exxos's Atari, Amiga & retro forum

Icky wrote: 15 Dec 2019 23:47 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.

Cool. Looking a lot better now!

I now need to try it out on the monitor that had complete whiteout now to see if that has changed.

Congratulations and well done fixing that issue!

I've done the circuit tweaks on the REV F.



So what I think was happening before, when those three lines were hardwired to 0V, is there is probably some sort of AGC in the monitor where I assume it would adjust the black level to the correct voltage. In this case it would ramp up 0V to 1.6V to get the correct black bias voltage. But in doing that, it would also ramp up the RGB brightness by another 1.6V basically making it twice as bright as it is supposed to be.

So what we do now, is Bias the black level at 1.6V so then the AGC in the monitor has no reason then to adjust that voltage, or end up adjusting the actual RGB brightness as a side effect either.

This is what made me think about this in the DAC datasheet..

Icky wrote: 15 Dec 2019 23:47 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.

Icky, it looks like you didn't lift the pins? How did you sever the ground connection?

PaulJ wrote: 16 Dec 2019 15:13 Icky, it looks like you didn't lift the pins? How did you sever the ground connection?

It must be a trick of the light @PaulJ. Legs are definitely lifted and level so as to be used as a platform for the resistor legs.

I've been a bit lazy and did the @Icky method and skipped the cap.

Works for me

Icky wrote: 16 Dec 2019 18:45

PaulJ wrote: 16 Dec 2019 15:13 Icky, it looks like you didn't lift the pins? How did you sever the ground connection?

It must be a trick of the light @PaulJ. Legs are definitely lifted and level so as to be used as a platform for the resistor legs.

@Icky I was afraid of that. Looked at the layout and couldn't come up with a patch without lifting the pins. Thought you had performed a miracle and clipped the multiple grounds some how. Guess I'll have to summon up some courage and give it a try. :mrgreen: :mrgreen: :mrgreen:

PhilC wrote: 16 Dec 2019 20:31 I've been a bit lazy and did the @Icky method and skipped the cap.
Works for me

Nice picture @PhilC , looks great. How about a picture of the patch. :?: :?: :?: I trust you're still using the 75 ohm resisters?

Mines a bit of a bodge @PaulJ as I've not got and SMT 75 ohm resistors, so I've fitted 3 axial ones but still it gets the job done just fine.