After a little looking around I decided to do this simple mod here
. The values were strange but after a while I found combinations of resistors (using serial and parallel combinations) I have to give me the exact values that were called for. I double-checked the values of each set of resistors, and combined them as seen in the schematic with a 2N3904 transistor (not the exact transistor used in the schematic, but I figured it's close enough and doesn't matter).The problem:
the resulting video is totally unstable and messed up. It scrolls (the whole thing moves from top to bottom and then repeats), looks like each successive scan line is not lined up to the next (so vertical lines that are supposed to be vertical are definitely not), there's no color, and I'm not completely sure everything is even there.Guesses and what I've done:
The only thing I can figure is that it has something to do with the fact that I didn't do the previous step of modding the board into the 4x4 form, meaning something about the board is different than what the mod I read started with. However, I did remove the RF modulator from the circuit. Later I tried removing the small set of components just above that (C214, C213, L205, and C212), but that made me lose the signal completely, so I put them back. I don't see what else could be different between the two forms that have anything to do with video and would therefore make a difference. (I have the type A board btw, and did follow the directions for that.)
I've also removed the center pin of the transistor just above the tuner (tall, red, adjustable thing. as recommended by aforementioned tutorial. removed prior to testing), and the tuner itself (not mentioned at all in tut. removed after testing, with no change).
I've triple-checked to make sure everything is connected to where it should be. There are no visible shorts. Nothing was soldered directly to the TIA pins, to avoid risk of damaging it. The +5 volt source is good (although it doesn't appear that could be the problem anyway). I tried connecting the composite lead to before the transistor, and the signal is already messed up by then. Adjusting the color pot does nothing. Could it be I just have a different board which would require different resistances?? The game I've been testing is Frogger (which worked before I began), and I'm on a standard CRT.
If I can get a hold of a camera I can take some pictures. To be honest, I think I did a pretty good job on a point-to-point construction of the circuit (stemming off the original board), with good solder joints, so I don't think the construction job is the problem. Hopefully somebody can help me or has some ideas. Any help would be very much appreciated. What do you think?
(also, please let me know if there is a better place to post this)