NES lacking audio

[lidnariq]

That sounds waaaaay too low. Try removing one of the capacitors I mentioned.

[K_Devel]

Removing the 39µH inductor now produces sound, not only that, it's boosted sound. It sounds normal coming out of pin 10 now. Should I just connect the area from FC1 that is now empty into C4 or is there something else that needs to happen here before we snap this up?

[lidnariq]

Nah, removing the 39µH inductor just established that the reason that the amplifier wasn't working was something was shorting it out further down.

Is this the board that you removed the RF modulator from? Look around for any place you could have shorted something out, or heat damaged something.
The most accessible culprit is C4, so try removing that.

[K_Devel]

Is this the board that you removed the RF modulator from?

Yes, I'll check all that now. The RF modulator is reconnected but only because I was having problems, I'll have to desolder it again to get inside box. However it'll be easier this time, I got a nice Hakko desolder gun, no more manual handpump.

[K_Devel]

I disconnected the outside box's audio pin (pin 4, chip side up), put the inductor back in, in fact I pulled one from one my parts board, just to be sure, I added a new C4, the end point where it would go to the outside box does not produce audio.

So this is what I did, I soldered the 39µH inductor to a 10nF capacitor, then I put it on my RCA audio cable, played audio just fine. Ok, so now I have the inductor soldered into the entry pin of the signal, but not soldered into the exit point, and a 10nF capacitor soldered to the end not connected to the traces anymore. Picture might better explain this, but it does provide audio out from the end of the 10nF capacitor. Perhaps trace damage between the two. Last step would be connecting it to the outside box, but this is where I'm at.

[l_oliveira]

Bottom part is the circuit inside the metal box.

[K_Devel]

I changed out the outside box, still no audio, so now I'm peeved after all that lol.. damn it.. I'm still getting audio just fine out of the lil setup I did there in the picture above. I dunno what to do, but I'm gonna have to work the outside box setup to be more modular so I can work on it rather than having it soldered to the board and being pretty inaccessable. At least I soldered the grounds a little loose in case this happened.

Think it would be ok if I perhaps setup some smaller headers so I could power this thing with breadboard female to male wires? It would certainly make it easier to work inside this box now. I'm almost 100% there is simultaneously a broken trace somehow between FC1 and C4, so that was solved like explained above, now the audio pin isn't outputting audio from the outside box, sooooooo.. yeah I need to set this up so I can take it apart and put it back together easier.

TL;DR, Is it ok if I change the 5 pins that come from the outside box so I can support some female/male breadboard wire?

[l_oliveira]

Have you followed lindariq suggestion ? The schematic I just posted shows that after the inductor there's only the capacitor mentioned earlier.

So it can only be a short on that capacitor or a botched solder on the metal box connection.

[K_Devel]

ah, I hadn't figured that may be the ONLY problem, plus I hadn't gotten the outside box off again until now so it was kinda last resort situation, as it is now, also kinda weird that this problem is in TWO outside boxes. Bummer.

At any rate, I have other systems I have to work on and if this outside box is an issue ever again I'd like to have a solid system to hook it up to and unhook it from. Is the breadboard wire ok to power it and transfer all the video/audio to the main NES board? I could still find some use out of that idea for further diagnosing some of these problem boards. I'm thinking it would be fine to build something modular with them, no gauge issues.

[l_oliveira]

It's really a lot simple to debug the circuit inside the box. While the diagram I posted only accounts for the RCA plug audio path, internally it taps audio (somewhere before the transistor) for the RF modulator audio circuit.

Since you say that the box isn't the issue, the only thing that could be causing problems is the trace that goes to the box and the tiny capacitor near it. You know how to measure ohms so, while you have the 39uH inductor disconnected just scratch solder out of the shorted trace until it measure "infinity" from the sound trace to GND.

[K_Devel]

ok, here is where I'm gonna be a little lost since I've got no SMD experience and it's a little, nerving to say the least (kinda blind). Are these the capacitors we're speaking of here? Or are we discussing the seemingly MUCH EASIER and less scary lol.. what looks like C25 inside the metal box? Bearing in mind I'm only really concerned with audio out on RCA, if RF can't happen, welp.. oh well.

btw the box IS the issue, I tried it on a system known to work 100%. I got no sound out of either outside box on that system so banging my head against the wall wasn't helped by BOTH of these outside box having this problem. I have eye sight problems too, so seeing tiny stuff is a real pain. I am hoping this isn't gonna require some delicate work with the SMD portions of the board, nor do I have replacements, so if I DO have to replace capacitors, it won't be SMD replacements, will have to route them outside of the box, tape them down or something after.

but yeah, Im having trouble seeing the backside of the board really well and not helped by the fact that I'm not terribly well versed in hardware, although I am trying muchly. Very jammed. I am making a few assumptions on the SMD here, so I'll take a picture of what I think is what here, marked in red, capacitors I believe deal with audio.

[K_Devel]

Looking at the schematic, there is the 1nF, 10uF and 47pF inside the box for the audio. The 1nF is directly after the main board's 10nF that goes to the pin to the box. Could i possibly just add new capacitors on top of the SMD without removing? I have all the non-SMD replacements, but I gotta say my eyesight is caca and magnifying glasses make me go cross eye'd when I try to get a closer look.

Referencing this for a bit now:

[lidnariq]

Simply adding a new capacitor won't fix things if the current capacitor is a short.

It's the tiny brown square in the top left of your picture, that you've marked with a red dot. Removing SMDs aren't too hard, and the hakko should make it easy. The only tricky part is minimizing collateral damage, given the 270Ω resistor and BJT right next to it. Tweezers or thumb forceps are the best tool here: they're small enough to hold things in place while you carefully apply heat to just the right place . Or it's remotely plausible the hakko came with a tweezers attachment, if so, use that.

I bet you don't actually need to replace it, but if you find it matters you could stuff a little disc capacitor in here later.

[K_Devel]

Hakko 808 comes with a big box of nope on the tweezers, though I have some. Maybe I could use nail clippers to brace it perhaps. The closeness of the work has me worried. I never intended on really doing SMD work because of how crap my eyesight is. I could, just go for it. This board is easier than the other one I pulled, it has much more busyness on it, heck, I can't even follow it really, too compact for my eyeballs indefinitely. I'm hoping the 1nF I toss in this doesn't cause any clearance issues, I would rather not HAVE to route it outside it.

[l_oliveira]

Wow is the right one from a PAL NES ? (lol)

I know the one on my NES look like the one on the left.