SNES Mini/Jr won't power on

hernan43hernan43
in Help Wanted!
So I have a pristine _looking_ Super Nintendo "Jr" that does not power on. The previous owner appears to of spilled cola of some kind in it. 



Opening it up the motherboard also looks pristine with a few sticky spots that I've since cleaned.



Using my multimeter I can see that the power jack works and provides 9.3V. The fuse is also fine. The choke appears to be fine as well. The problem is that the voltage regulator does not recieve power on the input leg. Checking the input and output on the 7805 both give a value of 0.000V. Checking the power switcvh with the continuity meter shows that the switch is working.



I've tried 3 different 7805s before realizing that if the input leg isn't getting power the 7805 isn't going to do anything. 



So I am wondering what other components to check? I feel like I've checked everything under the sun. Anyone have any ideas?



--Ray

Comments

  • PikkonPikkon
    For the input side do you check to see if there's any continuity.



    I made this for another member here,just traced out the 7805.

    https://imgur.com/dJGPsY7
  • hernan43hernan43
    Thanks so much for that pic. I have continuity between both of the point shown in the image. The motherboard really is pristine in appearance I don't see any damage to it anywhere.



    I've been trying every test I can think of. It is hard to follow the traces since they seem to be well concealed under the solder resist. Thanks again for the pic that was very helpful.
  • PikkonPikkon
    No problem but I would check out the caps that lead to the 7805,might have some bad ones.
  • MobiusstriptechMobiusstriptech
    This will sound dumb, but did you check the power switch and the voltage coming in from the ac adapter?
  • retroupgraderetroupgrade
    The last time my SNES jr died, it was because of an old 1st party ac adapter that drifted into higher voltages. The 7805 and fuse died very gradually. Troubleshooting took a while.
  • hernan43hernan43
    Is there a sure fire way to check if cap are bad using only a multimeter? Or do I need a capacitor checker thing? My multimeter has an ohmmeter but not a capactiance meter.



    --Ray
  • MobiusstriptechMobiusstriptech
    No. You need to be able to test ESR and capacitance.
  • hernan43hernan43
    Yeah that is what I was afraid of. I might just replace the caps anyway. Trying to find a legible schematic online so I can try tracing the issue.
  • MobiusstriptechMobiusstriptech
    There are schematics on the Console5 wiki pages.
  • hernan43hernan43
    Yeah I just found them right before I saw this. They have one giant one in the lot which looks pretty comprehensive. Thanks!



  • MobiusstriptechMobiusstriptech
    Yep. It's a good schematic. I have used it to diagnose issues in the past.
  • PikkonPikkon
    Didn't catch the part that the output is not working on the 7805,if that's the case your problem should be before the output.

    As for the switch you can always jump it to rule it out.



    If anything post some pics of your board.
  • hernan43hernan43
    Ok so I recapped the whole mamma jamma and replaced the choke and the 7805. I still had no power coming into the 7805.



    I ended up taking another look at the power switch( with the corroded leg). Turns out the pads on the underside were fine, but the pad on the top of the mother board for one of the legs was gone and i think most of the via was gone as well. So I rubbed off a bit of the solder mask and soldered a wire to the corroded leg and the other end to the ad hoc pad I just made. Boom, the SNES now powers on and displays a picture on the screen.



    Unfortunately the picture is totally garbled with every single game. It doesn't matter how much I clean the cart or the connector. The game *plays* fine and the audio is fine, but the graphics are just a jumble of tiles and letters.



    Searching around it sounds like it could be the PPU or the RAM for the PPU. Does anyone here have any experience with this? Is there a way to tell if it is the PPU or just the RAM for the PPU?
  • PikkonPikkon
    On a snes jr the cpu and ppu's are combined into one chip and that's not something you can buy,would have to be sourced from another snes jr.



    If your handy with a soldering iron you can reflow all of the ic chips and look for any broken traces.
  • hernan43hernan43
    Ok so I rewetted all the joints of all the chips. I did see somewhere that this can sometimes be caused by the sram chips so I did replace those. The console seems to work fine but still has the garbled graphics.



    I'm guessing something must be gakked up with the CPU. I'll probably just stick this on the shelf on the off chance I come across a totally destroyed jr with a "good" CPU.



    Thanks to everyone for the help. This was a fun exercise even though the outcome wasn't what I wanted.
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