So, I have a stack of NES units, and I'm trying the various ways to get one to work well. I've swapped out connectors many times, it rarely improves it that much.
I have a box of new connectors, a box of old connectors, a stack of NES units. I have a stack of clean games that are very common (SMB, SMB/DH, SMB 2/3, Double Dribble, Ice Hockey).
I'm also playing with the lockout chip.
Things I've tried:
1)
New connector only. Not all that much improvement, did improve some, didn't get anywhere near 100%, makes it really hard to get the cart in and out.
2)
Cutting pin 4 on lockout chip w/old connector. No blinks, now it's mostly a grey screen when the cart doesn't work. No real improvement.
3)
Cutting pin 4 on lockout chip w/new connector. A little improvement on some games, none on others.
4)
Grounding pin 4 on lockout chip w/old connector. Same as without pin grounded on old connector. The connector is mildly clean and seems to perform the same with or without lockout chip.
5)
Grounding pin 4 on lockout chip w/new connector. No better than with old connector.
So, at this point, I'm stumped and annoyed. Disabling the lockout chip gets rid of the blinky screen but replaces it with a dead grey one. The new connector made a small difference but not an acceptable one.
Just to really knock this one down, I busted out the SMB/DH I got in a lot of NOS NES items a while back... literally, never been played. Pristine. Acts no different than the rest of the games, boots probably 25% of the time.
I've tried a new and old connector, tried both versions of the lockout mod, and tried regular wear games as well as a NOS game. All act roughly the same, unaccpetably.
The only thing left to try is to do this to a couple more NES units and see if the results are the same.

(I'll keep updating this post as I progress through the scenarios, feel free to comment as it goes)