Broken Famicom - garbled graphics/crash after few mins of play

[toadhall]

Hi all! My Famicom decided to suddenly crap out while playing recently.

When I boot up a game after having not booted the Famicom in a while, it will let me play the game for a few minutes. Then it will flash random garbled graphics on screen, and then crash:



Notice the minor glitch in the "9" at the top, the white splotch at the bottom, and the random 1ups that shouldn't be there.

And then if I try powering off and on again, it will give this delightful mess:



Sometimes, instead of a garbled screen, it will just give me a blank yellow screen and play a random sound effect (like getting a coin in SMB).

Any clue to what this is a symptom of? Broken PPU? Messed up SRAM? If it helps, this Famicom recently had an AV mod done on it but it was working fine for a while after that.

[P]

Although the pictures show SMB I guess this happens with all games you try?
Since it has sound errors and crashes I'd guess it's a program or CPU error rather than a graphical or PPU one.
I can't say what to do except the usual advice I always give when something weird happens though.

Clean cartridge and cartridge connector pins.
Test AC adapter with a multimeter or try with another one with the correct specs.
Do continuity tests on traces.
Maybe try replacing the electrolytic capacitors.

[toadhall]

Yeah, it happens with other games as well. I just used SMB as my example as that's my favourite game to showcase when something goes horribly wrong. The first time this actually happened was while I was playing my copy of rom-swapped Lagrange Point and thought something was wrong with that cart.

Is there a possibility that the CPU is borked?

I'll have to try out your suggestions next weekend. It's possible something might have fallen into the cart slot. It's certainly happened before. Thanks!

[P]

I see.
I'm no engineer but my layman guess is that it's some kind of CPU related problem, which doesn't rule out a broken CPU (I don't know how to test that though except switching it out for a known working one which is a lot of work). Broken CPUs and PPUs doesn't seem to be that common though, so I'd rule out more common problems first.

[Pikkon]

Check and see if any of the main chips gets hot to the touch.

[toadhall]

Haven't had the time to mess around with my broken Famicom just yet but how hot is hot?

"ARGHHH my fingers!!!" hot, or "Hmmm, that IS kinda hot" hot? 

[toadhall]

In the spirit of my recently resuscitated Famicom, I shall revive this thread from more than a year ago!

An update to what happened to my Famicom:

So since I last posted, I barely did anything with it because the thought of replacing the CPU just made me go meh and other efforts into diagnosing where the problem was went nowhere so I shelved the project. Now that it's been more than a year, I decided to take it off the shelf again and attempt to just replace the bloody CPU since I do have another Famicom in various states of disrepair just lying around. It does have a working CPU so I figured now would be a good time to salvage it and plop it into this other not-working Famicom.

But before I did so, I figured it wouldn't hurt to test it out first so I powered it on. Lo and behold, the damn thing works fine now??? I've tested various games, all seem to work. I also left SMB on looping at the title demo for several hours now and so far no problems... *crossing fingers*

Not even going to question why. I'm just happy it works as it should. What a strange adventure this has been!!!

[famiac]

Lol. It looked like a ram/ppu problem to me.

[P]

I don't get how a PPU or RAM problem could result in the system consistently crashing though?

When I said CPU-related problem I didn't mean that the CPU chip must be at fault, but any components that can get in the way of the CPU's work might be broken I thought. Unless the CPU is really hot to touch I'd first try to replace capacitors and such things that usually go bad first.

This time it looks like resting was doing it, but it's an old system so we never know if it will start failing again, hopefully not though.

[famiac]

Ah i missed the part about the crashing. I thought it was just the graphics getting garbled

[ericj]

Sounds like a cold solder joint somewhere that acts up when it gets warm or a failing capacitor somewhere.

[famiac]

Yeah you're right. A real ram/ppu problem would not be intermittent or sudden, it would be constant

[krzy]

Check if the 7805 stabilisator does not become too hot after those few minutes since bootup (or the heatsing does not become loose).