NES Blue Screen refusing to fix

Despite my best efforts, I cannot fix a NES blue screen. What I have done so far:

Swapped out several new and old 72 pin connectors.
Tried games I know work
Cleaned pads on PCB with isopropyl alcohol
Checked connectivity with pins and PCB
Disabled CIC chip

Any other tricks to try out? Of course I could check every trace from the 72 pin connector to where they need to go... I'm just trying to avoid that.

Thanks!

 

Maybe bad CIC chip? It's designed to force CPU to reset if the key doesn't match, which can happen with dirty contact. Even if it's disabled, it can still foul up the system by locking it into reset mode.

Other than that I would think bad CPU or PPU

 

A blue screen, though? I've heard of a grey screen, but the only blue screen I can think of is the default colour for AV input channels on some TVs. So with that in mind, is the TV even changing colour? If not, it could be related to the outputs. Otherwise, you might have screwed up the CIC when you disabled the security lockout. Pictures would help, but could you tell us specifically how you disabled it?

Definitely try cleaning and cleaning the 72-pin connector contacts and the cartridge contacts, though. That often makes a difference. Hell, if it still doesn't work, just blow on it. I know blowing on it isn't a good idea, but if it's not working anyway, you may as well try it. Sometimes it actually helps. Of course, there are much better ways to clean the contacts, but as an absolute last resort, you can try it (and if it works, clean the contacts again with isopropyl alcohol to try to avoid corrosion).

 

First, the NES had the blue screen when I got it. Someone may have tried to repair it in the past, but it looks like everything is intact.

The screen is a solid blue. No flashes or any other color change. I disabled the CIC by pulling out the 4th pin from the chip, after reading extensively on how to do it.

I'll check the traces to the RF box to make sure nothing is broken there. I might also reflow the solder for the CIC chip, see if that does anything.

 

Capacitors?

 

Sometimes my NES was green or gray before I did the CIC mod. It might just be either dying chips or old, dry capacitors.