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Author Topic: Black and white picture with VGA to SCART RGB adapter  (Read 502 times)

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asdf015

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Black and white picture with VGA to SCART RGB adapter
« on: July 04, 2024, 10:07:44 am »
Hello,

I have bought a VGA to SCART adapter (Vga2Scart sync converter from retro-upgrades) to use with CRT emudriver, but I'm only getting a black and white picture.

Here's what I have tried so far:

- Three different older and newer Radeon graphics cards connected via DVI-I, VGA and HDMI
- Tested CRT emudriver on Windows XP, 7 and 10
- Opened the SCART cable to make sure it's fully wired
- SCART pin 16 (RGB select) is at 1.5V. When I set it to 0V (composite video mode), I get a black screen.
- SCART RGB output pins on the Vga2Scart adapter seem to be working properly (each 0.53V on a fully green/red/blue screen)
- Changed the color options in the ATI control panel, it's getting lighter and darker but still no colors.

My TV is an LG Flatron RE-21FB50RX from 2003.

Before this, I had been using a Medion graphics card that has direct SCART RGB output, so I believe that my TV supports RGB over SCART. I have also tried removing the individual RGB pins one by one, this makes the respective "color" on the screen go black, confirming that the TV is operating in RGB mode.

I have asked the seller of the Vga2Scart adapter, they have not heard of this problem but suggested that I try 50hz instead of 60hz, that didn't help sadly.

Does anyone know what could be the problem?
« Last Edit: July 06, 2024, 12:48:06 pm by asdf015 »

asdf015

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Re: Black and white picture with VGA to SCART RGB adapter
« Reply #1 on: July 04, 2024, 12:40:52 pm »
I did another test: I created some RGB test images that I displayed full screen, and then I measured the RGB pin voltages at the SCART socket.

The first test image consists of all three RGB colors at once in columns, and then I created three more test images that consist of just one individual color.

The voltages that came from the Medion PC were 0.2v on each RGB pin for the three-column image, and 0.55v on each pin for the individual color test images. The voltages from the CRT emudriver PC were almost the same (0.18v for the three-column image, 0.53v for the individual color images).

I just don't understand why the TV does not show the colors if it's receiving the same input signal from both PCs.
« Last Edit: July 06, 2024, 12:44:30 pm by asdf015 »

lilshawn

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asdf015

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Re: Black and white picture with VGA to SCART RGB adapter
« Reply #3 on: July 05, 2024, 05:00:27 am »
https://retrogamingcables.co.uk/Black-and-white-image-on-tv-when-using-an-RGB-SCART-cable

Thanks. I went through the reasons listed there, but none of these seem to apply. The TV is in RGB mode, and the picture displayed cannot be a composite or s-video signal because they simply do not exist in the VGA signal that comes from the PC.

The cable is in the correct SCART socket (there is only one) and manual video format switching is not possible.
« Last Edit: July 05, 2024, 05:25:48 am by asdf015 »

lilshawn

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Re: Black and white picture with VGA to SCART RGB adapter
« Reply #4 on: July 05, 2024, 03:36:05 pm »
it's going to be hard to diagnose without knowing more about... well... everything.

where are you located? north america? south america? china? Europe? Australia?
where did this TV come from? local? imported? USA? Europe? Japan?
what is this TV's normal native signal format? PAL/NTSC/SECAM?
can you switch formats though tv's menu or other such setting?
what resolution are you trying to feed in? is the TV capable of such a resolution? is it too high? is it too low?
what adapter or cable are you using?
what are its capabilities?
is there any configuration that needs to be done to it?

scart can be notoriously difficult to get working properly, and it usually is due to region incompatibilities (50 vs 60 hz signal rates in NTSC vs PAL regions) tv's with specific input requirements (only being able to accept specific types of sync signals) and the "automatic" signal sourcing and configuration by the host device by having specific voltages on specific pins (like pin 8 and pin 16) there may also be incompatibilities depending on the specific revision of scart your TV has and possibly how many scart ports it has. one or more may not be capable of certain resolutions or video signals or sync signals depending on which it has... (as well as a possible difference in capabilities of the various scart ports (if it has multiple, which is not in your case anyway...but i include it for the sake of completion)) not to mention the half dozen types of cables there are and that are meant to be used depending on what kind of connection you are making.) to add even MORE convolution, a tv from japan (even though it has the same 21 pin connector as SCART) has it's own version called JP-21 with it's own pinout. This format was abandoned around 2003 (the same year as your TV's production) so it's not really common.(since your image is black and white and not "red", which is a typical issue when using a regular scart and cable with a JP-21 port... this is also not the case for your issue... but i also include this for the sake of completion)

i guess the first thing for you to do is start at the start of the signal and make sure your computer is outputting the proper resolution and frequency that your TV is capable of...and either switching the signal or your TV settings to match each other (tv service menu?)... as well as the capabilities of the scart cable/adapter or whatever.
(so ntsc/pal 50hz/60hz etc. and so on and so forth.) as long as all the signalling matches appropriately for what the signal is and the scart is telling the TV (via it's config voltages on the 8 and 16 pins), it should display it properly. Pin 8, the switch signal pin, carries a DC voltage from the source that indicates the type of video present.


typically for the switching signals...

for pin 8...
0 V2 V means no signal, or internal bypass
4.5 V7 V (usually 6 V) means a widescreen (16:9) signal
9.5 V12 V (usually 12 V) means 4:3 signal

so you should have 12v on pin 8 to force the tv input to 4:3 mode since your TV is 4:3 format

for Pin 16, (the blanking signal pin), carries a signal from the source that indicates that the signal is either RGB or composite.

0 V0.4 V means composite.
1 V3 V (nominal 1 V) means RGB only.

i'm unsure if having 5v on this pin, as you've indicated, has any negative repercussions.. probably not... but who knows with regard to you particular tv.

your cable or adapter you have should have a circuit to combine the sync signals from your VGA input (Combine RGBHV to RGBs) since the SCART protocol does not support separated sync, only combined or "composite" sync which is a horizontal and vertical sync in one signal. and example is shown here: https://ultimatemister.com/product/ultimate-vga-to-scart/

hope this helps

asdf015

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Re: Black and white picture with VGA to SCART RGB adapter
« Reply #5 on: July 06, 2024, 04:25:36 am »
Thank you for your help and the detailed reply. I am located in Germany and the TV is PAL (it's set to PAL BG/I/DK in the service menu), it also accepts NTSC input.

Just to clarify again, I have two computers set up:

PC 1 (working color, video card with native SCART RGB output that can be directly connected to TV)
PC 2 (black and white, Radeon card with VGA output, connected to SCART over Vga2Scart scan converter board)

On PC 1, I can toggle between NTSC and PAL in the graphics driver, and the TV OSD then shows "50 P AV" and "60 N AV". The colors are working in both modes. I found it interesting that the TV could detect that it's being switched between PAL and NTSC. Isn't SCART completely independent of TV formats? I'm assuming that RGB over SCART does not carry PAL or NTSC signals.

On PC 2, there is no switching between regions, the output is VGA only. I can choose from a ton of different resolutions and refresh rates, such as 240p, 480i, 560i, but none of them has color, even if I select NTSC or PAL resolutions (480i and 576i). The OSD info is also a bit different here, it shows "50 B AV" and "60 B AV" depending on the refresh rate, but it doesn't say PAL or NTSC.

There is no manual switching of inputs and formats on this TV. The remote has a button to switch between TV and AV, but that's it. The service menu doesn't have any options.

I also re-did my multimeter measurements, turns out I had been doing it wrong. The pins need to be measured while the TV is running, because there are termination resistors inside the TV that will drain away some of the current and reduce the voltages to their final level.

Correct measurements of the SCART pins:

PC1:
three column RGB image: 0.20v / pin
single color RGB image: 0.55v / pin
rgb select: 2.7v
sync: 0.34v
status (pin 8 ): 0v

PC2:
three column RGB image: 0.18v / pin
single color RGB image: 0.53v / pin
rgb select: 1.5v
sync: 0.34v
status (pin 8 ): 0v
« Last Edit: July 07, 2024, 01:13:38 pm by asdf015 »

lilshawn

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Re: Black and white picture with VGA to SCART RGB adapter
« Reply #6 on: July 06, 2024, 12:15:35 pm »
Quote
as RGB does not carry PAL or NTSC signals

wellll not necessarily. yes and no.

entire books have been written on how NTSC and PAL work, as well as the VGA standard, and I began to write something out and it would have ended up such a wall of text and you probably wouldn't have understood 75% of it.

NTSC and PAL are less of a "signal" (as you put it) and are more of a specification of how to format your frames and how you tell the monitor or TV to draw them... a series of parameters to adhere to to make it work.

one of those things is refresh rate. the thing that determines refresh rate is the synchronization signal.

NTSC and PAL both use a composite signal for their sync. the use of the word "composite" here is like a material made from plastic and wood... it is that the sync signal comprises of both a horizontal and a vertical pulse in the same stream, a circuit inside called a "sync separator" takes that signal stream and separates the portions of the signal that tell the TV/monitor to move to the next pixel on the scanline (horizontal pulses)... or end the line and restart to the start of the next line down (vertical pulses). (i'm simplifying this a whole bunch.)

the signal coming out of your video card is a separated sync. the video card has 2 wires and 2 signals one that carries the pulses needed for horizontal timing and one that does the pulses needed for vertical timing. RGB scart adapters typically have a circuit to combine the H+V syncs into a composite sync.

so while yes, VGA's RGB does indeed not contain any NTSC or PAL signals... it doesn't really need to... it's just VGA and PAL/NTSC use different forms of the same sync timings.

check your computer's VGA resolution list (you my have to select advanced display settings) and see if you have an option for 59.940hz refresh. (actual NTSC timing refresh rate) and see if you can force it there. windows 10 (which it looks like you are running in your pic) does have some odd timing issues to try (and fail) to increase display and refresh compatibility of old games that were tied to NTSC timings. perhaps this is what's screwing up your video.

you could also try "Custom Resolution Utility" also called (CRU) it will allow you to create custom resolutions and refresh rates and force windows to use them.