exxos's Atari, Amiga & retro forum

Replace 407 with 22R it will bump the voltage up then measure again..

exxos wrote: 11 Jan 2026 12:47 Replace 407 with 22R it will bump the voltage up then measure again..

I've replaced it and I'm reading 2.32V now, which is only marginally different from the 2.28V I had.

sandord wrote: 11 Jan 2026 17:16 I've replaced it and I'm reading 2.32V now, which is only marginally different from the 2.28V I had.

Try 33R.. You probably just have to experiment, maybe just put a 100R trimmer pot on it and just play..

exxos wrote: 11 Jan 2026 18:47

sandord wrote: 11 Jan 2026 17:16 I've replaced it and I'm reading 2.32V now, which is only marginally different from the 2.28V I had.

Try 33R.. You probably just have to experiment, maybe just put a 100R trimmer pot on it and just play..

I tried and even with 0R, there is not even a measurable difference in the voltage.

Maybe I should shortcut the resistors on the DAC board instead and then replace R407 with a higher value resistor. But I don't know what that will do to the circuit it is part of (R409, R410). Of course I could simply try if that's safe?

Theres really not much to it all..

The 75R on the DAC board is in series with the 75R on the STE. Lowering either value will increase the voltage output.

You then have 75R termination ()or should have) on your monitor which if you have 75R and 75R to GND , then you half the effective DAC output voltage as you have a voltage divider..

Just use a calculator..

https://ohmslawcalculator.com/voltage-d ... calculator

Your source voltage is whatever voltages output directly on the DAC RGB pins..
R1 by default will be 75R + 75R = 150R
R2 *should* be 75R unless something else is screwed up outside of the STE.

Then click calculate and it will tell you the output voltage...

Play around with R1 until you get the output voltage you want, and remember to delete the output voltage from the box otherwise it could screw up the calculation..

EDIT
R409 and R410 shouldn't even be fitted on the STE once the resistor row is removed.

EDIT2:

Looks like R409, R425, R434 should be removed as they be loading the DAC a bit.

Then R407, R420, R432 should be wired linked over.

Then the circuit is the standard DAC circuit then as used on the H5 and Falcon.

Now we're talking!

I did as you told and here's the result:
I wonder if that voltage level is safe for my monitor though?

I took my chances with the 3.42V and it seems to work great with my 1084S-P1 :yay:

I haven't tried it with my OSSC but surely the problem of the low signals is gone.

sandord wrote: 14 Jan 2026 18:02 I took my chances with the 3.42V and it seems to work great with my 1084S-P1 :yay:

I haven't tried it with my OSSC but surely the problem of the low signals is gone.

:thumbup:

The voltage output is standard for the DAC circuit, it is the same on the Falcon and H5 etc.

Thanks for taking the time to investigate, can I steal your image for my website as the mod it may help other users...

exxos wrote: 14 Jan 2026 20:46 :thumbup:

The voltage output is standard for the DAC circuit, it is the same on the Falcon and H5 etc.

Thanks for taking the time to investigate, can I steal your image for my website as the mod it may help other users...

Of course you can! And thank you for developing this great mod and helping me getting it right! :thanksyellow:

Ruh roh... I've been a bit quick to conclude that all is well (typically me) by only judging how the desktop looks.

• When I run a game or something else that doesn't use the default desktop colors, everything dims by 50%. This is most probably caused by GEM setting the extra STE bit on each primary color for its default palette while most programs don't. Normally, this would cause only a very slight variation in brightness (I'm sure nobody notices it) but this is pretty extreme.
• When I run a drawing program that supports STE colors, choosing a color with the extra (4th) bit set, the color intensity is offset by 50%.

Maybe this also explains why I had very dark results earlier, when the resistors were still in place. What a joy when multiple related issues are simultaneously at work, right? :lol:

Anyway, both observations suggest that something's wrong with the 4th bit of each primary color (RGB).

I can't make a picture of the first thing in effect because my phone (like most if not all phones) tend to adjust the overall brightness, which completely cancels out the dimming.

But for the second point, here are a few screen shots from Deluxe Paint, which I put into 4096 color mode.

I created a gradient using STE colors from $000 to $fff, as you can see in the pictures. It should immediately be clear that the palette doesn't look like a smooth gradient but rather a strip of shades with strongly alternating contrasts.