NES sound

[blackevilweredragon]

Neither the unamped pin nor the preamped pin get me anything.

hmm, ok, so the short is somewhere else..  give me a few minutes to find the next connection to find...  (i will use a multimeter for this, but you won't have to, ill have you tap the audio pin on something else)

[blackevilweredragon]

I would have you try both sides of this capacitor, but it's so tight in there, i worry you may accidentally short something out..  (both sides of it is the audio also, left side is louder (and is a mix of the unamped side), and the right side is softer, and is going right to the unamped pin...

http://blackevilweredragon.spymac.com/captst.jpg

[Ismail Saeed]

Both sides of the capacitor are silent.  Well, we're narrowing things down at least.

Incidentally, the component you mention with unamped and amped pins is a Toshiba thing for me instead of a Motorola thing, but it's otherwise indentical in placement on the board and in pin arrangement.

[NeWmAn]

FC1 is an L (inductance), the ceramic cap is in parallel to the NOT port (your 'preamp').
The only part remaining between the working (R6, R7) and the not working (the whole preamp thing) is the Electrolytic cap. (C23?)
Still the problem could be power on the 7404.

[Ismail Saeed]

I'm assuming the 7404 is in the AV box (or is the AV box).  I did a quick look just now to see if I could see the capacitor marked C23, and I have to admit I'm not sure where it is.  I caught sight of C22, and several numbers below it, and some numbers above it (including a C40 somewhere)... can I get a ballpark on where to look for C23?  Also... if it's an electrolytic cap, does that mean I wouldn't want to touch with with anything?

Ismail (who types his full in the Name field for the sake of consistency)

[NeWmAn]

I'm assuming the 7404 is in the AV box (or is the AV box).  I did a quick look just now to see if I could see the capacitor marked C23, and I have to admit I'm not sure where it is.  I caught sight of C22, and several numbers below it, and some numbers above it (including a C40 somewhere)... can I get a ballpark on where to look for C23?  Also... if it's an electrolytic cap, does that mean I wouldn't want to touch with with anything?

Ismail (who types his full in the Name field for the sake of consistency)

:lol: 7404

Look here:
It's the IC marked MC74HCU04  
C23 is the blue cilinder between the 7404 and the big IC.
Be careful, i'm not sure if that's the right cap, I only have the schematics, don't have a NES board to check.  

[Ismail Saeed]

So the 7404 is the thing that does the amping itself?  It's not a Motorola for me, but most of that number combination (barring the starting letter not being an M and such) is the same.

So I should test the blue cylinder's two metal legs, then, right?  Well, I tested both of them and got no sound.  After all of my tests I always verify that sound is still on R7/R8... and it is. (Just making sure I don't short anything... case in point, trying to reach the cylinder from the other side got me to reset the system)

Maybe there's something other than that blue cylinder?  But anyway, that blue cylinder isn't the problem.  It is next to the long IC with many many pins however, and that long IC is one of the most noticeable things between R7/R8 and where we're poking right now.  Should I look there next?

Should I test that IC with a multimeter perhaps?

[NeWmAn]

According to the schematics, the 12K and 20K resistors (R7 and R8) are connected together and with one side of the capacitor.
http://www.neshq.com/hardgen/schem4.jpg
The other side of the capacitor goes to pin #11 of the 7404.
If you have audio at the common point of the 2 resistors (actually 3 resistors because there's another 20K res), then you HAVE to have audio also on one side of the capacitor.
BUT... I don't know if that's the right capacitor, and I don't know if you have poked the audio on the common side of R7 and R8 or on the other side.
Poking on the other side is the same thing as poking on the 2 resistors (R3,R4) where you got your first positive result, but the 2 audio channels are separated, still not mixed.


I need blackevildragon to check his board and confirm the signal path.

Since you have the NES open, have you tried exchanging the cartridge connector?

Should I test that IC with a multimeter perhaps?

Have you got a multimeter now?

[blackevilweredragon]

According to the schematics, the 12K and 20K resistors (R7 and R8) are connected together and with one side of the capacitor.
http://www.neshq.com/hardgen/schem4.jpg
The other side of the capacitor goes to pin #11 of the 7404.
If you have audio at the common point of the 2 resistors (actually 3 resistors because there's another 20K res), then you HAVE to have audio also on one side of the capacitor.
BUT... I don't know if that's the right capacitor, and I don't know if you have poked the audio on the common side of R7 and R8 or on the other side.
Poking on the other side is the same thing as poking on the 2 resistors (R3,R4) where you got your first positive result, but the 2 audio channels are separated, still not mixed.


I need blackevildragon to check his board and confirm the signal path.

Since you have the NES open, have you tried exchanging the cartridge connector?

Should I test that IC with a multimeter perhaps?

Have you got a multimeter now?

shoot, i just put the thing back together after stereo modding mine, and the screws i have holding the case together like breaking and leaving the screws head missing...

sorry, I wasn't thinking    does someone else here have an NES and knows how to use a multimeter?

[Ismail Saeed]

Multimeter: Not at present, but the access with the person exists if needed.

Now, you say R7 and R8 should give me sound on both sides?  I do remember getting sound on one side but I don't think I got sound on the other side... I assumed that was a case of a ground like with R3 and R4.  Should I be getting sound off the extra resistor of R9 or not?

I haven't changed the cartridge connector yet, because I seem to be narrowing on the problem being elsewhere.

[Ismail Saeed]

dragon: If you stereo modded yours, that just means you tapped R3 and R4, not that you stopped it from going onward to R7/R8 etc.  In fact, I'm pretty sure the mono audio will still be at FC1 and everywhere prior to that for that matter.  So you can still test the path.  As for the case... uh, you should be able to get six new screws... what did you do that has your screws breaking?

[blackevilweredragon]

dragon: If you stereo modded yours, that just means you tapped R3 and R4, not that you stopped it from going onward to R7/R8 etc.  In fact, I'm pretty sure the mono audio will still be at FC1 and everywhere prior to that for that matter.  So you can still test the path.  As for the case... uh, you should be able to get six new screws... what did you do that has your screws breaking?

oh i know it can still be tested, but the screws are a pain, they are weakened from age..  if i try to unscrew them again, the heads break off, then i can't get the NES open again..  (2 of the screws when i opened my NES for this stuff, broke apart, and im afraid the rest will too)

[NeWmAn]

Ismail: cam you do a quick photo of R7 R8 from above?

Now, you say R7 and R8 should give me sound on both sides?

There shoud be separated audio on one side and mixed audio on the other (common) side.

[Guest]

I wasn't able to suppress the flash on my camera even if I *wanted* to, so there were several crap shots before I luckily got this high-fidelity image of what you want.

http://members.cox.net/slipgate/P9180041.JPG


R7 and R8 work on the side numbered 20K and 12K.  If I put the audio tip in just the right spot between the two on that side, I get the mixed final audio due to the tip touching both simultaneously, but if I touch just one of the two of them, I get the separate two channels.  On the side actually labeled R7 and R8, I get nothing.  I get nothing on either end of the R9 resistor.

Where should the mixed audio on the other side be coming out of, exactly?

[Guest]

BTW, that upload failed 22k or so short of where it should've, but the only part of the image that doesn't show up as a result is outside the scope of the NES in the picture.

[Ismail Saeed]

Answer me this: Can I test those resistors that work on one side and not the other with a multimeter?  How would I test them?

[blackevilweredragon]

You know, it may just be the camera, but those resistors look like they have a cold solder joint..  

[Ismail Saeed]

Well, they've never actually been soldered (after the system's manufacture in 1987/88 anyway) but looking at them I did wonder if they were somehow deficient.  However, there was dimness for the 12k resistor on the side that worked fine and no dimness on the nonfunctional side for R9 and R8 (the 12k).  The nonfunctional side of R7 is dimmer, though.  I went back down just now with a small penlight flashlight and shone the light on them from a little to the side and down... they all seemed to similarly reflect though that might be a case of massaging the lighting until I was satisfied they were reflecting.  Without the penlight, they seem to all reflect the light naturally on the nonfunctional side when I'm looking at that side head-on, but when looking from the side where the #k is printed the R7 side seems dim while R8 and R9 seem to  reflect better.  This may be due to lighting situations/my big head, though.  The 12k side of R8 reflects like the others (as long as I make sure my head isn't in the way, because the nearest ceiling light happens to be in that direction) but when looking at it from the R side seems a bit dimmer... this may be due to simple lighting/my head once again though.  The thing is, the 12 side of R8 works perfectly.  Sandwiching the RCA tip just between the 12k and the 20k there gives me full sound (incidentally, although it hasn't been amplified yet, it seems to me to be at the full volume I normally get out of the system, but I might be imagining that due to time away).

It's possible something happened to the soldering after the fact, maybe?  Would tiny dollops of solder solve the problem or just obstruct me from reaching the source of the problem?  Do we anticipate that the problem is in the cylinder of the resistor, or is it maybe on the other side of the motherboard where the resistors' point ends come out?

Now, what SHOULD I be expecting here?  I mean, R9 didn't do anything for me on either side.  Is it supposed to?  I'm not sure I should anticipate anything out of R9 or not since I'm getting both audio signals from R7 and R8 collectively.  If R9 is supposed to give me sound on either side, that can be chalked up as an issue.  If not, that leaves me just worrying about just R7 and R8 then.  Which narrows the problem down rather much, but also rather frighteningly as we come to it at last.

(Sorry for the verbosity on dimness and reflection above... I was just trying to be thorough in investigating how the joints looked to me)

Can I test the resistors with a multimeter to see if they give me 1s?  How would I do that?  Is it possible only 1 is actually broken and is corrupting the signal from the other when things come out the other side?  But wait, it's still two tips on the other side...

[blackevilweredragon]

Well, they've never actually been soldered (after the system's manufacture in 1987/88 anyway) but looking at them I did wonder if they were somehow deficient.  However, there was dimness for the 12k resistor on the side that worked fine and no dimness on the nonfunctional side for R9 and R8 (the 12k).  The nonfunctional side of R7 is dimmer, though.  I went back down just now with a small penlight flashlight and shone the light on them from a little to the side and down... they all seemed to similarly reflect though that might be a case of massaging the lighting until I was satisfied they were reflecting.  Without the penlight, they seem to all reflect the light naturally on the nonfunctional side when I'm looking at that side head-on, but when looking from the side where the #k is printed the R7 side seems dim while R8 and R9 seem to  reflect better.  This may be due to lighting situations/my big head, though.  The 12k side of R8 reflects like the others (as long as I make sure my head isn't in the way, because the nearest ceiling light happens to be in that direction) but when looking at it from the R side seems a bit dimmer... this may be due to simple lighting/my head once again though.  The thing is, the 12 side of R8 works perfectly.  Sandwiching the RCA tip just between the 12k and the 20k there gives me full sound (incidentally, although it hasn't been amplified yet, it seems to me to be at the full volume I normally get out of the system, but I might be imagining that due to time away).

It's possible something happened to the soldering after the fact, maybe?  Would tiny dollops of solder solve the problem or just obstruct me from reaching the source of the problem?  Do we anticipate that the problem is in the cylinder of the resistor, or is it maybe on the other side of the motherboard where the resistors' point ends come out?

Now, what SHOULD I be expecting here?  I mean, R9 didn't do anything for me on either side.  Is it supposed to?  I'm not sure I should anticipate anything out of R9 or not since I'm getting both audio signals from R7 and R8 collectively.  If R9 is supposed to give me sound on either side, that can be chalked up as an issue.  If not, that leaves me just worrying about just R7 and R8 then.  Which narrows the problem down rather much, but also rather frighteningly as we come to it at last.

(Sorry for the verbosity on dimness and reflection above... I was just trying to be thorough in investigating how the joints looked to me)

Can I test the resistors with a multimeter to see if they give me 1s?  How would I do that?  Is it possible only 1 is actually broken and is corrupting the signal from the other when things come out the other side?  But wait, it's still two tips on the other side...

if a resistor is working, it will report what the NES motherboard says next to it (if the multimeter is setup correctly to that range)..

[Ismail Saeed]

How strongly do you feel that the problem is these resistors?  Do you also share the opinion that the fault could somehow lie in the power supply or cartridge slot still, or do you feel the problem is definitely localized to here?

So the multimeter will present "12K" and "20K" respectively if they're working?  Wasn't I supposed to do a test for between 0 and 1?  Is it going to be a different testing mode?

Also, IS R9 going to have sound, or not?  And what is meant by the mixed audio on the other side... will it be coming out of one of the pins?

[blackevilweredragon]

How strongly do you feel that the problem is these resistors?  Do you also share the opinion that the fault could somehow lie in the power supply or cartridge slot still, or do you feel the problem is definitely localized to here?

So the multimeter will present "12K" and "20K" respectively if they're working?  Wasn't I supposed to do a test for between 0 and 1?  Is it going to be a different testing mode?

Also, IS R9 going to have sound, or not?  And what is meant by the mixed audio on the other side... will it be coming out of one of the pins?

I'm not 100% positive it's the resistors..  if you  are tapping the resistor itself, whatever the result to be expected, is what you should get..  As, you are not tapping past the resistor, but the resistor itself...  Man, that was hard to explain..

Whatever the multimeter measures, is how much resistance the resistor is having..  If it showed there was a 1, that means that resistor is blocking everything..  If it showed a zero, that resistor isn't working to well, and is just letting everything through..

remember my multimeter had a number in the 500's?  because that's the resistance for that resistor, it was the norm..  now I don't remember what setting the multimeter was on at the time, but the number wasn't in 500's, more like add some zeros (depending the setting it was on)..

[Ismail Saeed]

I'm going to wait a couple days on this multimeter thing.  Maybe get a chance to do it Tuesday of next week at latest, maybe get to do it sooner.  Just kind of busy also, which I'm sure you can appreciate as well.

I guess I'm just trying to be clear on where the points from the multimeter should be attached, what the setting should be, and what the reading should or should not be.  Maybe this'll be evident to my multimeter-using friend when he reads these messages, but just in case it isn't, I'd like to have the info on what exactly to look for and how when I do have the small window of time I can meet with him to do this in.

[blackevilweredragon]

I'm going to wait a couple days on this multimeter thing.  Maybe get a chance to do it Tuesday of next week at latest, maybe get to do it sooner.  Just kind of busy also, which I'm sure you can appreciate as well.

I guess I'm just trying to be clear on where the points from the multimeter should be attached, what the setting should be, and what the reading should or should not be.  Maybe this'll be evident to my multimeter-using friend when he reads these messages, but just in case it isn't, I'd like to have the info on what exactly to look for and how when I do have the small window of time I can meet with him to do this in.

the NES motherboard says what the multimeter should say, numbers like "20k", thats the resistance the resistor has, and the multimeter should show something similar..

you just connect the probes to, i think either end (someone correct me if I am wrong!)...  your multimeter friend should easily know how to test it..

[Ismail Saeed]

I'm looking to see if this friend can come by this weekend to test the resistors.

Let's say they ARE the problem.  Let's say that everything else is fine.  If the resistors are found to definitely be the problem, with no problem anywhere else... what would I hypothetically do then?  Would this go so far as buying new resistors and replacing the ones currently on the board with the new ones?

BTW, on the "making sure no other problems exist" front,  I'll probably have the power box tested too... what points should I use to test the AC adaptor plug and such?

[NeWmAn]

Also, IS R9 going to have sound, or not? 

According to the schematics R9 should have audio on both sides, one side would be connected to the expansion connector, while the other would go to the 7404 (via cap).
Are you sure that there isn't sound? The audio level should be less than the other (working) points, maybe if you raise  the volume on your TV you can hear something...

Let's say they ARE the problem. Let's say that everything else is fine. If the resistors are found to definitely be the problem

Resistors seem fine, the only defective resistors I have ever seen were so burned by heat that you couldn't read the color stripes on them.

The only reason why there isn't audio on the 3 res common point is that the point is somewhat connected to ground, how can that be possible... I don't know.

blackevilweredragon: I've added the resistors names to the pic below, do you think I'm right? What about my common point grounded theory?



Maybe a photo of the solder side of the circuit board can tell us something, but without a multimeter there's nothing much that you can do...

[blackevilweredragon]

I have no idea how to read schematics...    :blink:  

[Ismail Saeed]

You said:

"According to the schematics R9 should have audio on both sides, one side would be connected to the expansion connector, while the other would go to the 7404 (via cap).
Are you sure that there isn't sound? The audio level should be less than the other (working) points, maybe if you raise  the volume on your TV you can hear something..."

Well, do you mean to suggest that the volume goes way down when the two get mixed together?  I suppose I can try again at higher volume.  Now, to be clear... I didn't hear anything when touching EITHER metal leg of R9.  I heard stuff when testing the ends of R7 and R8 that are marked 12k and 20k, but I didn't hear ANYTHING on the other metal leg of those two.  When you say that R9 should have audio on both sides, does it not GET that audio until after they go through R7 and R8?  Because the other side of R7 and R8 gets me NO audio.  Is that because it's ground or is it supposed to get to the other side of R7 and R8 and THEN go to R9?  If it's supposed to be heard when I touch the other side of R7 and R8, then that's where the break is occurring since it isn't being heard there, even "before" it gets to R9.  If the other side of R7 and R8 ARE just meant to be ground and the audio is supposed to just be at R9 next, then that suggests R9 is the problem and R7 and R8 are fine.

quoting:

"Resistors seem fine, the only defective resistors I have ever seen were so burned by heat that you couldn't read the color stripes on them.

The only reason why there isn't audio on the 3 res common point is that the point is somewhat connected to ground, how can that be possible... I don't know. "

So you're suggesting something is wrong with the connection to ground?  Are they supposed to be connected to ground, or not?

Just to learn, you say "read" the color stripes instead of "see" them.  Is there something meaningful I can get out of looking at the striping?

Regarding the schematics, those schematics themselves are accurate I'm sure.  You should know though that R7, R8, and R9 are in a line like three little piggies on the board.  R9 isn't "after" R7 and R8 with an obvious "We go to you" connection, it's directly side by side with them.  From what I'm being told, R7 and R8 should give me audio regardless of which metal leg I tap.  If that's true... well, I get audio on one side but not on the other.  If it moves "up" toward R9 after that then it's already broken before it reaches R9.

What do you think of the way the solder joints look?  Suggestive of issue now?

I'm not opening the NES up again until Friday or so.  I'll do the "super-high awesome volume test" then... and I'm trying to have my friend with a multimeter come by then.  Maybe he can make it Friday, maybe he'll make it some other day of the weekend.

I'm going to have him test the power box (both its audio plug and its power, I think... what points do I attach to in order to test the power?) and those three resistors.  Anything else we should have him test while we're in there?  Since this isn't my multimeter I'd like to get all the meaningful testing done when I do get an opportunity to get at it just so it's not back and forth for some other guy to come to my place (he lives far enough away).

[NeWmAn]

You said:
Well, do you mean to suggest that the volume goes way down when the two get mixed together?

Let's put it this way: Signal exits the sound IC with a strenght that's enough to drive the speaker, after the signal has travelled trough a resistor the signal will be less.
So the more resistors the less signal strenght.

I suppose I can try again at higher volume.  Now, to be clear... I didn't hear anything when touching EITHER metal leg of R9.  I heard stuff when testing the ends of R7 and R8 that are marked 12k and 20k, but I didn't hear ANYTHING on the other metal leg of those two.

Ok, It is possible that on the other legs the signal was so muted that you couldn't hear it.

When you say that R9 should have audio on both sides, does it not GET that audio until after they go through R7 and R8?   

Yes

So you're suggesting something is wrong with the connection to ground?  Are they supposed to be connected to ground, or not?

Just to learn, you say "read" the color stripes instead of "see" them.  Is there something meaningful I can get out of looking at the striping?

They are **NOT** supposed to be connected to ground, connecting them to ground will ZERO the signal.

The value of a resistor is  written with color rings where each color equals a number so black=0, brown=1...
Anyway this is not important, resistors are fine, forget about them.


Regarding multimeter tests:
Check voltage ont the power plug, the value should match (or exceed) the value stated on the label.
Check voltage on the NES, verify that there are 5v on the ICs.
Check the AV box as suggested by blackevilweredragon.

If everything is OK then measure the resistance between R7, R8, R9 and ground: keep one of the probes touching the silver edge of the mainboard and with the other probe touch the resistors. The display should never be = 0.

If your friend can read the schematics, then show him the piece of schematic below and follow all the signal path.

[NeWmAn]

I've tried a little experiment with a famiclone (I don't own a real NES anymore): I opened it and looked at the audio parts of the PCB.
Part of the circuit looked exactly as the NES, the resistors have the same values, so I tried with the RCA audio cable to poke the resistors.
I got single channel audio from the 2 100 Ohm resistors (like you did), then I tried the 12K and 20K and got mixed audio in the common point (where you didn't get sound), but the volume was VERY VERY VERY low as I expected.
The rest of the circuit is completely different, so I can't test it further and help you with that, but if you happen to get low volume audio as I got, then you should go back and test the 7404 as blackevilweredragon suggested.

[Ismail Saeed]

Well, while there is a possibility of my not hearing "too-quiet" audio, I did have the volume up fairly well.

It was up high enough that if I had been playing Excitebike 64 I would've wanted to turn it down because of the revving sounds, though for most games it's the volume level I play at.  But then, I don't know how weak the signal truly becomes.  How much did you have to jack your volume up on your own TV before you heard it?  If it was just a few points up, then I probably would've heard SOMETHING... if it was a whole lot, then I'll try it.

So I should first see if the other leg of R7 and R8 has single-channel too-weak audio?  Or should I go straight to R9?

Ismail

[NeWmAn]

I had the TV volume set to less than 1/10 th of max and I could hear the unmixed audio perfectly, to (barely) hear the mixed audio I had to go to 50% of max.

So I should first see if the other leg of R7 and R8 has single-channel too-weak audio? Or should I go straight to R9?

You can't have 'single-channel too-weak audio', those points are all connected together. You can only have weak mixed audio, so each point will be the same.
But to avoid further confusion with R9, that has a side common with R7/R8 and one  side connected to the exp. connector, please do your test touching R7 or R8.

[Ismail Saeed]

Due to scarcity of communication, the multimeter test has been postponed to Tuesday for now.  However, in its place, I got the extra resistor testing done.

To quote Nuuma from before:

According to the schematics, the 12K and 20K resistors (R7 and R8) are connected together and with one side of the capacitor.
http://www.neshq.com/hardgen/schem4.jpg
The other side of the capacitor goes to pin #11 of the 7404.
If you have audio at the common point of the 2 resistors (actually 3 resistors because there's another 20K res), then you HAVE to have audio also on one side of the capacitor.
BUT... I don't know if that's the right capacitor, and I don't know if you have poked the audio on the common side of R7 and R8 or on the other side.
Poking on the other side is the same thing as poking on the 2 resistors (R3,R4) where you got your first positive result, but the 2 audio channels are separated, still not mixed.

Well, I tested R7 and R8 with the volume bleedingly loud.  This was painful on the side that it was single-channel audio, let me tell you (because of how freaking loud it was)... anyway, I've discovered that those resistors are okay.  On the "empty side" of R7/R8 (so named because I thought they were dead before) I get low-volume mixed audio.  I get the same on both sides of R9.

After that, it goes to one leg of the capacitor near the amp thing, right?  Well, I also heard this super-weak mixed audio on one leg of that cap (but not the other, though judging from the above that's normal).

I also heard this weak audio going into the pin you called the unamped pin.  I got nothing out of the amped pin side of it.

I believe this identifies the problem, heh.  Even so, I'll probably have my friend test the power output of the system just to make sure my system is otherwise healthy after all the crap I've been doing with it.

So, what solutions should I be looking into now?  Does the 7404 do anything OTHER than the amping of audio?  If not, can I just.... "reroute" so to speak?  Or is it not that big a deal to repair or replace this component if entrusted to properly trained people?

Apologies if the above has been told to me already, it's just getting to be a long, detailed thread :).

[NeWmAn]

I also heard this weak audio going into the pin you called the unamped pin.  I got nothing out of the amped pin side of it.

I believe this identifies the problem, heh.  Even so, I'll probably have my friend test the power output of the system just to make sure my system is otherwise healthy after all the crap I've been doing with it.

There still can be something faulty after the 7404...
That is the thing that puzzles me: the other gates of that chip are still working, it's strange that only one of the gates is dead.
Moreover if the problem was caused by (lack of) power, the other gates should be affected as well.

Does the 7404 do anything OTHER than the amping of audio?

It does other things: for example it handles the clock of the security chip.

So, what solutions should I be looking into now?  If not, can I just.... "reroute" so to speak?

I think the simplest solution would be to do the stereo MOD, you just have to add the 2 RCA connectors and solder 3 wires.

Or is it not that big a deal to repair or replace this component if entrusted to properly trained people?

Replacing the 7404 with the right tools is a 5 minutes job, a technician can also check if the part is really defective or the problem is somewhere else.    

[Ismail Saeed]

There still can be something faulty after the 7404...
That is the thing that puzzles me: the other gates of that chip are still working, it's strange that only one of the gates is dead.
Moreover if the problem was caused by (lack of) power, the other gates should be affected as well.

Well, either you or blackevildragon earlier stated that the amp itself was the problem if I was getting audio on the unamped pin but not on the amped pin, which is what is in fact happening.  I don't think the unamped pin being fine necessarily implies anything since it's going IN on that pin and I'm intercepting it before it gets in there.  The amped pin side is not coming out, though.  I don't think the system isn't getting the necessary power.

The fact that the 7404 has another duty, one that seems to be just fine (after all, I'm not getting infinite resets except when the cartridge slot casing jiggles and fudges the cartridge's proper connectivity) does puzzle me though... how can a component be "partly" fine?  I first came here * because* Iwas skeptical that the sound itself could be fried since it was on the processor and the system itself seemed fine, so the idea that the 7404 is "partly" bad and not fully bad is also similarly strange.

I wonder if maybe just the amped pin is shorted... something that maybe happened when I was first mucking with the system?

Regarding the rest of what you said: So the simplest solution is the stereo mod, even though replacing the 7404 is a 5 minute job?  Hmm.  Well, let me ask you... I've noticed that blackevildragon and I have different 7404's (different manufacturers... one of us was Motorola, the other was Toshiba - I'm not inclined to check the photos right now to figure out which was which).  How interchangeable are these with 7404's I could buy "off the shelf"?  Is this not  an NES custom part, is it really identical to replace it with another of the same kind of chip?  (I know that many parts, including the main 6502, can't just be replaced with off-the-shelf parts for a variety of reasons... in the 6502's case because of the sound)

Who would this hypothetical technician, who would know what was wrong and what wasn't, be?  Are we talking electricians?  Are we talking my friend?  Or are we talking a specialist?

[NeWmAn]

There still can be something faulty after the 7404...
That is the thing that puzzles me: the other gates of that chip are still working, it's strange that only one of the gates is dead.
Moreover if the problem was caused by (lack of) power, the other gates should be affected as well.

Well, either you or blackevildragon earlier stated that the amp itself was the problem if I was getting audio on the unamped pin but not on the amped pin, which is what is in fact happening.  I don't think the unamped pin being fine necessarily implies anything since it's going IN on that pin and I'm intercepting it before it gets in there.  The amped pin side is not coming out, though.  I don't think the system isn't getting the necessary power.

With "after the 7404" I meant that some of the parts that come after the 7404 (in the audio path), can be faulty and can bring down the audio.
It was blackevildragon who suggested checking the 7404, so it's better if you ask him    for assistance  

how can a component be "partly" fine?  I first came here * because* Iwas skeptical that the sound itself could be fried since it was on the processor and the system itself seemed fine, so the idea that the 7404 is "partly" bad and not fully bad is also similarly strange.

Please forget my comment about parts partially defective.

It IS possible that a part is partly defective and still the rest of the chip is working normally, happened to me in a few occasions.
What I meant to write is: I find difficult to believe that the problem was caused by insufficient (or not normal) power, when the rest of the gates are working.

Regarding the rest of what you said: So the simplest solution is the stereo mod, even though replacing the 7404 is a 5 minute job? 

A 5 minutes job with the right tools and a bit of experience.

Hmm.  Well, let me ask you... I've noticed that blackevildragon and I have different 7404's (different manufacturers... one of us was Motorola, the other was Toshiba - I'm not inclined to check the photos right now to figure out which was which).  How interchangeable are these with 7404's I could buy "off the shelf"?

It is not a custom part and you can replace it with another chip, with the same specs, built by whatever manufacturer you want.
The "74" family of chips are the basic components upon which the digital circuits are built.
In your case the name is composed by "74" + technology (In your case HC = High speed CMOS) + name of the device (04 = hex inverter).
Here is a page with a few links to manufacturers + datasheets:
74hcu04

Who would this hypothetical technician, who would know what was wrong and what wasn't, be?  Are we talking electricians?  Are we talking my friend?  Or are we talking a specialist?

The technician who could replace the part in 5 mins is someone who can solder/desolder ICs. Can your friend do that?
Probably an electronic repair shop can do it, but it could cost you more than a new NES.

[Ismail Saeed]

Well, with the information I have, I think what I'll do when I first get together with him is to again verify that the unamped pin works but that the amped one doesn't.  Then I'll get some multimeter testing done on the power box, the 7404, and a few other places.

He might know this, but what sort of ranges should the multimeter be set at, and what two points should it be affixed to, for the 7404, the resistors, and so on?  I won't be able to go running back and forth and catch someone here while I'm actually together with the guy, so having this information beforehand will mean that the trip will actually get some meaningful results :).

You say it would cost more than a "new" NES... do you mean another used one right now, or do you literally mean it would be 100 dollars or more?

Ismail

[Ismail Saeed]

By the way... to go back to something I said at the beginning of this thread... is it possible that the shorting was due to the Honeybee converter?  I'm just wondering if the Honeybee converter is something I should consider off-limits and never use again assuming I fix this, or if I shouldn't worry and freely use it.  I was just reading about inverters on Wikipedia, and if Honeybee converters and illegit cartridges use 5volt shocks to bypass the security chip... is that possibly what happened?

[NeWmAn]

You say it would cost more than a "new" NES... do you mean another used one right now, or do you literally mean it would be 100 dollars or more?

I meant an used NES. Is it really possible to find new ones?

I was just reading about inverters on Wikipedia, and if Honeybee converters and illegit cartridges use 5volt shocks to bypass the security chip... is that possibly what happened?

Your security chip is still fine so the converter is harmless, but you might consider posting the same question on the nesdev hardware forum (nesdev.parodius.com).

Since you are going to work extensively on your NES, as a last measure please try to swap the cartridge connector.

[Ismail Saeed]

Hey folks,

I have some testing results.

They seem to indicate that there is a potentially fixable problem here by replacing components, but that something might still be fishy.  Something very bad DID happen to my NES, seemingly without my doing.

First of all... R7-R9 seemed to test at numbers I didn't quite understand, but when I told my friend of their supposed voltages, they registered okay to him.

It would appear that the capicator near the 7404 is actually a big part of the problem, more than the 7404 itself is... however, something MAY also be up with the 7404.

The capacitor, when I reread here, apparently is supposed to have audio on both legs.  That about right?  However, I get 5v on one leg, and .02 volts on the other.  That seemed to be a problem... it seemed like the power wasn't flowing back down the other leg the way it should be... both should be 5v in the guy's estimation, but we decided I'd run those results by here to see if it was in fact SUPPOSED to be that way.  Again, according to what I heard before, both legs on the cap should give sound... however, only one does.  More strangely, the one that is .02 volts is the one that gives sound, while the 5v one does not.  Now... on the 7404... the amped pin provides 5v, and the unamped pin provides .02 volts also.  This may be because of what it's getting from the capacitor, though.  The 7404 itself is probably fine, because we looked up schematics and tested its own power usage by tapping ground and its power pin with the multimeter and got a normal reading.

My friend at first wondered if maybe such an OVERLY weakened signal was going into the 7404 (due to the cap) that it was TRYING to amplify it but was amplifying nothing.  However, I noted that amplifying what little signal it got should at least allow the weak sound already there to still exist instead of dying.  Someone here mentioned that they "barely" heard sound from the weak audio signal when at 50% volume... but they heard it, right?  My TV, as I realize now, was at a volume of 50 out of 63 to hear anything, and the friend's house I was working at was using a subwoofer that they had to turn down and then adjust back up gradually when we were switching sound test points so as to not blow it... we had to be that loud before we heard anything from the cap or the unamped pin.  Somehow, we DID hear from the cap and from the unamped pin despite both being .02 volts.  The amped pin was 5v, and as I said, this guy wondered if maybe it was trying to weaken a useless signal, but since we could get something out of it, we weren't sure that was what was happening.  So we wondered if MAYBE the 7404 also needed replacement, but it did seem more likely that the cap was having the issue that was then going down the line from there.  The 7404 itself got normal power when using its own test points, and as is obvious here (from the fact that we had another friend play Ghosts n' Goblins as we tested to keep sound going) the security chip DOES work.

There are two other things worth noting here.

1) Near the power box - http://members.cox.net/slipgate/P9040012.JPG look at the little green jut that comes down (in this image) and is between the power box and the blue plug along the left side.  In person, the silicon here apparently is a little discolored relative to the rest, convincing my friend that some of the area around the power box got really hot and burned a bit.  He pointed out some yellowizing as silicon that had bubbled up.  Some of this burning may have contributed to the issues I'm having (see #2 below) or it may have just barely been a bullet-dodge.

2) The guy tested the audio plug on the outside... he kind of did this first since I figured we may as well do it.  It reported a resistance of 1 when using the points first communicated to me in the image by blackevilweredragon.  Now, I remember asking if a resistance of 1 there meant the problem WAS there or was earlier along, and dragon said that as long as a component was fine, even if an earlier component was jacked, it wouldn't list resistance.  So anyway, there it is... a 1 resistance.  This is possibly due to the fact that the audio signal isn't coming right anyway by that point, OR it may be due to the above burning of silicon.  We were curious to test the video plug for a similar 1 rating, since the video plug DOES work, but we didn't know what the other test points out of the four in that little row for those things, and when you don't know which is which the results are hard to take anything from.  I do still wonder if the 1 resistance is due to the cap and the  7404, but it is possibly something to check again after/if those components are replaced.

However, the "burning" and such make it sound to me like the problems creeping up aren't really related to my mucking in the NES and were coincidentally not long after I messed with it.  The capacitor seems like criminal #1, and we have two other possible criminals that may be exonerated or may be found to also be guilty after criminal #1 is put away.

A stereo mod is certainly a workaround in the here and now, but the burned silicon and how and why the system overheated are important questions to me, as I may just be putting off a system death in progress rather than cheating my way out of a problem.  My friend is cautious, but moreover says he doesn't himself have the cold core soldering iron we would need even if we did replace this stuff.  (He's replaced caps on an RV a lot... it's just that he wants to play it carefully especially with a board that HAS had burn issues, and he has 99% certainty it's the cap but realizes that due to later issues that might not be the end of the solution).

Oh, and other components aren't an issue.  The silicon is very healthy in other regions (he even let me see the yellowing by having me compare the color nearer the processor to that nearer the power box on that jut)... the cartridge connector and so on are fine.  He was rather impressed at how much information I had... more than he anticipated... and also appreciated knowing that power irregularities for the NES can kill sound, because it's what prompted him to test voltages on the cap and make sure the 7404 was receiving the power it should.

So, question 1 here, which determines if the cap is at (primary) fault... are the two legs on the cap supposed to read 5 v and .02 volts?  (note... all things that read 5 volts for me actually read 5.01, but that was a variance neither he nor I worried about, especially to see them consistently be that)

Question 2 is: If the unamped pin being at .02 volts yet having sound while the amped pin at 5 v not having sound makes sense to anyone, and if his theory is possibly a good explanation or not.

He's pretty much convinced it's the cap, and thinks the 7404 and later are suffering because of it, but he recognizes the silicon burning could've affected a signal path and he'd test the 7404 again to see if that fixes the problem on the unamped pin after replacing the cap.

This is of course getting closer to territory where a "new" NES would be safer, but as long as no money or small amounts of money are the only issue here, I'd like to investigate this problem out to its end for my edification.  I've learned a great deal through you guys and through what he showed me that night.

[blackevilweredragon]

The silver points?  That's not "silicon", silicon is in the chips, and is like a dust when exposed to air..  What you are referring to, I believe, is Solder..  And the brownish color isn't burning, that appears to be either flux, or the solder was a Rosin Core Flux solder..  My game console mods always appear that way, it helps the joint stick better.