Video driver thoughts

[Icky]

@ Icky, I wonder if you can try the normal RGB circuit, but lift out the BLACKing didoes D1,D2,D3 ?

Just in the process of getting the video uploaded of the motherboard driver circuit in play.

Then I may get time to lift the blanking diodes - non-Atari duties are calling tonight.

Well I did say it was dark - didn't realise how dark until I filmed it

[exxos]

Who is awesome

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[Icky]

Who is awesome

Exxos is awesome - How did you do that

[sandord]

Who is awesome

IMG_3622.JPG

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It's Chris Norris!!

[exxos]

Exxos is awesome - How did you do that

I lifted that highlighted pin which, and linked to small wire from it to the BLANKing line...

So when BLANK is high, it selects D-RGB mode, when BLANK is low it selects A-RGB mode...

Technically the A-RGB lines are floating, but at this time of night I did not care, and it works anyway so

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[Icky]

Exxos is awesome - How did you do that

I lifted that highlighted pin which, and linked to small wire from it to the BLANKing line...

So when BLANK is high, it selects D-RGB mode, when BLANK is low it selects A-RGB mode...

Technically the A-RGB lines are floating, but at this time of night I did not care, and it works anyway so

Brilliant so it was blanking related

Question now is to compare original circuit against new DAC circuit to see improvement.

[exxos]

Question now is to compare original circuit against new DAC circuit to see improvement.

Sadly it looks the same

Mostly I was trying to get rid of the vertical noise lines in the drag bar but they are still there... Only now they seem to be flickering a little bit...

I do have some 40R resistors in series with the RGB outputs with 47pF on them.. so its not like its noise there...


Gave myself permission to upload a high res shot to illustrate this...

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The thing is, I don't think I saw this on the Falcon video.. and its the same chip now

BTW - the jumper does up the brightness a little, not a great deal...

[stephen_usher]

So, is this a similar issue to the “front porch”/“back porch” video generation issues that the early ZX81 ULAs had?

Basically in that case the ULA didn’t produce a “back porch” on the video signal so the TV/monitor circuitry couldn’t determine the base level of the signal. In the case of the ZX81 color TVs took the “white” level to be black and dimmed the display accordingly.

I guess that in this case the monitor could be taking a floating value as the black level, when the border is white. When it’s black then it emulates a back porch.

[PhilC]

Well done guys. Looking better and better.

You'll get there with the quality thing Exxos, just take a bit of tweaking is all.

Will lift the pin tomorrow and catch up yet again, lol.

Still didn't fix the floppy drive problem, too busy with Fallout 76.

[stephen_usher]

Question now is to compare original circuit against new DAC circuit to see improvement.

Sadly it looks the same

Mostly I was trying to get rid of the vertical noise lines in the drag bar but they are still there... Only now they seem to be flickering a little bit...

I do have some 40R resistors in series with the RGB outputs with 47pF on them.. so its not like its noise there...


Gave myself permission to upload a high res shot to illustrate this...


IMG_3626.JPG


The thing is, I don't think I saw this on the Falcon video.. and its the same chip now

BTW - the jumper does up the brightness a little, not a great deal...

It looks like your display is doing a great deal of “sharpening”. Lots of nasty halos!