kodak80 H4 build (x2)

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PaulJ
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Re: kodak80 H4 build (x2)

Post by PaulJ » Sat Dec 14, 2019 10:39 pm

I haven't stated on my second one yet. I'm going to give the SMT glue and mmu a try which have not arrived from Exxos's store yet. Need to do a majority of the SMT prior to installing all the other components. Good luck on your second. :) :) :)

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Re: kodak80 H4 build (x2)

Post by kodak80 » Sat Dec 14, 2019 11:19 pm

exxos wrote:
Sat Dec 14, 2019 2:25 pm
:bravo: try those big smt caps in series with the 75R like @PhilC did and see if it solves the issue.
Video output is still washed out but slightly improved. Currently have 220R resistors and the Alpha DAC large capacitors in series.

Monitor is reset back to mid range for brightness and contrast.

Thinking that larger resistors, (470R?) would still improve things. I don’t want to damage anything though.

Also, does it make a difference which side the extra capacitor is with the resistor? I currently have the caps after the resistors in series.

Original with no caps and 150R:
F5123F23-0ECB-4B4E-9485-34273C5D67B7.jpeg
F5123F23-0ECB-4B4E-9485-34273C5D67B7.jpeg (207.01 KiB) Viewed 435 times
Current, with caps and 220R:
5EC5D0C2-3257-49B2-B05F-643EA49B86EB.jpeg
5EC5D0C2-3257-49B2-B05F-643EA49B86EB.jpeg (244.23 KiB) Viewed 435 times
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Re: kodak80 H4 build (x2)

Post by exxos » Sat Dec 14, 2019 11:35 pm

Based on a input voltage to the RGB of 3.315V and assuming the monitor has 75R load and 0.7V max output, then the resistor value would work out at about 280R. So probably 330R would technically be about correct to get the voltage levels to max of 0.7V.

I don't suppose anyone has a falcon they can scope the videl to DAC MSB lines to see if they pulsing ?

The MSB DAC bit if not used would give a max output of 1.6575V which is still to high.. 2 bit less would be 0.82875V.. But as the Falcon has 75R series resistance and assuming 75R monitor termination, then is a /2 voltage divider, so bit 7 on the DAC can't be switching on the falcon, otherwise the brightness would be maxed out.
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Re: kodak80 H4 build (x2)

Post by kodak80 » Sun Dec 15, 2019 12:41 am

exxos wrote:
Sat Dec 14, 2019 11:35 pm
Based on a input voltage to the RGB of 3.315V and assuming the monitor has 75R load and 0.7V max output, then the resistor value would work out at about 280R. So probably 330R would technically be about correct to get the voltage levels to max of 0.7V.
With caps and 330R there is no real improvement over the 220R resistors.
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Re: kodak80 H4 build (x2)

Post by exxos » Sun Dec 15, 2019 12:43 am

kodak80 wrote:
Sun Dec 15, 2019 12:41 am
With caps and 330R there is no real improvement over the 220R resistors.
Can you scope the voltage on the one of the RGB lines ? it should be switching between 0V and 0.7V.
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Re: kodak80 H4 build (x2)

Post by kodak80 » Sun Dec 15, 2019 1:19 am

exxos wrote:
Sun Dec 15, 2019 12:43 am
Can you scope the voltage on the one of the RGB lines ? it should be switching between 0V and 0.7V.
I am still figuring out my scope software so not sure if this is of any use?
dac-rgb.png
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dac-rgb2.png
dac-rgb2.png (57.07 KiB) Viewed 412 times
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Re: kodak80 H4 build (x2)

Post by exxos » Sun Dec 15, 2019 1:23 am

kinda looks like about 2.5v...

Turn your monitor off and unplug the cable and measure resistance on the red pin.. The monitor should read 75r ... If it doesn't, then it would explain a few things.

In which case we may need to add the 75r as a voltage divider to reduce the voltage.
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Re: kodak80 H4 build (x2)

Post by kodak80 » Sun Dec 15, 2019 1:38 am

With the computer and monitor turned off with monitor still connected I see a fraction over 75R on the red.

With everything off and the monitor connector unplugged, I get what looks like a capacitor charging (3.xx and increasing) reading on my multimeter when testing the same rgb point as the 75R reading above. Tested against both GND and 5V with same reading.
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Re: kodak80 H4 build (x2)

Post by exxos » Sun Dec 15, 2019 1:40 am

odd... 330 and 75r is about 0.6v so the image should be a fraction to dark if anything .
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Re: kodak80 H4 build (x2)

Post by kodak80 » Sun Dec 15, 2019 1:42 am

Sorry, I have not added the 75R voltage divider in. Not sure where this would go?
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