VIDEO DAC BRIGHTNESS ISSUE

[exxos]

Started a new thread as this is getting confusing crossing multiple posts. So please post all info in this thread.

From the Falcon diagram.

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Measuring on my falcon...


Without TV connected...

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With TV connected...

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So we have a DC offset of 0.64V and a max voltage of 2.40V.


Going back to @Icky scopes on the H4..

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I'd say 0.2V min, 2.2V max or there abouts. So the voltages should be fine....

[exxos]

Can someone measure the /BLANK signal and see whats on it ?

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[Icky]

Yep - this is mine

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[exxos]

Yep - this is mine

All looks as it should be them to me

[exxos]

The only change in all this form the V2 DAC board ( I don't think anyone tried the V3 ? ) Was that when we bodged the V2, the analog lines were floating.. I wired them to 0V on the V3 DAC board and H4... I doubt it make any odds (they wired to 0V on the falcon dac) , but I guess if someone could lift those pins up and see what happens...

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EDIT:

I have a theory and I think lifting those pins might actually prove it....

[Icky]

I now have a very dark black screen when the screen should be black, although I seem to of lost my blue line. Need to check my soldering when I was lifting the pins.

[exxos]

Progress you probably need to go back to the default setup with 75R no caps now...

Also can you try and see if there is any voltage on those pins you lifted ?

[Icky]

Yes have done so and we are in business. Lifting the pins and going back to 75R's without caps has worked.

EDIT: Although after looking at that so bright screen now it looks a lot darker. May be a perception thing.

[exxos]

It may not be correct as those pins are floating...but it proves the point...

It needs those 3 lifted pins soldering together.... Then take 10K connected to 5V... then to a 4.7K to 0V (both resistors in series) Then those 3 pins connect to the middle of those 2 resistors... This should bias the pins to about 1.6V.

EDIT:

If you have a 10K pot.. you could use that and manually adjust until the video brightness looks right.

EDIT2:

Or just use a 10K pot.. to 5V one side, 0V the other side, and the center pin (wiper) to the 3 lifted DAC pins.. and just fiddle about with it starting from the center point to get the resistances...

[Icky]

That worked. This was a bit of a hack job but I will clean it up tomorrow and will also compare with original ST to see how it looks.

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