Famicom sound problems only with spesific sounds

I have AV-modded couple original Famicoms withour any issues, but now I have one.



This one console works otherwise but some spesific sound effects sound wrong and only in sone spesific games, issues are not present in all games. In that recording Mega Man 3 is fine, but in Castlevania item pick up sounds wrong. Same issue is with all Castlevania games, also in Contra the gun sound is not what it is supposed to be. All three Super Mario Bros games are fine.

For testing I have tried soldering audio wire directly to pin 1 of cpu which seems to produce those effects and they sound wrong from that point also so is the cpu defective?

 

Did you try soldering the audio line to pin 46 of the cartridge slot? That's where expansion audio is mixed in with mono audio. Pin 1 of the CPU only contains half of the sounds. The other half is on pin 2. These signals are combined into mono audio later in the audio circuit.

 

Yes, I did solder to pin 46 of cartridge slot at first (and it currently is soldered to that pin), that cpu pin 1 was just for testing and the problematic effects seem to originate from tha pin, apparently it contains the problematic channel.

I have another modded machine, same motherboard version if I remember correctly. It is modded using the same instructions and it has worked fine several months.

 

Hmm then maybe there is something wrong with the CPU. Hopefully someone more knowledgeable about this than me can help.

 

This issue is indeed very strange, I would imagine that Mega Man and Super Mario Bros games all use that same channel for same purposes and if so, strange that those sound effects work just fine. What do Castlevania and Contra for example do differently? I forgot to mention that Battletoads is also suffering same issues, some spesific effects are just wrong.

 

Not sure if this article will help but it has the pinout of the CPU and explains what each signal is: http://wiki.nesdev.com/w/index.php/CPU_pin_out_and_signal_description

Pin 1 is the output for both pulse waves so maybe one of them isn't generating or isn't working right?

 

something is wrong with the processor, i had a junk famicom that had sound distortion on some of the channels, wierd tingy noises instead of the regular stuff we're used to, it was the damn CPU. they can be had cheap on Aliexpress etc.

 

I happened to search aliexpress earlier, did you order replacement there and it worked just fine?

Edit: well I just went ahead and bought one, hopefully it works.

 

just make sure it's an NTSC cpu and you'll be fine, i ripped the one i had out of another parts famicom. they should work fine since they are ACTUAL cpu's not clone blob top SOAC. and the project famicom boards on ali have them and everything sounds 100% on those, Akumajo Densetsu etc. all work perfectly

 

All this talk about Famicoms makes me wanna go play mine. It also reminds me that I need to install the HDMI mod or the NESRGB board.

Hopefully this new chip fixes it.

 

I think RP2a03e is always NTSC and PAL version had bit different model number?

 

you are correct. some sellers have them listed as NES cpu not the actual part number. so thats why i mentioned the NTSC /PAL thing

 

PAL CPU is RP2A07.

letter after the number is chip version.