Famicom with AV Mod is not working

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lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: Famicom with AV Mod is not working

Post by lidnariq »

Yes, 10k from CPU /RESET (pin 3) to +5V (pin 40). See if the voltage does rise, and if it does rise, if pin 4 starts changing.
Mitchel
Posts: 11
Joined: Mon Feb 06, 2023 12:45 am

Re: Famicom with AV Mod is not working

Post by Mitchel »

lidnariq wrote: Wed Feb 08, 2023 12:03 am Yes, 10k from CPU /RESET (pin 3) to +5V (pin 40). See if the voltage does rise, and if it does rise, if pin 4 starts changing.
Pin 3 now has a voltage of +2,63V and pin 4 now has a voltage of +1,57V.
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: Famicom with AV Mod is not working

Post by lidnariq »

But pin 4 doesn't continue to change?
Mitchel
Posts: 11
Joined: Mon Feb 06, 2023 12:45 am

Re: Famicom with AV Mod is not working

Post by Mitchel »

Sorry for just getting back to you, but I have limited access to an oscilloscope. With the pull-up at the reset pin I get a signal at pin4 which has a level of +3V. I could test this now. Afterwards with full euphoria I soldered the AV Mod back on and plugged in a game. After switching on I could see the game for a short time, but then more and more artifacts appeared until the game froze. Since then I can turn on the console, but I can't see the game anymore.

When I have the game plugged in, there is no data signal on pin4. Sometimes the signal is High, but most of the time it is Low. But without the game there is a data signal.

I hope that I have not destroyed the game.

Do you have more tips what I can test?
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: Famicom with AV Mod is not working

Post by lidnariq »

I think you might have cooked your CPU when you soldered to the audio pins...

What's supposed to happen is:
* if pin 3 is high
* and pin 29 is receiving a clock
* then pin 31 will emit a clock that is 1/12 (or 1/15 or 1/16 for other regions) of pin 29
* and pin 4 will continue to toggle low/high no less often than every 5 counts of pin 31 until the CPU receives an instruction that causes it to crash. (Design flaw in the 6502)
Mitchel
Posts: 11
Joined: Mon Feb 06, 2023 12:45 am

Re: Famicom with AV Mod is not working

Post by Mitchel »

lidnariq wrote: Fri Feb 10, 2023 6:35 pm I think you might have cooked your CPU when you soldered to the audio pins...

What's supposed to happen is:
* if pin 3 is high
* and pin 29 is receiving a clock
* then pin 31 will emit a clock that is 1/12 (or 1/15 or 1/16 for other regions) of pin 29
* and pin 4 will continue to toggle low/high no less often than every 5 counts of pin 31 until the CPU receives an instruction that causes it to crash. (Design flaw in the 6502)
I guess that doesn't sound good to me, unfortunately. Is there still hope for the Famicom board or does it look very bad now. The screen is black/green when I turn it on, just like before. Nothing has changed.
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: Famicom with AV Mod is not working

Post by lidnariq »

I suspect you only damaged the CPU, so it's probably repairable... but maybe not for cheaper than another original RF Famicom.
calima
Posts: 1745
Joined: Tue Oct 06, 2015 10:16 am

Re: Famicom with AV Mod is not working

Post by calima »

Are the clone CPUs on Aliexpress more expensive now?
Mitchel
Posts: 11
Joined: Mon Feb 06, 2023 12:45 am

Re: Famicom with AV Mod is not working

Post by Mitchel »

Ok that's a pity. Nevertheless, thank you lidnariq for your support and your help. Then I will probably have to look around for another.
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: Famicom with AV Mod is not working

Post by lidnariq »

calima wrote: Mon Feb 13, 2023 12:06 am Are the clone CPUs on Aliexpress more expensive now?
Yes, and also good luck actually getting an NTSC one with the ÷12 prescaler and not a remarked PAL one with a ÷15 or ÷16 prescaler.
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