I have refurbished my own NES before and have fixed this issue, the problem is a combination of the 72 pin connector and the 10NES chip, which is what is causing the flashing screen, the problem stems from the 72 pin connector, after awhile the pins get bent from being pressed down and over time they begin to stay...
Best answer: I have refurbished my own NES before and have fixed this issue, the problem is a combination of the 72 pin connector and the 10NES chip, which is what is causing the flashing screen, the problem stems from the 72 pin connector, after awhile the pins get bent from being pressed down and over time they begin to stay where they were bent, this is due to general use and leaving the cartridge in for days at a time, but once the pins start staying in that position there isn't a good connection anymore, so this causes the 10NES chip to think there is a pirated game in there so it resets the system over and over causing the blinking red light and flashing screen. If you want a more permanent solution to this problem you can open these NES consoles up, clean and manually bend the pins upward a bit, this will restore the console back to it's glory days for a time, and connection between the console and the cartridges will be more snug and you can play as much as you want without worry. You can also just replace it with a new pin connector, but I find that unnecessary the connector the NES shipped with is much more resistant to bending and is easier on cartridges. By that I mean it won't have a death grip on them and damage them.
A good way of testing if these pins are tight or not is to insert a game but don't press it down, unplug the console leave the cartridge lid open and turn it upside down. If the cart falls out the pins are bad if not, the pins likely still have a bit of grip left in them, probably not much though, unless it was severely unused. Which would be good in your case.
If the pins are not loose enough to bother bending, then just take a cotton swab and some Isopropyl Alcohol (I recommend 70% or higher but 50% will do, just don't get things too wet as 50% wont dry as quickly) and clean the cartridges you have, rub the connector pins until there is no dust or black residue remaining then swab it with the dry side for a bit and let it dry for 10 to 20 seconds and put it in. If it works, great! If it doesn't clean it once more. If you do not have alcohol, you can use just plain tap water, just don't get it too wet as it can get corroded if there is moisture left over.
The NES, even though it has a faulty design, it will never truly fail, unless you neglect it and expose it to the outdoors where moisture can corrode the metal and eat away at the chips and traces.
Another step you can do optionally is to break one of the legs of the 10NES chip, disabling it, the console will never flash a red light again and the screen will remain lit no matter how garbled up the image is. If you are going to go that route I suggest you watch a video explaining it in detail, one wrong move could turn the NES into a paper wieght. But as I said, that is optional.
Cleaning and carefully bending the pins up is a safe and easy method that requires around 10 minutes and a steady hand. And will guarantee that the console will work for a while at least, until the pins bend back out of shape from general use. Also, a Game Genie will speed up that process. It's connector board is a lot thicker than a normal cartridge.
4 days ago