I just got done doing a composite mod on an atari 2600 and thought I would go over some issues incase anyone else experiences the same problem I had.
Instead of getting the parts and doing it myself I figured I'd just buy the kit because it came with everything plus has a nice looking PCB and also it was about as cheap as me getting all the parts separately but here is the mod kit I got http://www.ebay.com/...V0AAOSwnbZYHzc7
I bought two of them and will be modding another 2600 to compare and post back the results.
Well to start off with I bought a GPX KCLD8886DT under cabinet TV to put at my work bench thinking it would make a good TV to test consoles. Well I hooked up my atari flashback in thru AV and everything was fine, it looked perfect. Then I hooked a Vader 2600 to it thru RF and looked normal for RF.
I did the mod upgrade with the kit and then I hooked it up to that same TV but this time thru AV since mod was done and sound was perfect but had no picture. I kept checking around the board looking for loose solder joints then wiggled the wires right near the ground, +5V and video signal where the RF board used to plug into. The picture came on and looked fine. I'd turn off the console and start it back and same issue again so then I'm thinking I must have a bad solder joint. I look at it real close both sides of board solder looks fine. I reflow it anyway. Still same problem. So then I check the +5V with my oscilloscope, and video signal and used the ground right there first pin for my ground incase the ground was broke somewhere one the board. Everything looked fine I had a video signal there and +5V. Then I look at the video signal on the output and I had a video signal there but still no picture.
After scratching my head for awhile I decided to try the Atari 2600 on another TV. Picture perfect(other than some fine vertical jailbars but looks like all the composite modded consoles I've seen pictures of online have that). Took it back to that GPX TV and still had same issue. I figured by that point the problem is that the signal wasn't amplified enough for the GPX to recognize it as a signal so therefore blue screen, and what was happening was I guess when I was wiggling wires and probably touched the video signal and it caused a signal to go up high enough to trick the TV to display the picture.
So I decided to show the comparison of the two video signals incase anyone runs into the same problem.
I'm including pictures of two separate video out signals with space invaders plugged in. The stronger of the two is the flashback which plays fine on the GPX. Very disappointing because the sole purpose of me getting this TV was to have something small at my workbench and be able to test consoles on. I guess I'll have to get or build a separate amplifier now to plug consoles in that don't have a strong enough video signal. My appologies for the poor picture quality, I took some too with an Iphone but couldn't find the cord and have no service here so couldn't email them to myself so I had to take them with my junk phone. I might try to upload the higher quality images of the scope tomorrow once I can email the pics to myself.
My biggest concern with doing this mod if doing for other people is not knowing who's TVs this will work on and who's it will not so I think I will change some values and try to get it to more closely resemble the amplitude of the flashback unit. I'm going to wait first until I do another mod and make sure the other 2600 also has a weak signal like this one to make sure it isn't anything I overlooked with this console but I don't believe there is.
If anyone has any questions or comments about this let me know.