I have an NES that was giving me a blinking red light when powering up. I had chalked this up to the 72-pin connector and set about cleaning it. After cleaning the connector and all games, the problem persisted. I replaced the connector with an aftermarket one, with the same result.
At this point, I assumed it was the 10NES chip, and cut pin 4. Now, when I boot, I just get a blue screen, with either the original 72-pin or the aftermarket.
EDIT: Its most definitely not the TV, I've tried it on two different CRT units, both of which work fine with other older, composite output based consoles.
I have also tried another AC adapter. Like I mentioned originally, it was working, just not reliably.
RF output also produces the same result.