No sound on right sound channel (ADPCM fixed)

[BlueBMW]

just to clarify ADPCM works (well in the left channel at least). So the issue now is just no sound in the Right sound channel.

This is on both the headphones port and through the A/V out?

I chased around a right channel audio problem for a LONG time on my Duo... turns out the right channel connector on my TV was wonky...

[Duo_R]

correct, the ADPCM problem fixed, now just right sound channel (lol). I am positive it is an issue since headphone jack and AV port both don't output it.

[Charlie]

(Well, I was hoping for a more definitive answer, like "Yes, the audio does definitely disappear when I short...", etc...but I will assume that the answer was YES, THE AUDIO DISAPPEARED in both cases.  I want to make sure we are not confusing the ADPCM audio source with Game Audio, External Device Audio, or DAC Audio, etc)

As I said, U504 pin 5 is where the monoaural audio becomes "stereo"; it is actually only two-channel monoaural audio.  This pin connects to a common point on R629/R627.  (Right channel first component, left channel second component).  These two resistors feed the two identical R & L circuits.  Audio now into U506-6/U506-2.  Out U506-7/U506-1 to C604/C610.  Through R608/R610 to AudioJack JK601-5/JK601-1.

We can stop here for now, as any sound not at the  AudioJack pins will certainly not make it any further anyway, although we still have to check to see if the problem is actually further down.

As I have previously mentioned, there are various mute and anti-pop circuits in here also.  It so happens that there is one such circuit in this area also...so it may be that the right channel "turn off" circuits are malfunctioning and killing the audio, even if the actual amplifier circuits are ok.  We'll check that after you give the a definite answer on the above path from U504-5 through the rest of the points to eventually reach the AudioJack.

I assume you can unsolder a few parts if we need to...and replace them undamaged?

Ever think of getting an o'scope?

Charlie

[Duo_R]

Charlie thanks a ton again for your help. I have been away on business a couple days but will give this a shot this weekend. I don't have an o'scope, but I think I do want to eventually get one. Any ideas which would be an affordable but good one to use?

As far as SMD parts, yes that won't be a problem to replace parts. I am confident I could remove a HU6260 without breaking a pin.

[Charlie]

OK, fine.  I'm going on vacation myself for the week of Thanksgiving, so I won't be back until next Friday.

If you still can't get audio out the AudioJack, remove C671 (right, C70 is left).  This will disconnect the circuitry further down the amplifier chain; if the problem is down there, it will be unable to affect the AudioJack audio, so if you get the missing audio back, you know the problem is after C671/C670... if you don't get audio back at the AudioJack, you will have narrowed the problem area to about 1/2.

I don't think you will get it back, however, because the circuitry further down, even if flawed, only has a small effect on the AudioJack. 

Next, try removing transistor 603 (right, 604 left).  This is the "turnoff" circuit.  By removing it, you will have disabled the turnoff, which obviously means it should turnon!

Good luck, see you in a week.
Charlie

 

[Duo_R]

Ok Charlie, I am definitely getting somewhere with the no audio on the right channel. I did some measurements and here are the results:

C18 - 3.19V
C17 - 3.2V

C614 - 3.87V
C613 - 3.31

C610 - 5.23V
C604 - 1.398 V

so obviously an issue with C604. The voltage was significantly different. So I then did a jumper using a 1uf non-polarized cap between C610 and C604. The result, I had sound in both sound channels. Doing the same L/R jumping between C614 and C613 did not change anything (still no sound in right sound channel).

This concludes the problem is between C610/604 and C614/613

So next I did a measurement on IC506.

Pins
1 - 5.27V (OUT)
2 - 3.88V (IN)
3 - 3.88V
4 - N/A
5 - 3.88V
6 - 3.32V (IN)
7 - 1.38V (OUT)
8 - 7.75V

So here you can see that the 4558 opamp is not outputting a signal at the same consistent voltage level as what is coming in for input 1 & 2. Going in, the signals are pretty close, but going out the voltage measurement shows there is a significant difference for the right channel.
 
Now I swapped in this 4558, so I doubt that it is a bad part. I could swap another one in, unless you think there is something in the circuit that is causing the 4558 to output a low signal for pin 7?

I haven't tried removing the parts you suggested yet, not sure if where I am getting the signal to work would make the assumption that removing that would do anything. Let me know what you think.

[Duo_R]

another update - removed the cap C671 and didn't have any changes.

[Duo_R]

another update, removed transistor 603, no change. I have looked over the board with a magnifying glass, nothing looks bad. time to test the resistors and other small parts in that area of the circuit?

[Charlie]

Well, since you believe that the circuit around C604 is the problem, first check R692.  It connects between U506-7 and U506-6.  (R691 for Left channel).  It may be cracked, etc....actually, any problem in the path from U506-7 back to R692 and on through it to U506-6 could cause this.
 
Second, check R629, same as above.  It connects between U506-6 and the audio source at U504-5.

Third, check your soldering on U506 pins; make sure removing the old IC didn't break this path, even while NOT breaking the path into C604.  Also make sure there is no flux residue, etc, that could be providing a high-impedance path.

It is also possible that the incorrect voltage is cause by one of the other circuits feeding that IC.  Remove R613, R616, R630, R690 and C604 (all of them as a group...keep track of which is which!).  This should leave on the IC itself, R692 and R629.  Does the voltage become correct?  (It almost HAS TO, there's nothing else there to cause the problem!).  Either way, you're down to only three parts and their associated circuitry, to work on.

When you are eventually able to get the correct voltage, re-install C604 first.  This will let the (hopefully repaired) audio finally get to the Audiojack and the headphones.

 Then go back and reinstall R613, R616, R630 and R690, in that order.  Check after each one to see which cause the correct voltage to go bad (and presumably, the audio to go away).

[by the way, you said:
C18 - 3.19V
C17 - 3.2V
did you mean C618 and C617?]


Charlie

Edit: Hey, why did you check the voltages on those first four caps...they are not part of the ADPCM!?!?

[Duo_R]

Thanks for the reply I will try that. Yes I meant c617 and c618.


[by the way, you said: C18 - 3.19V C17 - 3.2V did you mean C618 and C617?]

[Duo_R]

Well they are a part of the L/R circuit correct? My adpcm is apparently working now.

Edit: Hey, why did you check the voltages on those first four caps...they are not part of the ADPCM!?!?

[Duo_R]

it's fixed!!!! It's fixed!!!! Hallelujah!!!!!

Pin 5 on the 4558 wasn't properly soldered back on when I did the swap. I cannot believe it!!!! Full stereo sound and ADPCM fixed!!!! Damn Charlie you are the man!!!!!!!!!!

[Charlie]

==>Well they are a part of the L/R circuit correct? <==
They are part of a DIFFERENT audio source.

Someday I should probably make the schematic of this circuit....it generally appears that the audio seems to be a pretty common problem.

-------------------------------
Here's a side thought, which may actually qualify for a different thread....
What do you think of making a TG16/TGExpress/Duo full development station?  I mean the hardware that will give you full control over the CPU, address breakpoints, single stepping, data display, etc.  You could certainly make/change programming really fast when writing that "killer game"! It would mean cutting into a working unit, although you could certainly restore it.  I just wonder how much interest there would be in this vs how much usefullness, given the availability of things like Medafen, etc.

I'm also considering making a TG-based prom emulator (cheap!) that can be loaded from the parallel port of a typical home computer and look like an HUCard....but how many of them come with parallel ports these days?  This would be easier/faster than programming a prom chip in an external programmer, then plugging it into some kind of HUCard equivalent, etc.  I know there are similar things out there (USB based), but they are somewhat expensive.

Any other thoughts, hardware speaking?

Charlie

[TheOldMan]

I don't think a full-blown development station is worth the time/effort. It's fairly easy to check the code in one of the emulators, and I can usually manage to figure out what's going wrong without single-stepping the code.

However, I would -love- to have a prom emulator. That would allow us to hunt down / fix bugs that the emulators just don't reproduce (like video snow, due to VRAM writes....)  I would suggest that it be 2 boards, though; one 'master' board that does the prom emulation, and a second board to handle the I/O to/from the pc. That way, if your pc has a parallel port, you can purchase that version of the i/o board. And, if you lack a parallel port, you can purchase the USB version.

The only real problem I foresee is that some people are going to treat this as a flash cart, and trash talk it since it only holds one game :-)

[Duo_R]

Audio schematic would rock and be a great sticky thread.