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Composite mod, picture too bright

Started by mrdremel, March 17, 2024, 09:48:16 AM

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mrdremel

Hi all,

Found this site while researching my "issue" with my newly acquired G7400. My G7400 was non-functional. Powersupply broken, switch broken and RF converter non-functional.

I replaced the powersupply with a modern 5/12 volt powersupply. It even fits in the case. I have bypassed the power switch for now and will fix it later. The good news is....I resurrected this dead G7400 :-)

However, the RF converter had such a weak signal that it is useless. I have the Dutch version, so no RGB components.

I tried a direct composite line from the mainboard to my tv. The signal was way too weak, but is working.

I added the Atari 2600 composite mod. I now have picture, but it is so strong that it is too bright and the colors are not clear enough.

Question:
Can I add a resistor to the output line to make it a little bit weaker? I can solder and tweak just fine, but have too limited electronics knowledge. Does anyone have any experience with this?

Xuul

Hey,

so this G7400 composite mod doesn't work with the Dutch version?

Xuul
Programmers don't die.
They just gosub without return.

mrdremel

Quote from: Xuul on April 03, 2024, 12:31:33 AMHey,

so this G7400 composite mod doesn't work with the Dutch version?

Xuul

The mod I use is the same. The circuit for the video signal uses the parts listed here.

But the video signal seems too strong. That is why I wanted to ask if I can make it a little bit less strong by for instance adding a small resistor.

Xuul

#3
Quote from: mrdremel on April 08, 2024, 11:22:23 AMThe mod I use is the same. The circuit for the video signal uses the parts listed here.

But the video signal seems too strong. That is why I wanted to ask if I can make it a little bit less strong by for instance adding a small resistor.

I've modded a bunch of G7400s with that mod, and the picture was always clear and the colors were fine.
I've also modded a couple of Atari 2600 Jr., but the mods I used required different components, not the ones used for the G7400 composite mod.
So you are using a BC547B and a 220 Ohm resistor? Also, check the solder points on the board again, maybe you are grabbing the signal from the wrong locations?

You could try and replace the 220 Ohm resistor with a potentiometer and see if you can find a value that gets you a better picture.

You wrote you replaced the internal 12/5 V PSU with a custom one. Where did you get that? Do you have a link?

Xuul




Programmers don't die.
They just gosub without return.