NES lacking audio

[K_Devel]

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

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

No, all boards I have are NTSC. Most of my outside boxes are Mitsumi, this one is what looks like "Alps". It also has no bottom hole on the cover for the 5 pins going to the main board which are usually exposed both top and bottom. Although this "Alps" board is labelled nicely on the inside components. You can see the 5 pins going to the main board have nice and neat labels for what they are.



PS, I got the 1nF SMD off, managed to not burn the thing off, but my solder gun did fine propping it off after I put the hakko 808 to it to clean up the major solder around it. Adding replacement, not SMD.

[K_Devel]

So it's replaced, still no audio. Wah wah wah.

[l_oliveira]

You're doing it wrong, mate.

You're not supposed to replace parts until it works. You have to remove parts from the audio path until the short circuit to GND disappears. Once that happens test the part you just removed for integrity.

I'd toss an educated guess that the real culprit is the transistor which amplifies the audio, likely got short-circuited internally.

[lidnariq]

I'd toss an educated guess that the real culprit is the transistor which amplifies the audio, likely got short-circuited internally.

But the BJT is a common-collector amplifier connected to +5V... there aren't all that many failure points remaining to test...

[K_Devel]

I'm a little lost with what to do next, but I'm probably gonna feed the outside board 5v and see if I can isolate it from within. As it stands I saw no shorts in the initial entry to the outside board, but again, my sight sucks, maybe something is in there, maybe I'm missing something. I'll post a magnified shot, maybe one of you guys can see something actually ON the board that doesn't belong. I know visually isn't the best diagnostic, but maybe I'm missing something simple here. I feel like it's just so damn close, like great, inside the box finally, so close.

http://imgur.com/ornmA9S,kTFFtsU

So if you're interested, these images are huge, so click on them first, then make sure your browser has it zoomed 100% by clicking the raw image.

[K_Devel]

This is what I figured out so far, and I think the transistor could indeed be the problem, since it's not feeding audio out like the board I have that actually works.

The green portion is where I got audio going into, I've been able to touch point and actually hear it, expected as this is the only points where the audio from MB is coming in now.

The red is where there is no audio, but had been tested on a working board and I found they all output audio from the game, they do not output audio on the problematic board.

Replacing the transistor is gonna suck. I'm losing the form of this lil metal box if I have to keep stuffing crap in that isn't SMD. I simply don't have it, and don't believe I have the ability to solder SMD. Desolder.. sure. Hakko 808 desolder gun and Hakko solder gun handled the removal quite well w/ the capacitor.. unlike my last gun which burned the hell out of boards and generally sucked... my manual pump also sucked (no pun intended).

[lidnariq]

It is plausible that you cooked the BJT when you desoldered the RF box previously. I don't see a plausible reason why it would look like a short to ground, though.

I've been able to stuff a single TO-92 in lieu of a single SOT-23 BJT before, but it is fiddly.


Also, looking at the second picture in the imgur albums, you've got a cold solder joint on the 1nF capacitor.

[K_Devel]

I redid the 1nF this morning, it was indeed not connected. I added bigger leads cuz I simply couldn't see in there.

Green a get a signal from the audio and the 5v pin, red, I get nothing. So it's being fed power, it's getting the audio, but nothing out. Pretty dead eh? :/

[lidnariq]

Does your multimeter have a diode test mode? When the NES is off, the BJT should look like two diodes pointed from audio in to each of +5V and the 270Ω resistor.

[K_Devel]

Yeah I have diode test, it's a Mastech MS8262 Autorange and also have a 2N3904 if needed.



The leads touched on the green portions, bout 0.23v

The leads touched on the blue portions, bout 0.13v

If I even tested the right portions.

[lidnariq]

Uhhh....

Code: Select all

      C
   +-----+
   | L C |
   +-----+
    B   E

Test from B to C, and from B to E.

C-to-E shouldn't have conducted if the NES was off... consistent with the BJT being damaged, I suppose

[K_Devel]

B to C - 0.67v
B to E - 0.67v

[lidnariq]

Looks like the BJT should be working fine, then. Does the 270Ω resistor checks out nominal also?

[K_Devel]

I get about 260Ω out of it, suppose that's fine eh? The other transistor on the board reports similarly as well to the last test we did with the previous one.

[lidnariq]

When the NES is on, is the voltage from the inverter (pin 10 again) about 2V? or is it lower? The BJT current buffer won't work below an input of ~1V.