Weird Joycon Charging

Nintendo Questions Nintendo Switch
1

Hello everyone,
I have a 1st run unpatched (sn#xaw1007) on stock firmware. My switch went unused for awhile and last week I got it booted up and updated controllers/dock etc and installed advance wars. However I noticed the left Joycon was almost dead and not charging. Seeing as this is old hardware I figured the Joycon batteries had given up, and got some replacements on Amazon and installed them no problem.

Next I notice the left Joycon still isn’t charging, and the right one will only charge when system is unplugged or undocked. so I research and find out the fan is on the same charging circuit but my fan works still, not sure if it’s full speed as I remember but it’s on.
I then tried the Hori control pads and the left unit is not working which means I assume the switch is not powering or communicating with the left rail, even after disconnecting/re-pairing etc.

Not wanting to lose my saves and seeing how this was going I went out to local GameStop and got an oled switch and moved my saves/games over to the new system so this one is just for science now.

I then re-initialized the console and now when I put both Joycons on the switch, plug in the oem charger and unplug it the right Joycon starts charging but the left joycon charging icon flickers from charging to battery level and just stays showing level. The only way I am able to charge the battery is to disassemble the Joycon and switch the batteries.

I am not finding much info on this issue and am wondering from someone with better understanding of the Joycon charging circuit if this is worth tackling on component level or is it just easier to put a whole new motherboard and get new Joycon (the left one acted up after the 3rd disassembly and the sync button stopped working). I wouldn’t want to put a new mobo in and still have the issue so any input you can provide is welcome, thank you!

TL:DR
-First gen unpatched switch on stock firmware fan still working not sure if it’s 100%
-left Joycon was dead, bought new batteries and still left was not charging, swapped batteries to charge.
-joycons are not charging while plugged into the power adapter, only when un-plugged
-initialized the console and now the left Joycon charging icon flickers for a second but returns to battery level and not charging.
-Need to know if it’s worth diagnosing on circuit level if there is enough known, or just buy a new mobo and joycons.

Thanks again!

2

Forgot to add that nothing is disconnected internally or obvious burnt looking on the back side of board I didn’t remove it from case, just removed cooler for a look, then re-paste and re-assemble.
Also when doing the disconnect/reconnect of Joycon the switch still shows the slide in animation for the left side so it knows that it’s connected just no power.

3

is the fan working or are you noticing that things are getting very warm? On the very early revs of the board there is a small diode directly behind the fan connector. This thing often fails and stops the joycons from charging and the fan from spinning. You can just remove this diode as it is not needed (and was removed in later revs). Had one on my bench yesterday with the exact same problems (and it was my third board in total with this issue).

EDIT: just noticed you said your fan still works, still might be worth looking at this diode. I know there are some small IC’s labeled PU for each joycon that I do believe have something to do with power delivery for your joycons. Also another area to look at.

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Ty! I do feel the air moving from the fan but I am not sure it’s full speed.
I will check out the diode and report back if board has it and if removing it helps.