NES lacking audio

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K_Devel
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Re: NES lacking audio

Post by K_Devel » Wed Jul 30, 2014 3:48 pm

Yeah it's inside of 2v and bout 2.43v on pin 10 and the chips ground.

http://i.imgur.com/CVRqKls.jpg

Hashed out the resistors and those two transistors as far as readings go. I'm at the point of throwing this board lol.. like maybe just make a different video audio output instead, it seems so murky what's wrong here and I just can't figure it out. So close, but so far. :(

Probably a hell of a lot less complicated recreating the audio amp and going in for composite only video, could also say no to SMD :P I dunno, I'm just at my ends with it, I have like erm, 12 NES systems, and one I want to get my ACTUAL project rolling on. Would be nice to solve this one, if not for just reference for anyone who wants this ridiculously long and arduous discussion of the NES audio and how one thing leads to another, check what, fix this, all that.

Of course no matter what the result, I thank everyone who chimed in to help, that was very nice of you. Good to see people are willing to allow to help others develop a brain in this area. If everybody isn't annoyed, I'll keep trying things to get it working, and put in some sorta "final word" on all the stuff we did to wrap this up, cuz there were quite a few things replaced to even get it this far.

I was thinking, eh, just see if I can get a bunch of RF modulators on eBay, nope. Too bad handheld modders aren't just giving these out. :P

lidnariq
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Re: NES lacking audio

Post by lidnariq » Wed Jul 30, 2014 10:04 pm

... Just for curiosity's sake, what's the voltage on the BJT's emitter?
given that you mention 2.43V on pin 10 (which should be the same as the BJT's base), I'm guessing 1.75V or so?

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K_Devel
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Re: NES lacking audio

Post by K_Devel » Thu Jul 31, 2014 12:21 pm

From pin 10 to emitter I get 2.28v

lidnariq
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Re: NES lacking audio

Post by lidnariq » Thu Jul 31, 2014 1:23 pm

From pin 10 to emitter you get 2.28V? So from emitter to ground you get 0.15V? That's very not good, the BJT shouldn't be in saturation have that high of a forward voltage ever.
Last edited by lidnariq on Thu Jul 31, 2014 4:06 pm, edited 1 time in total.

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K_Devel
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Re: NES lacking audio

Post by K_Devel » Thu Jul 31, 2014 3:25 pm

Yes that does seem to be the situation.

lidnariq
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Re: NES lacking audio

Post by lidnariq » Thu Jul 31, 2014 4:06 pm

Looks like you should try replacing the BJT. The 2N3904 doesn't have the same pin order as the SMT BJT, so you'll have to be a little clever.

If you can, I'd try to use alligator clips or some sort to test it before soldering.

lidnariq
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Re: NES lacking audio

Post by lidnariq » Thu Jul 31, 2014 4:09 pm

K_Devel wrote:The leads touched on the blue portions, bout 0.13v
... wait a moment, the two blue pins are ground on the left and +5V on the right. What?

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K_Devel
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Re: NES lacking audio

Post by K_Devel » Thu Jul 31, 2014 5:18 pm

lidnariq wrote:
K_Devel wrote:The leads touched on the blue portions, bout 0.13v
... wait a moment, the two blue pins are ground on the left and +5V on the right. What?
Ok, something weird just occured, and this never happened before. I put the multimeter to B and C and suddenly audio came out. It's producing 4v.

Lemme show you what poInts I can touch and audio comes or comes out weaker..

Purple is full audio, sounds great.

Blue is weak, sounds staticy, wager cuz of the resistors between those points there. I dunno

However.. audio.. is coming out.. when I touch stuff. What?

Image

lidnariq
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Re: NES lacking audio

Post by lidnariq » Thu Jul 31, 2014 5:43 pm

The places you are getting audio are mostly places you "shouldn't". ... a little may show up in the regulated +5V, but shouldn't very well ... at least, there shouldn't be any more there than video signal, because both inputs start with the same BJT buffer. If you're getting significant coupling of the audio to +5V ... and +unregulated ... it does make it look even more like the BJT is toasted.

Anyway, here's a loose schematic for the non-modulated outputs of the RF module:
Mitsumi NES RF modulator baseband schematic.jpg
The places you "should" hear audio are along the white path. Cyan is the video path.

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K_Devel
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Re: NES lacking audio

Post by K_Devel » Thu Jul 31, 2014 6:15 pm

so, looks like I'm desoldering and putting on a new transmitter? Bawwwwwwwwww.. well, whatever fixes this. I'll be happy if this is the ONLY problem with this thing. If it goes beyond this, it's almost worth just rebuilding the damn thing w/ only composite video and audio and just nixing all the RF.

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