Atari 130XE Video Problems
As I mentioned in an earlier post, my newly acquired Atari 130XE has some video troubles.
After unboxing it and hooking it up to my LCD using s-video, I saw that the default screen in BASIC is red. It should be blue:
I tried a few games and although they all look OK, you can tell the colors are not quite right.
I am impressed with the overall sharpness, especially compared to my 800XL which does not have the chroma hooked up. With separate chroma and luminance going through to s-video, the picture is nice and clear.
After doing some internet research there is apparently a hole in the bottom of the case that you can use to adjust a potentiometer on the motherboard (R38) to tweak the colors. It was hard to see in the hole but this did not seem to do anything. Upon further inspection, it looks like the bottom of the board where this pot would be is covered in epoxy or something.
I figured I would perhaps try to adjust it from the inside, so I took everything apart to get to the motherboard. I found the pot and tried tweaking it with a screwdriver. But all I was able to do was get it to go from black and white to red.
Looking at the pot, I think it might be trashed.
On Facebook, I got some advice:
Adjust, clean, or replace the R38 potentiometer, 500K. Your pic looks like it was bent somehow. Check to make sure the +5V line is correct. Replace all the elecrolytic caps to be sure.
David W
Another user (Piotr K) included a schematic:
So at this point, it looks like my only option is to try to remove the bad R38 pot and solder in a new one. Considering it is surrounded by epoxy and my soldering skills are non-existent, I don’t trust myself to do this fix just yet.
I think I’m going to practice on something else first, such as a composite video modification for my Atari 2600. At least if I screw that up, 2600s are much cheaper to replace.
If anyone out there has any other tips or suggestions, please leave a comment.
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I don't have anything as useful as what David and Piotr sent you but I am curious about the epoxy, which I assume is the clear looking stuff sort of in a puddle shape around the pot. Is the pot actually soldered in or maybe someone broke it off some how and their repair was to use the epoxy to reattach? A Dremel cut-off wheel might get the pot off the PCB/epoxy. Then unsolder the broken legs out and solder new unit in.