NES Read Issues - Thoroughly cleaned and lockout disabled

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dragon1freak
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Joined: Thu Jul 30, 2020 2:15 pm

NES Read Issues - Thoroughly cleaned and lockout disabled

Post by dragon1freak » Thu Jul 30, 2020 2:56 pm

So I'm posting here as a bit of a last resort as I'm at a dead end with getting this console working correctly. The initial problem was the blinking power light issue, but that was solved by correcting the height of the cartridge when it's pressed down. The current issue is that the output from the console is either a frozen menu screen at varying positions on the screen, solid-colored screens, or random artifacts as shown in the linked images.

I've tried all of the usual fixes that seem to be on different guides and videos, including:
  • Cleaning all of the contacts with rubbing alcohol on both the game, the 72pin connector, and the contacts on the board for the 72pin connector
  • Bending the pins of the 72pin connector up and boiling it
  • Disabling the lockout chip
  • Visual check of all the components on the board
Cleaning everything seemed to get the best result as when initially powering on the console i got the full title screen of Golf in the correct position, but it froze up again. I clipped the pin of the lockout chip so I can bridge it to revert it if needed, but it didn't seem to make a difference. The only other thing I can think of is in the area where the power input and outputs are, a component seems to be getting very hot when it's powered on. I'm assuming the piece of metal getting hot is a heat sink and it's just doing its job, but I figured I should add it just in case.

At this point I feel like I've tried everything I could find, I can't seem to find any guides or reddit threads that list any other solutions, so any advice would be appreciated. I'm sorry if this isn't the right place or if I'm posting wrong, I had read through the newcomer post and tried to include as much info as I could, if I'm missing anything I'll try to add it as soon as I can. Thanks again.

lidnariq
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Re: NES Read Issues - Thoroughly cleaned and lockout disabled

Post by lidnariq » Thu Jul 30, 2020 3:18 pm

Crashes like what you're seeing imply only the CPU is having a problem. It's hard to say much more without better testing equipment, but it's remotely conceivable that the CPU RAM is slightly damaged.

You might check after a crash to see if CPU A0 is high, low, oscillating, or floating.

That part is the voltage regulator that converts 12-ish volts from the wall adapter to 5V for the NES and it gets rather hot during normal operation, unfortunately.

dragon1freak
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Re: NES Read Issues - Thoroughly cleaned and lockout disabled

Post by dragon1freak » Thu Jul 30, 2020 6:38 pm

lidnariq wrote:
Thu Jul 30, 2020 3:18 pm
Crashes like what you're seeing imply only the CPU is having a problem. It's hard to say much more without better testing equipment, but it's remotely conceivable that the CPU RAM is slightly damaged.

You might check after a crash to see if CPU A0 is high, low, oscillating, or floating.

That part is the voltage regulator that converts 12-ish volts from the wall adapter to 5V for the NES and it gets rather hot during normal operation, unfortunately.
I figured that getting hot was normal, but didn't want to leave anything I wasn't sure on out so thanks for confirming that.

At the risk of sounding dumb, when checking the CPU A0, is that something I can do with a voltmeter? I'm not in a rush to get it working and I'd like to be able to fix it and not just chuck it, but would the CPU having issues be something a bit more involved than a hobbyist collector should be looking into? Everything else seems to be in great condition so I wouldn't just get rid of it, but I don't really have the workspace for any sort of repair work beyond a soldering iron.

lidnariq
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Location: Seattle

Re: NES Read Issues - Thoroughly cleaned and lockout disabled

Post by lidnariq » Thu Jul 30, 2020 6:54 pm

Voltmeter should work, hopefully. If yours has a logic tester that'd be ideal, but otherwise, measure the pin Vdc relative to ground and +5V, and Vac relative to either.

If V(A0)-V(gnd) is 0V or 4V and Vac is 0V, the CPU actually crashed instead of a software infinite loop.
If V(A0)-V(gnd) is 2ish Vdc and Vac is something around 1-2V then it's a software infinite loop but dunno how.
If V(A0)-V(gnd) is 0V and V(+5V)-V(A0) is also 0V and V(+5)-V(gnd) is 5V then somehow the CPU's been told to reset even though the PPU hasn't.

I strongly suspect you'll see the first, but I'm not entirely certain how to diagnose it without either proper test equipment or another NES to swap parts with.

dragon1freak
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Joined: Thu Jul 30, 2020 2:15 pm

Re: NES Read Issues - Thoroughly cleaned and lockout disabled

Post by dragon1freak » Thu Jul 30, 2020 6:57 pm

lidnariq wrote:
Thu Jul 30, 2020 6:54 pm
Voltmeter should work, hopefully. If yours has a logic tester that'd be ideal, but otherwise, measure the pin Vdc relative to ground and +5V, and Vac relative to either.

If V(A0)-V(gnd) is 0V or 4V and Vac is 0V, the CPU actually crashed instead of a software infinite loop.
If V(A0)-V(gnd) is 2ish Vdc and Vac is something around 1-2V then it's a software infinite loop but dunno how.
If V(A0)-V(gnd) is 0V and V(+5V)-V(A0) is also 0V and V(+5)-V(gnd) is 5V then somehow the CPU's been told to reset even though the PPU hasn't.

I strongly suspect you'll see the first, but I'm not entirely certain how to diagnose it without either proper test equipment or another NES to swap parts with.
That was kind of what I was gathering from your initial reply. I'll probably keep this around to mess around with or use the case if I find a working one with a not so great case. Hopefully it can eventually be fixed but it's not the end of the world, thanks for your help!

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zoinknoise
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Re: NES Read Issues - Thoroughly cleaned and lockout disabled

Post by zoinknoise » Fri Jul 31, 2020 4:41 pm

it's possible your issue is bad SRAM inside the NES. a RAM issue can be indistinguishable from a CPU issue, and the 2A03 so far has proven to be more reliable overall than certain brands of SRAM chips. this is a problem that's beginning to pop up more and more as these consoles hit the ~35 year mark. i wouldn't say the problem is common, at least not yet, but the possibility is greater than ever at this stage.

if you have the ability, i would desolder the CPU RAM chip on the motherboard, install a socket, and replace with another 6116 chip. if you are in the US, and your NES motherboard is revision 06 or later, i can send you a tested working chip for free. (the chips i have will not fit a rev 04 or 05, or a toploader, or a Fami)

i recently tested 50 pieces of Hitachi HM6116 SRAM chips with mid-80's date codes. out of the 50, two chips failed. (and Hitachi was one of the better RAM manufacturers from this era.) that's a 4% failure rate out of a pretty small sample of 50. so the possibility you've got bad RAM in there is very real.

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