QL display issues

[Traindriver69]

Hi all
I have had a QL since February and the screen display has been bugging me,through the rf lead the picture is bad very fuzzy like it's not tuned in right.
Using the scart lead the picture is spot on lovely and sharp but the display is over to the left hand side by about an inch.
I have tried it on two old school portables and a 50 inch plasma,in monitor mode on the QL you see no text until I have typed in about three characters then the ones typed after that are displayed.
Is this a common display for the QL or have I got one with problems.
Many thanks
Mark

[1024MAK]

In monitor mode, what you describe (via RGB/SCART) is completely normal. The picture within the video signal that the Sinclair video chip produces is non-standard. This is why the start up screen gives you two options. So select TV mode instead , the QL still produces a picture via the RGB monitor port

To see the whole picture when using monitor mode, you either need a old CRT type monitor that was sold for the QL (and has been adjusted/adapted for the QL video signal) or use a SCART to HDMI converter (there is a thread about this elsewhere on this forum).

Mark

[Traindriver69]

But in tv mode the screen is still over to the left but is that normal.

[RWAP]

No, if you press F2 to start up the QL and then type

Code: Select all

PRINT "Hello World"

You should see all of the characters on the screen - TV mode starts with a screen resolution of 448 x 240, with a left & right margin of 32 pixels and top margin of 16 pixels to ensure that you can see it on screen.

For example:

Code: Select all

WINDOW 448,240,32,16 

that will fill the screen on a TV (almost).

Compare that to the full QL screen of:

Code: Select all

WINDOW 512,256,0,0

which is used in monitor mode.

[Traindriver69]

here are a couple of pics to show you what I mean.
also tried typing in the previous post yes with print "hello world" I see all the text but typing in the window ones I see no difference on the screen.
many thanks
mark

[RWAP]

Your QL is working correctly.

The point is that the TV is only able to show a portion of the full QL screen - a lot of games software was written to ONLY use that part which can be seen on the TV mode.

However, a lot of editors and other utilities use the full 512x256 pixel screen which is why in your first photo, you lose the top and left of the screen. There is no way around this other than using an RGB monitor, or using a modern TV with an RGB upscaler (as posted earlier on in the thread).

Try the full QL screen layout:

Code: Select all

WINDOW 512,256,0,0
PRINT "HELLO WORLD"

and compare that with the visible area on a TV screen:

Code: Select all

WINDOW 448,240,32,16
PRINT "HELLO WORLD"

You will note that the second command which will fit fully on a TV screen using a left and right offset of 32 pixels (32 + 448 + 32 = 512) and a top offset of 16 pixels (16+240 = 256)

[Traindriver69]

thank-you for the quick reply that puts my mind at ease over the rgb but what about the rf are they normally fuzzy like its not tuned in right.
cheers
mark

[RWAP]

It depends on what you mean by fuzzy rf output...

Unless your tv has manual fine tuning, it might well be that the signal is not strong enough to lock onto the QL signal fully.

[1024MAK]

Most retro computers (and by this, I mean computers sold to the home or small business user between 1979 and 1990) including the QL use an analogue modulator that uses a RC oscillator circuit.

These produce a modulated video signal at a nominal frequency (normally near the frequency for "TV" "channel" 36).

Because of their design, the frequency is not crystal controlled, so the output is not exactly on the specified frequency for a channel.

Alas some modern televisions assume that you will only use the RF/UHF input to receive broadcast transmissions. Broadcasters use a very accurate frequency reference so that the transmitted channel(s) are as per the allocated frequencies.

If you try to tune in a modern TV to a QL (or other retro computer) and that TV does not feature fine tuning, it will not tune correctly to the video signal sent by the computer

If you have an old CRT type TV, and I mean a inexpensive model, not a top of the range model, try using that with the QL via the RF/UHF lead and see what picture you get.

Using the RF/UHF connection always produces a much poorer quality signal than the RGB output. This is because to generate a RF/UHF output, the RGB signal has to be converted to a composite video signal where the all the colour information, the brightness and the synchronisation signals all have to mixed together. Some picture information has to be cut, because the brightness and colour signals partly interfere with one another. Then the composite signal has to be converted to the ultra high frequency RF/UHF signal. More information is lost, because the width of the signal (bandwidth) of the signal has to fit within the allocated channel frequency range.

Then in the TV, the reverse process is done. By the time all this signal processing has been carried out, and the video is displayed, it has lost sharpness and definition. Where one colour meets another instead of a sharp edge, you get a blurred mess (How bad the result is depends on the actual colours used). Basically it's useless for high resolution multicoloured detail.

Most QL users use the RGB output and ignore the RF/UHF connector.

If you post a picture, we can tell you if what you are getting is normal.

Mark

[XorA]

In retro computers RF has always meant really fuzzy

Its just back in the day everything looked like that and you didn't notice so much!