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AC power problem

Discussion in 'Troubleshooting and Repair' started by stevew, Oct 11, 2012.

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  1. stevew

    stevew

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    Jun 16, 2012
    The NES game system comes with a 9V AC power adapter. My system started getting a ton of wavy lines across the screen recently. I read that the NES will also function with a 9V DC power supply. I tried a 9V DC power adapter from another device and the wavy lines are gone.

    I also tried NES AC power supplies from other NES systems and they all make wavy lines appear on my system. So I assume that when using a DC power supply I am bypassing the AC to DC conversion inside the NES and that is where the problem is.

    I could just purchase a DC power supply for my NES but I'd rather just fix the problem, it's probably cheaper to fix it anyway.

    Does anyone have any guesses as to which component is likely the culprit? I assume that the conversion would happen closest to where I plug the power adapter into the system. A rectifier circuit of some sort... I don't see any obvious problems, the capacitors do not appear to be leaking or swollen...

    Thanks,
    Steve
     
  2. Jotto

    Jotto

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    Aug 24, 2012
    Sounds like a filtering problem, look at your capacitors. Don't rely on them always being domed at the top, or blown up. Capacitors start going bad when they are made.
     
  3. twbranch

    twbranch

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    Oct 10, 2012
    Ditto, Jotto
     
  4. stevew

    stevew

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    Jun 16, 2012
    NES

    There is one large capacitor in that circuit, a 2200uf, I'll try replacing that, thanks
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Could you describe the wavy lines in more detail?
    Is there anything you've changed or added recently?
    Did the problem appear suddenly or has it been gradually getting worse?
    What is the screen? Is it part of the game, or an external monitor? Does it work OK displaying any other signal from any other device?
     
  6. stevew

    stevew

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    Jun 16, 2012
    The wavy lines are just everywhere... everything that isn't black I see a wavy darker line in it like ~ well, maybe more of a curve. The games play fine though.

    Nothing changed, I didn't use the system for a few months and now I turn it on and the lines are there. It happens on all my TVs, I tried it on LCD TV and DLP. It also happens no matter which way I hook it up, composite or RF... and the lines only appear when the normal NES 9V AC adapters are used, a DC adapter I have causes no lines. Also if I use the same AC adapters on another NES I don't see any wavy lines.

    I had to order a replacement capacitor (2200uf) but haven't received it yet. I'll let you know if that works.

    Thanks
     
  7. stevew

    stevew

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    Jun 16, 2012
    fix

    The large capacitor didn't fix the problem, I think there are a few more but I have to unsolder a shield to get to them.

    I've attached a picture of the lines, it is actually a lot worse than this but when I take the picture half of the lines don't show up...
     

    Attached Files:

  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Can you find a schematic diagram of the NES?

    I tried googling it, but the closest I can find is http://nesdev.com/Ntd_8bit.jpg which doesn't include the power supply section, and may not even be for the NES - the title includes "NTD". I might have some suggestions if I could see a schematic, but not without one.
     
  9. duke37

    duke37

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    769
    Jan 9, 2011
    That looks like radio frequency patterning on a TV.

    This could perhaps be due to the switch mode power supply not being smoothed properly on its output or the system not filtering out a ripple on the input.
     
  10. stevew

    stevew

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    Jun 16, 2012
  11. Raven Luni

    Raven Luni

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    Oct 15, 2011
    Thats depressing:(
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Thanks for finding the schematic. Well, the power supply circuitry is very conventional. It should behave OK with DC or mains-frequency AC input.

    I notice that the video circuitry is next to the power supply on the schematic. That doesn't mean they're close by on the circuit board though.

    I guess it's possible that the 7805 regulator is oscillating when its input voltage is higher (9V AC from a transformer will produce significantly more DC input voltage to the 7805 than 9V DC from a regulated power supply).

    I would first replace the capacitors closest to the regulator - there are three 0.01 uF caps, a 10 uF cap and a 100 uF cap. If that doesn't help, you could try replacing the 7805 regulator itself.

    Another experiment that could tell us something useful is to connect just the ground connection from the NES to the TV/monitor (but not the video signal) and see whether the patterning appears on top of the picture. Tune the TV in to a channel, or provide video from another source, and touch the outer connection of the video cable from the NES onto the outer connection of the TV's video input connector. If any interference appears, the NES is producing "common-mode" interference. Given your description, I don't think that's the case, but you could check.
     
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