My favorite method for finding the reason for such problems:
The Process of Elimination:
- Try your charger on another DSi(XL) or 2|3DS(XL) console to verify the charger is working
- The other way round: Try another, known good, charger on your DSi
- Charge your battery in another, known to be working, DSi to verify if your battery accepts charge
- Provide a know to work battery in your DSi and see if it charges
After these tests you should know if the charger, the battery or the console has a problem.
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For the case the trivial replacement of battery/charger doesn't help; Possible reasons for the console itself not charging (see photo below):
- Charging port damaged or loose connection/bad solder joints
- Measure voltage on the inner solder joints with charger connected. Gently push the connector in all directions to see if it starts charging when applying a little(!) force. Replace connector if needed
- Fuse F1 blown
- Measure continuity. If the fuse is blown, replace it (and hope it doesn't blow right away). Be warned this thing is tiny. Not an easy solder job. You can also bridge the fuse: Much easier, but dangerous for the board. I advise against bridging fuses.
- Filter(?) EM1 defective
- No idea how to check it. Measure voltages of a charging working unit and compare it to yours. I have no idea what part this is; I would use a donor board to get one
- Power board not correctly connected(and I think the power board has a fuse as well)
- See if you get battery voltage on the white connector at the bottom – the small metal points next to (+) and (-) markings on the mainboard.
- Charging IC defective
- Same as EM1. Last thing to do. If everything else is okay, I would suspect this little chip. Requires rework station (hot air)
F1 is right below the charging port, EM1 left to F1 and the charging IC is inside the red box in the following picture: (The photo is part of a blog entry I posted months ago, so ignore the text)