SNES Generation 1 Video Problems, 50+ Units with same defect. RF Works Fine, RCA Output BAD

[neojapan]

HI Guys, been in the videogame repair business for 15 years, but never figured out how to repair the Model 1 Super Nintendo that has AV Problems, so I just kept storing these up, so I am fed up with all these defects here, and need help to figure out whats wrong with them! and no, its not cap replacement, Ive done enough cap replacements on my snes to know this is not the problem!. Ok so in a nutshell, all of them are Generation 1 SNES Consoles, the one with the removable soundboard, all of them work fine with RF Hookups but if you use an AV Cable a lot of jitter can be seen (And you can hear the sound ok) So I guess the snes has 2 video controller chips, of some kind, that outputs the video one thru RF and the other thru RCA. I need to know which chip is it! and its damaged on all of my 50+ consoles, (95% of generation 1 snes that i get i trades have this damn problem).

I guess is a progressive damage that occurs over time to a particular chip
Some Consoles start showing dark image on RCA, normal image on RF
Some Consoles start showing dark image on RCA then Starts to Scroll and image fades, normal image on RF
Some Consoles start showing black and white jittery image on RCA, normal image on RF
Some Consoles start showing black screen with some lines waving (No Image) on RCA, normal image on RF

Full Cap Replacement has no effect

any feedback is greatly appreciated. Thanks!

[RP2A03]

Looking at the schematic, composite and RF originate from the same point. This leads me to believe one of the following is your problem:

1. Your cables or TV composite jack are bad
2. Composite video pin on the multi-out is dirty or corroded.
3. Something is bad in the circled area of the schematic. Check your grounds as well.
4. The composite signal coming from the video encoder is bad, but the RF modulator is able to correct it.

This is technically for a revision 2 board, but the idea is the same. Click for bigness.

[Bratwurst]

Given the description that full cap replacement doesn't fix the problem, I'm leaning towards the video encoder, in this schematic's case the BA6592F. That or the Q10 transistor.

[Niku-Sama]

if at all possible I would tap into the 6592 directly and see if you get any thing there, if not then you'll rule out trying to find something between there and the plug.

also isn't the 6592 the one labeled S-ENC some times? you could see if you get component video off of it if its the same as the S-ENC's and maybe find if a particular channel has gone bad (y, pb, pr) or something

[RP2A03]

if at all possible I would tap into the 6592 directly and see if you get any thing there, if not then you'll rule out trying to find something between there and the plug.

also isn't the 6592 the one labeled S-ENC some times? you could see if you get component video off of it if its the same as the S-ENC's and maybe find if a particular channel has gone bad (y, pb, pr) or something

Remember that his trouble is with composite video. Since RF works, we know that the video encoder is outputting a composite signal. I would expect the problem to be in the video amplifier, most likely the transistor as suggested by Bratwurst.

[neojapan]

Thanks everyone for the replies, I tapped into the video encoder directly, Red and Blue, I got green from pin 7 as in this picture:



But it didnt display anything so i just got green from the encoder directly, unfortunately colors show almost black and white, but its showing picture



I'm yet to try and replace Q10, ill try that later, but what you guys think? why are colors showing like this? thanks again