nes with video issue

[crazzywolfie]

the other day i picked up a nes very cheap. i figure it just needed the basic 72 pin connector cleaning and tweaking and it would be working fine again. now the picture on screen usually displays fine for about 1-2 seconds then kind of mess up and go black and white. i have been googling to try figuring out how to repair it but not finding much. i have narrowed it down the RF modulator in the nes because if i hook the video wire to the composite pin on the nes's main board i get a clean picture but i don't get get it at the normal composite output on the RF modulator. i have been googling trying to find a solution but not come up with much which. any help would be appreciated.

[Niku-Sama]

sounds like a bad cap or a component getting too hot on that output in the shielded box. probably best to de solder the box and tap directly into the board. that way too you can feed a direct DC voltage too

[APE992]

sounds like a bad cap or a component getting too hot on that output in the shielded box. probably best to de solder the box and tap directly into the board. that way too you can feed a direct DC voltage too

Bad caps generally don't cause B&W pictures, loss of color data would but the fact he can tap the composite signal elsewhere suggests a cap isn't working correctly to begin with. My NES had bad caps that showed up as a lack of audio amplification. AT this point all of them likely have dried up in all consoles, replacing them is a solid start.

I'd scope the signal out to verify. The fact it starts in color is a good sign.

[Niku-Sama]

Considering the op has clean composite at the main board but not off the shielded box on either output suggests to me we can skip the scope and get right to digging. In all honesty I'd remove the whole thing and tap the composite, audio and wire up a barrel plug to the voltage lines with the proper voltage reg circuit and just use a dc power supply instead of the AC 9v one the nes normally uses.

I've seen my fair share of caps causing odd problems. I'm sticking to my suggestion on that being a possibility in this case as I've seen some on video lines fail and cause all sorts of distortion but I'm thinking it's a probable cause. Not the most probable but something to take into account.

I'd imagine it's something else getting hot/shorted over a cap.

Thinking about it now I'm wondering if the composite straight from the board is dim at all

[Bratwurst]

Bad caps generally don't cause B&W pictures,

Yes they do. I've fixed Sega Genesis systems putting out black and white video by replacing caps.