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PostPosted: Wed Apr 24, 2019 5:04 am 
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Joined: Sun Jun 12, 2011 12:06 pm
Posts: 541
Location: Poland
I was experimenting one day with replacing regular 7805 with a step-down one based on LM2596. Unfortunately, I forgot to solder one leg of the output capacitor. As a result (this is just my suspicion) - output voltage has risen very quickly over 5V before the feedback loop of this chip could react and it burned my PPU.
Since that time I am sceptic to non-linear regulators, especially that when I soldered the cap correctly and replaced PPU, i found out a little horizontal bars in the video which were not present when I replaced it with 7805 - probably the 100kHz switching freuqency adds significant noise.


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PostPosted: Fri May 10, 2019 1:37 pm 
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Joined: Tue Mar 22, 2016 8:27 pm
Posts: 347
Location: Minnesota, USA
It turns out the level shifters I have are similar but actually different, so I am not able to replace them... Not sure where to go next with this. It would be great if I could eliminate the CPU interposer card somehow. Right now I do not know if there is something wrong with the main board or with the interposer. It seems unlikely that this is the PPU interposer but still not impossible I guess.


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PostPosted: Fri Jul 26, 2019 4:57 pm 
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Joined: Tue Mar 22, 2016 8:27 pm
Posts: 347
Location: Minnesota, USA
FINALLY I got back to this. I replaced all 5 of the level shifter ICs. It had no effect at all. When running without an HDMI cable attached, it still works fine through the composite. When attaching the HDMI cable, it still hangs with dim LED. Not sure what to try next!

I know that all of my power supply voltages are good from the FAQ, and also I plugged the same HDMI cable into my Xbox 360 to verify the HDMI cable and the TV. That was all good. The only possible things remaining that I can tell:

  • Additional logic on each interposer card (best case scenario)
  • FPGA (hopefully not because it's expensive)
  • AD9889B HDMI chip (Hopefully not because it is obsolete now, hard to find)
  • The flash chip that runs the FPGA (seems doubtful)


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PostPosted: Wed Aug 14, 2019 10:11 am 
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Joined: Tue Mar 22, 2016 8:27 pm
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Location: Minnesota, USA
My theory is that 1 of 2 things happened:

- The 5V regulator shorted itself out somehow (which is hard to explain.) This blew up the little inductor, which generated a high-voltage spike, which broke something else that I have not found yet.

or

- Something drew lots of current, which blew the little inductor, which generated a high-voltage spike, and the spike is what wiped out the 5V regulator and broke something else that I have not found yet. Whatever drew lots of current no longer does that once getting the 5V repaired (which is also hard to explain).

From what I can tell, the Hi-Def NES has no protection for bus conflicts, which theoretically should be okay, and theoretically is the same as a normal NES... These level shifters are modern though, and they may be more sensitive or drive more current or something. It seems a little far-fetched to me that this caused enough current to blow up that inductor, especially because the same cartridge that was in there doesn't break a normal NES (other than sprite artifacts) and replacing the level shifters had no effect.

Given the fact that there is a web page posted with instructions what to do if this inductor explodes, it must be a common problem. Do we have any idea the root cause of this inductor problem when it happened to everyone else?


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