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NES connector replacement and disable lockout IC to correct blinking light problems.


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  • NES connector replacement and disable lockout IC to correct blinking light problems.

    Hi all,

    I bought an original NES (Mattel version) with a few games a while back which was working but games would not always load even after cleaning edge connectors, a typical issue.

    The main problem of course was the troublesome 72 pin connector which in this case may have been badly 'readjusted'. The games were more likely to work if not latched down and for that matter the latching mechanism wasn't working anyway.

    A lot of the time the games which would not load were triggering the 'blinking light' fail despite the fact that they were genuine, format and region correct games - why?

    The answers to all these issues were available in various posts online but I never saw a straightforward one which addressed all these issues together.

    So at the risk of repeating common knowledge, here's a basic summary

    The lockout chip, sometimes referred to as 10NES (it is u10 on my NES's PCB) communicates with a corresponding chip which must be present in every game cartridge. I believe this means that codes are sent and received, via some of the edge connector contacts purely to establish if a cartridge is genuine and region correct.

    If anything is wrong with the interaction, from the IC missing or incorrect region to simple problems with connectivity the lockout IC sends a hardware reset to the CPU. Repeatedly, hence the 'blinking light'.

    In a perfect world that would be fine, providing your carts were genuine but having engineered a less than perfect method of connecting the cartridges Nintendo created an issue which would plague all owners of genuine NES games as well as their intended 'pirate' adversaries.

    Near the end of NES production, around the time of SNES release Nintendo created a cost-cut version of the NES to extend its sales life, the now prized 'top loader'. Prized perhaps as it is less common but mainly as it is less troublesome, Nintendo having given up on the front loading 'toaster' mechanism and critically, omitting the lockout chip altogether.

    Given that, the obvious cure for the common non-loading and 'blinking light' problems is to replace the 72 pin connector, as aftermarket replacements are readily available and while you're at it, disable the lockout IC. It turns out this is not difficult as the reset signal is sent from pin 4 of the IC and cutting this pin prevents that occurring.

    I understand the purists who do not like to modify their machines or possibly enjoy staring at a flashing red LED! In my case, given that Nintendo left it out of the top loader altogether I don't have a problem with it, consider it an upgrade...

    And the non-latching problem was caused by previous incorrect assembly of the cartridge guide, a little flange must hook under the PCB as it is installed, not sit on top.

    All the photos and procedure for replacing the 72 pin connector are included on my updated NES page

    Hope this helps someone, sometime - Regards, John
    more from John's Retro Workshop -

  • #2
    Cleaning the connector works only if you removed the connector from the board, otherwise you are only really cleaning one side of the swipes. I have removed 3 in the last month and cleaned them this way and all 3 were restored. Cheers.


    • #3
      Good advice, Thanks!

      - actually I meant cleaning the card edge on the games didn't work.

      I didn't really try to save the old connector in this instance, it was apparent that someone had already been at it and bent the contacts.

      Best regards, John
      more from John's Retro Workshop -


      • #4
        Thanks jbtech- you've just saved me and probably a heap of others a lot of research time into this issue!


        • #5
          Thank you - I must acknowledge wyldcat34 is right - in many less extreme cases removing and carefully cleaning the 72 pin connector and PCB edge contacts could get it working.

          All the best, Regards John
          more from John's Retro Workshop -


          • #6
            Ouch! bent pins! Sorry I mis-read. Sometimes cleaning the edge pins is all it needs, but mostly not now - all that blowing in them before loading them may have worked at the time
            This is still my favourite Game skit!


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