, I suck cocks.

Seems that SCART sends Composite Video, not just Composite Sync, over the SCART line. Are you cleaning out the Sync from Composite?

Use one of these: http://www.national.com/ds/LM/LM1881.pdf if you can.

#3

Essentially all I’ve done is taken the 8 pin header that came with the package, and soldered the following:

Red wire -> Scart Pin 15 (Red Input)
Green wire -> Scart Pin 11 (Green Input)
Blue wire -> Scart Pin 7 (Blue Input)
Grey wire -> Scart Pin 20 (Composite Sync Input)
Black wire -> Scart Pin 21 (Common ground) - daisy chained onto Scart pins 13, 9 and 5 (colour ground pins)

Yellow wire -> Unused (assuming is used for RGBHV connections)

I have also tried stripping an old PS2 RGB scart block, and wired them directly into the board - only omitting the same results.

It’s funny you mention the LM1881, as I’ve actually got one currently soldered in a failed project to make a PS2 Progressive scan adapter from several years ago. I just never figured out how to get it working. However, according to the instructions - even if I can convert RGBS to RGBHV - it states that the input signal for RGBHV is 31K as opposed to RGBS’ native 15K.

#4

Made some progress. I didn’t actually realise that the video signals are extremely prone to intereference. I wrapped about 4/5 of the 8-pin harness with kitchen foil, with a ground wire attached to the foil with electrical tape, and the video appears to be more stable at brighter scenes.

It might be the case of buying some heavily shielded cable, that and probably finding a way to ‘weaken’ the RGB signals maybe?

#5

Have you tried turning down the brightness on the RGB pots? They are right next to the input header and iirc you have to turn them clockwise to turn down the brightness of each color.

#6

Turning down the RGB levels makes no difference, even at it’s lowest settings. It will still lose sync constantly during the 3s intro.

Also, the shielding theory was a myth. Even tried wrapping the entire harness in kitchen foil with a grounded wire attached to it. The problem came back.

#7

Just for shits and giggles try using the RGBS header instead of the RGBHV header.

You could also try the component input, and see if it has the same problem.

It has been reported to me that those boards lose sync sometimes. I have had a couple of them, and never seen the problem myself.

#8

The RGBS and RGBHV headers share the same signal lines.

My current Hori Upscan Converter is Component Input to VGA. The colour quality and clarity on RGBS is quite significantly better, specifically when it comes to low contrast areas - it’s just a shame the screen starts jumping before I could admire it :confused:

#9

It would only take a few minutes to switch the lines over to the rgbs header. I would want to exhaust all options if I were troubleshooting it.

I would be checking the component input, just to see if the board itself is defective.

Then I would try it with a true RGBS signal, like from an arcade board, and/or try it with a lm1881 circuit.

#10

my brother and I have these boards. IMO, the board is just really fickle when it comes sync. If I have my CPS1 SF2HF board hooked up to it (which in turn is hooked up to a LCD monitor), it’ll lose sync every 10 seconds or so (I believe that the HF as well as older arcade games output at a V and H frequency that this board has trouble maintaining). However outputting the arcade board via s-video with JROK to the monitor provides a stable picture.

I’ve gotten slightly better stability when I used component cables from the jrok to the VGA scaler board (opposed to wiring the supergun to the board directly through the plugs).

My brother also notes an improvement in not using the plugs and just soldering the wires directly onto the pins.

All that said, the boards have provided a stable picture when it came to CPS2 and naomi games.

#11

I’ve already tried the RGBS header, both headers use the same lines anyway. So there isn’t any difference.

Found out some more stuff. It appears that whilst I have my soldering iron on, which is right next to the adapter, it significantly desyncs the picture. Turning it off, and it becomes stable again - although it still can’t handle bright images without going crazy.

I think it all bottles down to electrical interference or some sort, which I don’t really understand.

#12

How big is the power supply you are using? I remember reading on another forum that a guy was having issues with his, and he found that the power supply he was using was too small. IIRC it requires +5V @ 2 amps.

#13

depending on where you shop for it, you can get the 2 pin lead which would go directly to an AC wall jack. Or you can wire it directly to the power supply (or get an AC/DC converter from radio shack).

#14

I’m using the power from a USB port on the PS2, in which I’d imagine is 5v.

#15

D’oh. It could well be the power output. A USB port only outputs 5v 500mA. If 1000mA = 1 Amp. Then I’m 1.5A short :confused:

#16

Bought a 5v 2.5A DC adapter. No difference :confused:

Then out of curiousity, from my multi AV cable - plugged the composite plug into one of the component jacks - the sync stablisation improved dramatically although still not perfect (when the screen is 90% white, particularly the first image of the 3s intro, and Akuma’s raging demon animation). So it clearly suggests that the sync signal is the culprit, meaning that I need to find a way to get a 100% clean sync signal and still withstand interference.

#17

Working Perfectly!!!

http://img413.imageshack.us/img413/2601/dsc0045sg.jpg

By vkcfong at 2010-06-09

Reworked on the old LM1881 circuit, eventually finding out that I didn’t ground one of it’s pins. Used the 5v header from the converter board to power up the chip, fed the composite signal, and outputted a clean sync signal without being affected by bright visuals in RGBS mode.

Makes me wonder tho - the converter board really should have had an LM1881 built into the circuitry surely?

Hori Upscan Converter
http://img716.imageshack.us/img716/1158/dsc0044yf.th.jpg

CGA converter
http://img532.imageshack.us/img532/2262/dsc0043b.th.jpg

#18

whats the LM1881 circuit needed for anyways?..

#19

No, like I said, SCART looks like it outputs composite video, which is an amalgamation of red, green, blue and sync onto a single line. SCART TVs are aware of this, and clean up the sync internally. Where this thing would be used, it’s assuming a clean sync signal; either from a JAMMA board or some other RGB+S source(Like say, Japanese style RGB).

Putting the LM1881 inline with the composite video gives you a raw sync signal. I theorize that when the colors hit high levels, it futzed with the sync the CGA converter was looking for.

Can I declare victory on this one? :bgrin:

It takes a composite video signal, and strips away the color and luminance data and returns only the sync data. Solves the problem we see above.

#20

It depends on how the scart cable is wired, and whether the TV accepts RGB SCART. A cheap scart plug (i.e. a relatively dirt cheap one) would only have the composite and audio lines wired.

A fully wired scart plug running in a TV that accepts RGB scart will give you an RGB signal. A cheap scart plug may only give you composite video.

A fully wired scart plug running in a TV that doesn’t accept RGB scart (or is in ‘composite video’ mode) will output a composite signal.

Technically, Euro Scart and JAP Scart are the same, but the pinout standard is different.

Sorry, victory denied. But the difference between composite video and RGB scart are extremely distinct, since the reds from the RGB signal burns my eyes lol