The Sinclair QL Forum

During some tests of my new collection member I recognized some screen noise but only when using microdrives.

You can see it if form of some small black stripes being shown randomly on the screen (it was difficult to take a picture of them because they vanish; on the screenshot you can find an example under the letter "n" in the word "Kalkulation" when loading Abacus).

What is the reason of this problem? It is a naked DE QL, with no modifications (regardless new keyboard membrane) and no extensions.

Is that with the QL-VGA? If so, I get those random black marks too, but I must admit I hadn't associated it with the md. It's so random and so rare that I didn't bother Marcel with it.

Chr$ wrote:Is that with the QL-VGA? If so, I get those random black marks too, but I must admit I hadn't associated it with the md. It's so random and so rare that I didn't bother Marcel with it.

Good point, I used the QL-VGA indeed. However my other DE QL does not have these symptoms. Strange, but good to know I'm not the only one

Never mind all that worrying about a few black marks on screen, I want to know what's behind the monitor!

I see a soldering station (I have a cheap one coming from Amazon today, cheap but a 5* review so it should be fine for my needs), a few storage boxes, an air duster but what other goodies do you have hidden there! Oh yes, and a pine code!)


Cheers,
Norm.

grafvonb wrote:

Chr$ wrote:Is that with the QL-VGA? If so, I get those random black marks too, but I must admit I hadn't associated it with the md. It's so random and so rare that I didn't bother Marcel with it.

Good point, I used the QL-VGA indeed. However my other DE QL does not have these symptoms. Strange, but good to know I'm not the only one

Well, I cannot imagine how QL-VGA could produce these artifacts in the middle of the screen, as I do double buffering, but of course I cannot rule it out either. Would be interesting to know if the same phenomenon happens using a SCART connection or whatever.
I do have occasional stripes likes these with one QL, but these stay and don't disappear again. Some strange interaction of the (S)GC corrupts the internal RAM copy of the screen. But these happen with a a normal monitor, too.

I also see stuff like that, but have never seen it on an unexpanded QL. As Marcel says, it seems to be a loss of alignment between the SGC video shadow and the "real" video memory in the QL.

Can you run the Minerva memory test on this QL? It nearly looks as if the video memory on that machine is flaky.

Tobias

mk79 wrote:

grafvonb wrote:

Chr$ wrote:Is that with the QL-VGA? If so, I get those random black marks too, but I must admit I hadn't associated it with the md. It's so random and so rare that I didn't bother Marcel with it.

Good point, I used the QL-VGA indeed. However my other DE QL does not have these symptoms. Strange, but good to know I'm not the only one

Well, I cannot imagine how QL-VGA could produce these artifacts in the middle of the screen, as I do double buffering, but of course I cannot rule it out either. Would be interesting to know if the same phenomenon happens using a SCART connection or whatever.
I do have occasional stripes likes these with one QL, but these stay and don't disappear again. Some strange interaction of the (S)GC corrupts the internal RAM copy of the screen. But these happen with a a normal monitor, too.

I don't remember seeing it with a GC and a composite vid display, but that was setup to b/w so it probably wouldn't have really been that noticeable. Now I'm running an SGC with the QL-VGA. It really doesn't bother me though, whatever the cause. I'll put it down to (S)GC freakiness then and will let you know if it worsens/changes.

mk79 wrote:Well, I cannot imagine how QL-VGA could produce these artifacts in the middle of the screen, as I do double buffering, but of course I cannot rule it out either. Would be interesting to know if the same phenomenon happens using a SCART connection or whatever.
I do have occasional stripes likes these with one QL, but these stay and don't disappear again

Using SCART the problem remains however the stripes became almost full lines. So it is not a problem of the QL-VGA...

grafvonb wrote:Using SCART the problem remains however the stripes became almost full lines. So it is not a problem of the QL-VGA...

That is a relief, thanks for checking Still cannot quite imagine what could cause this. But this effect is only for a single frame and then disappears again? As you said it's a German QL I guess it's an issue 6 and on these the ZX8302 that does the MDV stuff is not on the same data bus as the ZX8301, which makes this even stranger...