How to troubleshoot, diagnose and repair Nintendo NES common problems

How a Nintendo NES game cartridge looks in the 72 pin connector
Nintendo NES Toaster
Nintendo NES Toaster

A very common problem for the original style “toaster” NES is when you put in a game and turn on the NES that you only get a blinking red power light and the system won’t play the game…This symptom can be caused by multiple factors so lets first understand what’s really going on here.

Nintendo installed a lockout chip (also known as the C.I.C. Chip) on the motherboard of the toaster NES. Note: The newer style “Top Loader” NES does NOT have a lockout chip on the motherboard. Nintendo implemented the lockout chip to try to stop non licensed games from being produced for the NES. Because of this lockout chip every officially licensed NES game has a chip in the game cartridge that syncs with the NES’s Lockout chip when you turn on the NES. When you turn on the NES the lockout chip on the motherboard looks to sync with the game chip. If the game doesn’t have the chip present the NES will then restart once every second because it “thinks” you have a non licensed game. Now that you understand the lockout chip and how it works you can better understand how to fully diagnose the NES.

Nintendo NES Motherboard Version 10 from 1987
Nintendo NES Motherboard Version 10 from 1987
NES Motherboard with Lockout CIC Chip Highlighted
NES Motherboard with Lockout CIC Chip Highlighted

It’s pretty simple to disable the NES lockout chip. You need to open up the NES and get it down to the motherboard. I’ve attached a picture for you to see where the lockout chip is located on the NES motherboard. All you need to do is cut pin 4 on the lockout chip. The way I cut it was by using a pick tool (looks like the one a dentist uses to scrape your teeth). All I did was pull pin 4 out of the chip and viola! No more NES lockout chip! Once you do this your NES will not restart once every second if you don’t insert a game.

Nintendo NES Motherboard after Lockout Chip (CIC chip) has been cut
Nintendo NES Motherboard after Lockout Chip (CIC chip) has been cut
NES Lockout CIC Chip Close Up View
NES Lockout CIC Chip Close Up View

Repair Nintendo Problems

Another common problem with the NES is a bad connection between the game and the NES motherboard itself. This is caused by the infamous “72 Pin Connector” that the Toaster NES has. This connector is very sensitive to dirt and dust and dirty connections will almost always be the culprit. Sometimes the 72 pin connector itself is bad due to it getting bent or broken but this is more rare and a good cleaning should at least be tried to restore it back to original functionality.

I hate the Nintendo NES 72 pin connector from the Toaster!
I hate the Nintendo NES 72 pin connector from the Toaster!

Once you take apart the NES you need to slide off the 72 pin connector. Just wiggle it back and forth until it slides off.

Pulling the 72 pin connector off the Nintendo NES motherboard
Pulling the 72 pin connector off the Nintendo NES motherboard

With the 72 pin connector off the NES motherboard you can now clean the pins with a 50/50 mix of alcohol. I’ve always had good luck with the 50/50 alcohol but there are other ways you can do it. I dipped Qtips in alcohol and then scrubbed off the pins on the motherboard. Using the other end of the Qtip or a clean rag wipe off the contacts until they are clean and dry. As you scrub the contracts your Qtip will turn black. The black is all the dirt and crud accumulated of the 25 plus years the NES has been around.

Now that the NES motherboard is clean you can turn your attention to the actual 72 pin adapter. Over time it gets worn out and dirty so the first thing you want to do is clean it off using the same 50/50 alcohol.

The infamous Nintendo NES 72 pin connector in all it's glory!
The infamous Nintendo NES 72 pin connector in all it's glory!

Take a Qtip and dip it in the alcohol and run it over both rows of pins on the 72 pin connector. Use the other dry end of the Qtip to scrub the rows clean and dry. Just like when you clean the NES motherboard your Qtip will turn black.

Since the toaster NES has you put in the games and then press the game down into place, this bends the pins on the connector over time. They get stuck bent down and it give you little or no connection from the game to the motherboard. To fix this you can use a dental pick or a very small flat blade screw driver to bend these pins back up into place.

How a Nintendo NES game cartridge looks in the 72 pin connector
How a Nintendo NES game cartridge looks in the 72 pin connector

57 thoughts on “How to troubleshoot, diagnose and repair Nintendo NES common problems”

  1. Thanks so much for the tips! I was able to get my NES working again after taking it apart and cleaning the 72 pin connector.

  2. If they hadn’t all been stolen, I’d be taking apart my old Nintendo systems right now. Not even sure how I stumbled across this. You did a good job with the pics, and explaining not only the steps, but what YOU did to complete them. And I didn’t get the feeling your were talking down to me.
    One suggestion. If you could circle or highlight the correct chip for the people who don’t know what a microchip looks like. I’m pretty sure I can see where the pin is missing in the 2nd photo; and if I’m not positive, there are plenty of people who won’t have a clue.

  3. i read everything on here cause i had a problem with that chip you said. my sistem and games run so much better. you genious thank you so much πŸ™‚

  4. I have the red flashing light problem in one unit and the other unit has a solid gray screen. Cleaning and bending pins had no effect. Do you think I am not being aggressive enough with the pins or something?

    1. For the NES unit that has the red flashing light problem: Make sure you clean the NES motherboard pins where the 72 pin connector installs onto. If it’s dirty it causes a poor connection and will cause your NES to reboot over and over. It’s not reading the game so the lockout chip (called 10NES) causes the NES to reboot over and over in 1 second intervals.

      To troubleshoot the NES with the sold gray screen I would first make sure the game you’re testing it off of is clean and will work in another NES. Sometimes you need to “wiggle” the game after you press it down into the NES. The far left and right pins are the most picky.

      I’m assuming you cleaned and tried to align the “front” par of the 72 pin connector where the games get inserted into.

      Look at the back of the 72 pin connector and see if any of the pins are bent or sticking out. It should look uniform all the way across or else you have a problem. Sometimes especially with the far left and right end connectors they can get bent and will not make a firm connection.

      If all this does not work your 72 pin connector will most likely need to be replaced.

  5. I repositioned the 72PC pins and games turn on but are pixelated and have lines and wrong colors. The mother board is dusty should I clean every bit of time and rust next? Thnx for your consideration

    1. You may have dust or debris in the 72 pin connector so I would definitely make sure it’s completely clean. Since you “repositioned it” I suggest you inspect it for bent pins as this type of a problem can give you strange graphic glitches especially if you are trying to play games that you have already cleaned thoroughly.

  6. I replaced my 72 pin connector, cleaned the system inside and out and tested all my games on my old top loader to make sure they worked. Yet, after replacing and cleaning my old toaster model the screen either loads a solid color or very pixelated graphics and then freezes after a few seconds. Like I said, my games are cleaned and load fine on the top loader. Do you have any idea what might be wrong?

      1. Yes. It will either be one solid color or the game will come on but the graphics are completely distorted.

        1. I would check the new 72 pin connector and make sure none of the pins are bent or out of alignment. You should also try cleaning it with alcohol just in case it’s dirty. If all of that fails try using another 72 pin connector. If you get the same result with that I have seen where bad video ram can cause the issue you are talking about. If that’s the case you would have to desolder it and replace it.

          1. I was able to get it working by removing the 72 pin connector and cleaning the metal pins on the motherboard it attaches to. The pins were caked pretty hard in green residue, but I took some lime away and a toothbrush to the board and cleaned it off. The nes now works again like it did in the 90s. It doesn’t play a clean game right away, I still have to blow in the cart a bit to get it to work, but after that they turn on and run just fine.

  7. Thanks for the info – I was able to get my NES Working again. I used an eraser to clean the connector on the motherboard, which seemed to work pretty well. I also read some “Weiman Glass & Stove Top Cleaner” works well, but didn’t try that. I did find I had to give the NES a Smack or two when playing certain games for whatever reason.

  8. Hi Steve, I recently broke out my old NES from the deep, dark recesses of my closet and tried to fire up my games. I initially had the blinking red light of death, but was finally able to get it to load my games with at little compressed air blown into the 72 Pin connector & the game contacts. Unfortunately, I can’t choose between 1 & 2 player modes (or between saved games) on the title screen. I took the unit apart and cleaned all the dirt & cobwebs off of the mother board. I also removed the 72 pin connector and cleaned it the best I could – I did notice a couple of bent pins along the back side and tried to bend them back as much as I could. I’ve tried switching controllers, but no success. The directional buttons on the controllers work just fine while playing the game, just not on the title screen… any suggestions?

  9. This is a great guide. Many problems have came from that terrible 72 pin connector. I remember there was a time back in the early 2000s that if you emailed or called nintendo usa they would actually send out one replacement part. Ironically i had ordered one for another console of ebay and compared to the nintendo replacement the aftermarket was much more reliable.

  10. Hi, I’m stuck in this problem: I can hear audio of the games, but only have a blank screen. I’ve already tried to brush and clean the 72 pin connection to the cartridge and the connection to the motherboard. Any suggestion?
    Thanks for the useful guide!


    1. Marco – Are you using RCA audio/video cables or an RF adapter? Also which model NES are you using, the Top Loader or the Front Loader?

  11. Hello. Question for you. I just recently pulled out the 72 pin connector and raised all the pins up and cleaned them with rubbing alcohol as I was having game freezing issues. Since the cleaning it seemed better but the games still freeze and I get colors that change on the screen. Any ideas as to what else could be wrong? I have cleaned the games connector with alcohol as well so they should be clean. Not sure what is causing the freezing.

    1. Forgot to mention that I am not using the original Nes ac adaptor as I didnt have it, voltage is the sames, amps are off slightly. I have ordered a replacement. I get a hum which I assume is the wrong ac adaptor, not sure if this would impact the game freeze issue. Thanks

      1. I have seen aftermarket AC adapters cause issues so please let me know if that fixes the “humming” or the intermittent freezing issue.

  12. Rather unique problem. The game loads, no blinking light, but the main character or potion that would be controlled by the controller is not reading. Mario doesn’t appear in Mario games, Simon isn’t on the screen for castlevania. Best that I can guess is that perhaps the mother board is corrupted? Has any one else had this issue and can it be repaired? We have tried multiple controllers and games and it the same issue.

    1. This could be caused by bad RAM or potentially the PPU itself. To replace the RAM or PPU would require de-soldering them from the NES motherboard which depending on your tools and skill set can be challenging.

  13. I’ve cleaned the games, motherboard, 72 pin connector and the system only sporadically works. The only game I can consistently get to work is Tyson’s Punch Out. Even then I have to push the cartridge in harder then normal. Suggestions?

    1. Two things I can think of: It sounds like the 72 pin connector is out of alignment and or your games are very dirty. Have you opened the games to clean them? Some games are so dirty that you need to open them up to clean them properly.

  14. Steve,

    What tool do you use to get the back off of the NES to get to the mother board? I do not have a screw driver long enough with the proper head to fit the screws properly.


    1. Jay,

      It came from Nintendo with Phillips head screws. A number 1 Phillips screwdriver is all you should need but it’s possible that somebody may have swapped out the Phillips screws for something different.

  15. i have a new one for me, i have fix at least a dozen NES systems, rebent the pins, clean it up, disable the ten chip etc… never had an issue… have a system now that worked just fine, but i took it apart and painted it… put it back together… powers on fine, but as soon as i push in a game to the now tight pins, the power goes out… can’t figure out what is going on. Any ideas?

    1. Are you sure that the pins are correctly aligned in the 72 pin adapter? If not it could be bridging between two points and causing the issue. Does it happen with multiple games or just one game?

      1. i pulled the OEM pin connector, checked it, everything looked ok, but that seemed to be the source of the issue as it is the only thing in play when you add a game, i switched it out to an aftermarket pin just to check and the aftermarket one works flawlessly.. Hate using the aftermarket parts, but if it works.. so be it… .

        1. Ok I finally figured it out!!!!

          So I have two tvs in my living room. And after almost giving up. I thought. Let me try the other one. Both flat screen HDMI.. So never really occurred to me to before. turns out that one is LCD and one is LED. Apparently the nes can’t handle the aspect ratio of one of those. After switching the pin connectors, buying another nes, multiple cleanings… Finally!!!

  16. Hey, I have already fixed up two NES consoles that belonged to two of my brothers, they work flawlessly. Of course I fixed them before I found this page. My problem has arisen with my third attempt, the console was an old and dirty one that was stored in a re-purposed corn bin for storing junk. The console had corrosion, it’s door flap on the front was gone, it had a dead spider inside of it. Along with some mouse terds, and all that sort of stuff…

    So I brought it inside and I opened it up like the other two, cleaned out all of the impurities (there were a lot of those, but it is practically spotless now), and fixed the severed wires that work perfectly now. And after some tests by swapping out the pieces between the bad console, and one of the other previously restored consoles (primarily the 72 pin connector, and the motherboard), I came up with these results:

    Good board with bad connector = terrible graphics, but game events and program work.

    Bad board with good connector = not as terrible graphics, but game events and program work.

    I boiled the 72 pin connector to super clean it (the steam smelt terrible, but that means that it worked), and I bent the pins back into place (the ones in the back drove me crazy like always, but these were different, as two of them were bent up too much, but I managed to fix them). And I put the connector back in the console, and it had the same not-as-terrible graphics that came with the bad board but good connector. So now the 72 pin connector is not the problem.

    But again, the graphics looked like weirdly colored squares (but the game program still works). So the problem is with the board (I know that it is not with anything with the box itself, as I swapped out that too, and that had no result, so it’s good). I have a suspicion that the problem is either small amounts of corrosion on the connector thingy on the board that attaches to the 72 pin connector (but I used some REALLY strong stuff on it, so I don’t think it is the problem, but it might be), or something about that little metal box that connects to the power source, and the television. I do know that the problem shouldn’t have anything to do with the actual board itself, as there is no evidence of corrosion on the green board itself (other than the connector connection thingy).

    The corrosion (very small amount, but that could have big effects) on the board is rather finicky, any ideas of how to completely remove it without damaging the board (I.E. I can’t boil it away like the 72 pin connector, as it would literally take forever to dry it, plus, it is just dumb)?

    But if the problem is with the little metal box (as the box has quite a bit of corrosion on the outside, so I suspect it has some inside as well), do you know how to open it up to see what the problem is? I tried somethings, but they never seemed to work in opening it, plus, I really don’t want to break it, as I want to sell the NES when I’m done. If I can figure out how to open it, then I can open it up, along with that of the good console, and compare them to see what important differences there may be.

    So between these two alternatives, corrosion and that metal box, which one is more likely to be the problem (I’ll look into both), and how would I go about solving either of them?

    1. Unfortunately both of them could be contributing to the problems you’re describing. The little metal box has the RF and power supply circuitry built into it. There’s a lot of capacitors and other components in there that could cause you issues. To open it you would need to desolder the tabs that closes the unit together. If you want to attempt to fix the motherboard that is missing traces you could run “jumper” cables from a good trace over the parts of the trace that are missing to effectively bypass the damaged parts.

      1. After like 2 months πŸ˜› I have learned a lot about the mechanics of this thing…

        With some research revolving around a very buggy DVD player, I am convinced that the problem is a bad capacitor (I haven’t had time to check them yet unfortunately). Thanks for the help, if I run into any other problems, I will come back here and ask πŸ˜€

  17. Thanks so much for these tips! I was able to fix my childhood NES!

  18. Thankyou for the helpful article..would the light blink of an on without a game inside…iam pretty sure the 72 pin is bent..but just wondering about the light flashing before I put a game in

  19. Hey Steve, Thank you very much for this nice and precise tutorial. I bought three NES in Salvation army some years ago and decided to mend them. Two of them would give me a blinking screen when i tried to load a game. They came back to life after isopropylic alccol cleaning, cleaning might not be perfect since i have to load the game two or three times before it works but i played Zelda which is already a great success!

    The third one though won’t turn on at all. I assume the power supply is not in cause since it works fine with the two others. I mesured the tension outside the big capacitor out of the metal box and i get a very weak signal.

    Do you think it’s worth unsolder and opening the metal box to check if a capacitor would be “burnt” somehow? Is it noticeable with a naked eye?

    What other factor would cause that kind of symptom? (Not turning on at all)

    1. Yes, it’s definitely worth opening it up and checking it out. Look for cracked solder joints or leaking capacitors. You may even find scorched components. The only way to know for sure is to open it up.

  20. My nes powers on but I can’t get anything on my TV thru the av cables the TV says not connected and to check the connection could I buy a new av/rf power module for it or do I have to change out the caps or is there anything else I should try first

  21. Followed a few different blogs and cleaned both the pin connector, the board and games

    I had a few issues initially so went back and re-cleaned everything and put everything back

    Now I’m having issues with alignment. The only way I can get a game to work is by pushing and holding down the cartridge upon the first push down ( insert cart, push down all the way and hold). Turn power on and will work 99% of the time

    Can’t seem to fix the alignment. Any tips ??

    1. It sounds like the pin connector pins may be bent too far out which is why you need to hold the game down. If you don’t want to replace the connector you will have to bend them back.

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