Gaming GBA SP (AGS-001) no sound

[romanaOne]

I have been trying to get the sound working on an old GBA SP and nothing seems to help. It is not a contact problem with the speaker: I tried 2 speakers and tested both of them with a multimeter (both are about 8ohms). I tried cleaning the power/phones port and there is no sound coming out of the heaphones either.

This makes me think the volume control may be the fault. What is that thing? A variable resistor? If so, 5KΩ ? 10 KΩ? Something else?
Can I just put a resistor or a wire across in parallel with the slider to bypass it and test? I don't want to break the GBA worse and I don't even know
if the slider actually is a rheostat.... It is soldered to the board in 6 places. Which pins should I measure across / jumper?

 

[FAST6191]

Usual first test is to see what goes with the headphone socket. If it has triggered the "is plugged in" button (which is often just a thin metal tab that gets bent, even on far more expensive devices) then this will show this. You can fish around with a pick if you want to bend the tab back, though in most other devices I have seen plugging the headphones in will bend it back again.
That said if you plugged headphones in then they would normally work.
Desolder the headphone socket if you want.

Speakers failing is a possibility but rare, and it sounds like you already have resistance across them so that is even less likely.

Variable pot that doubles as volume control failing is the main cause that is not socket woes. If you can disassemble it far enough to get a squirt of contact cleaner in there and run it back and forth a few dozen times then do. You might get it to do something again by pressing more on the wheel to either get it to part of the track that is not corroded or off its normal groove that might also be corroded/dirty.

I don't know offhand what the reference resistance/resistance range is if you do have to source a replacement, and we don't tend to have nice circuit diagrams. Indeed I was surprised to find nice PCB scans and sanding pictures for the original GBA the other year when doing ( https://gbatemp.net/threads/thinkin...fixes-compilation-thread.485501/#post-8628992 which looks like it might give you a better idea of the pinout, by which I mean https://gbhwdb.gekkio.fi/consoles/ags/ rather than the things attached).
Yeah you can bypass it with a fixed resistor or two -- if the one it is supposed to have has failed then chances are it failed open which means infinite resistance so no worries there, or if it failed closed and low then something else likely would have gone pop if that was a problem. Start high and work your way down. It is unlikely to be in the silly high ranges -- it is only a GBA and probably limited elsewhere (I don't think I have seen anybody replacing speaker volume/headphone socket limiter resistors to increase volumes for the GBA) rather than some silly rave grade pro audio setup that would benefit from high.

 

[romanaOne]

Well, I got brave and just took some wire and connected pins 5,6 but still no sound. I'm guessing 1,2,3,4--located at the ends of the metal box--are just to hold the thing on the board.

Measuring with the multimeter set to 200Ω scale, I'm getting very little resistance between 5,6 (less than 1Ω) and off scale between 1,3 2,4 2,3 1,4. This could just be due to 5,6 being closer together and the metal box conducting..... Anyway, the position of the slider doesn't seem to matter. I wonder if all 6 solder points are just to hold the pot to the board and maybe the actual electrical connection is under the metal box.

Looking at the pictures of GBA SP boards linked above, I notice that U3 is an amplifier. There was some kind of residue on the board around its pins, but most of it washed away with isopropyl alcohol. I got this GBA "for parts" and it was super-dirty with a swelling battery so I don't really know what it has been subjected to. There could have been liquid shorting those U3 pins.....

Maybe I'll give the contact cleaner a shot, once I get some more...