Blank screen and overheating on Famicom

[DJM]

Hi, I'd like some help identifying what needs to be replaced on my version 1 Famicom. I bought it recently and just tried booting it up. I'm running it on a PAL CRT TV and have the video signal tuned in pretty well (no static) but it's showing a completely black screen with no sound (possibly the signal not being interpreted correctly?), but blue, red and green artefacts appear when wiggling the cartridge around. I've cleaned the pins on the cartridges and the console, there's no dust or oxidation on either.

Opening it up I found that the PPU runs extremely hot, enough to burn you, and the SRAM gets pretty hot too. The CPU gets warm but doesn't seem out of the ordinary.

I bought a third-party power supply for this purpose that gives 9V. However, when testing with the multimeter, it's only getting regulated down to 7V, and that's what all the chips are receiving. I've checked all the traces and solder joints and everything looks clean and untouched.

I feel like the PPUs gotta be replaced, but what about the SRAM? And could the voltage regulator be dodgy? Or maybe just needs some fresh thermal paste? What do you guys think?

I'm a complete beginner to this kind of stuff and electronics in general so cheers for the help!

[Skawo]

I assume that the PSU outputs proper polarity (i.e negative center), right?

I'd try replacing the regulator first, since that should be outputting 5V.

That might be enough to make it work, but it's also possible that the 7V fried the PPU and/or other chips.
If the PPU still gets hot, then replace it.

The console should output something even if the VRAM is gone.

[DJM]

I assume that the PSU outputs proper polarity (i.e negative center), right?

I'd try replacing the regulator first, since that should be outputting 5V.

That might be enough to make it work, but it's also possible that the 7V fried the PPU and/or other chips.
If the PPU still gets hot, then replace it.

The console should output something even if the VRAM is gone.

Alright, sweet. I'll start with that course of action. The PSU has been tested and is correct.

Thanks for the help! I'll give updates after replacing.

[Skawo]

How'd you test the PPU?

[DJM]

How'd you test the PPU?

Sorry, typo. PSU was testing correctly. Center pin negative and outputting 9V.

[FAMICOM_87]

your PPU is fried 
one I received a NES with all chips fried , so I had to replace them all , I was lucky that I had a donor

[Skawo]

A chip running hot does not necessarily mean it's fried - you can have it running hot because of other components on the board.


That said, it _probably_ is, yeah.

[DJM]

Alright I have replaced the 7805 and it's regulating down to 5 volts again which is lovely. Unfortunately it's still not working, still getting the greyish black screen.

Did the finger test on the PPU and it doesn't actually get too hot anymore, just a little warm which seems normal considering it has a heat-spreader on it.

BUT the SRAM at U1 is getting crazy hot very quickly so I'm assuming that's dead. I read somewhere that this chip dying could prevent cartridge data from being booted which seems consistent with the issue I'm having, so maybe this could fix? Good chance the PPU is still dead though I guess.

Thanks again for the advice!