ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hello,
It may seem ridiculous in this day and age, but I am trying to feed a RGBs signal to a BC1 on the AV Scart declared as a STB.
I am using a Kramer VP-101 to convert a VGA signal. I have built a Scart cable with RGBs and Audio L/R (plus all the corresponding ground).
Unfortunately it's not working. The screen is grey/white with a sort of rolling signal that 'moves' down the screen.
When I look in the service menu, i see basically two errors :
I have tried a bunch of different output resolutions with anything but the grey/white screen.
My first though is that for some reason, the BC1 does not recognize that it has a RGBs signal on the Scart input and the artifact that I seen on the screen is because it is reading the sync signal as composite video.
So, is there anything that needs to be done to set the Scart to RGBs ?
The other thought concerns the RGB status on pin16. I never could figure out what is is, so there is nothing there. I hoped that no signal would correspond to 0v/75ohn, "Internal", whatever that it means.
Thanks for any and all help !
- Scott
I believe your biggest problem is that the BC1 is strictly a TV, not a monitor. Therefore it will not be able to show a non-interlaced VGA signal even if you convert the signal levels and sync types. The Kramer box is a signal converter, not a format transcoder, so you will need to coerce your source to output an interlaced, 576 active line 50 Hz signal a PAL TV would be expecting. I believe that's why your image now keeps rolling over.
Then, the BC1 input in RGB mode will expect to receive a video level composite sync signal on its composite video input pin (a composite version of the actual video with sync will do). The Kramer device seems well able to do that. If you just disconnect the R, G and B lines, you should see a black steady picture frame.
And finally, the pin 16 will indeed need a signal voltage so that the BC will know it is supposed to work in RGB mode. I'm not familiar with that particular TV but I believe it is the same with most other B&O TVs, i.e it doesn't have any menu item or function that allows you to force it.
--mika
Thanks for your reply.
I am using SwitchResX to generate an interlaced signal over MDP->VGA to the Converter. You confirm my fears that pin 16 needs a signal.
I am very much an electronics beginner, any good ideas on how to generate a 75Ohm signal ? Would it be sufficient to simply double the Red signal for example ?
Scott Needham:I am using SwitchResX to generate an interlaced signal over MDP->VGA to the Converter.
OK, then I believe that part of the problem is solved already.
The pin 16 signal is just a switching voltage, supplied by the external device to the SCART. It needs to be between 1 to 3 volts to switch the input to RGB mode. The "75 ohm" is the input impedance of the SCART pin, in this case you can think of it as a 75 ohm resistor connected from the pin to ground (inside the TV set).
I guess that as a quick test, you could supply the switching voltage from a 1.5V battery (positive pole to pin 16, negative to video ground). This is not a good solution as the battery won't last too long, but if the result works we can think of something more permanent.
This page has more info - as your source is a computer, it might be possible to steal the switching voltage from a spare USB port with a couple of resistors to divide the voltage down from +5V.
Excellent !
I will give it a try this weekend.
I also found a table where pin16 is labelled as
This is a lot more explicit than the information on BeoTech and confirms the behavior of my TV.
Thanks again !
Hello again,
I have tested this evening and can state that this indeed is the solution. :-)
I can also confirm that the USB idea works as well !
Now on to the next challenges ...
I am using SwitchResX to generate an exact signal on the HDMI output (576i50). It is passed to a HDMI-VGA converter and then to a VGA-RGBs converter. Neither of these devices does any scaling.
Strangely enough, the picture seems too big. When I look at the desktop of the Mac, the top bottom, and sides are all missing a little. When I launch Plex I can adjust the overscan, but is this really wise for the picture ?
Plex also introduces other artifacts, little green pixels on dark areas of the picture that are especially visible around the borders of the image.
Very strange. I would appreciate any ideas !
I am also looking for the exact horizontal and vertical timings (front porch, back porch, pixel clock, etc ...) if anyone knows where such a thing can be found.
Good to hear you got it working
Regarding the too big picture, that is quite normal for a CRT TV. Because the physical picture size cannot be adjusted exactly, they extend the picture (and often the actual picture tube as well - it's never exactly rectangular) beyond the area that is visible to the user. A user watching regular TV transmissions would complain loudly about non-straight picture edges or black stripes. TV production takes this into account with a so called safe area - everything important in the actual picture frame is kept inside a smaller rectangle, about 5% off each edge (although lately, more and more graphics designers are forgetting this...).
Computer monitors don't have this problem and use the entire display area for the desktop. What this means to your task at hand is that you cannot get all 576 lines visible on the screen unless the BC1 can be switched to underscan mode. Optimally, you would want to disable interlacing as well to reduce the flickering of vertically small objects. I believe at least the latter is possible on later MXs with some "secret" remote command, so it might work on the BC1 as well - perhaps somebody remembers it?
* * *
I believe these pages contain all the timing information:
http://www.pembers.freeserve.co.uk/World-TV-Standards/Line-Standards.html