SMB1 Working but not SMB3

Discuss technical or other issues relating to programming the Nintendo Entertainment System, Famicom, or compatible systems.

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trobby420
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SMB1 Working but not SMB3

Post by trobby420 »

I have purchased an populated the NESessity v1.3 Replacement PCB for NES Console. It seems only a couple games work tho.

I am having this really off issue where I can only play my older games (ie. Super mario bros and Milton’s Secret Castle). super Mario Bros 3 just freezes and stutters at the top of the curtains. I have replaced the CPU, PPU and Clock. I am so stumped.
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Ben Boldt
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Re: SMB1 Working but not SMB3

Post by Ben Boldt »

The only things I can think of:

- Dirty connector/games
- problem with /IRQ signal. The older games might not enable IRQ. This signal may need a pull-up resistor or something.
trobby420
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Re: SMB1 Working but not SMB3

Post by trobby420 »

Ben Boldt wrote: Fri Jan 14, 2022 12:03 am The only things I can think of:

- Dirty connector/games
- problem with /IRQ signal. The older games might not enable IRQ. This signal may need a pull-up resistor or something.

It’s not the dirty connector or games because I have been using the same ones between a original hardware and the rebuild
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Dwedit
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Re: SMB1 Working but not SMB3

Post by Dwedit »

Maybe check for continuity between the CPU IRQ pin and the cartridge slot's IRQ pin?
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Ben Boldt
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Re: SMB1 Working but not SMB3

Post by Ben Boldt »

Also, I believe /IRQ should be always high when you turn on the NES with no cartridge inserted, or when running SMB1. If you don’t see 5V, you may be missing a resistor from /IRQ to 5V, or may have the incorrect resistor, etc.

You can safely add a 10k resistor from /IRQ to 5V at the cartridge connector as an experiment. If the experiment fixed it, you should still locate the original resistor and figure out why it isn’t working.
trobby420
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Re: SMB1 Working but not SMB3

Post by trobby420 »

Ben Boldt wrote: Fri Jan 14, 2022 8:05 am Also, I believe /IRQ should be always high when you turn on the NES with no cartridge inserted, or when running SMB1. If you don’t see 5V, you may be missing a resistor from /IRQ to 5V, or may have the incorrect resistor, etc.

You can safely add a 10k resistor from /IRQ to 5V at the cartridge connector as an experiment. If the experiment fixed it, you should still locate the original resistor and figure out why it isn’t working.


Thank you so much. Turns out the my resistor array was in backwards from the beginning and was not getting the proper resistance as you stated above. Thanks again!
trobby420
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Re: SMB1 Working but not SMB3

Post by trobby420 »

Dwedit wrote: Fri Jan 14, 2022 7:40 am Maybe check for continuity between the CPU IRQ pin and the cartridge slot's IRQ pin?
Thanks for the answer it definitely helped me get to the solution.
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Ben Boldt
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Re: SMB1 Working but not SMB3

Post by Ben Boldt »

Cool, thanks for letting us know how you fixed it.
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