Left joycon shows on-screen connect animation but does not connect at all

Nintendo Questions Nintendo Switch
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Hi!

Been wondering the forum for a while trying to read some topics about similar problems on switch’s, but so far, I didn’t get this one fixed. Made an account in the hopes that somebody could guide me in the correct path :slight_smile:

I have in my hands a HAD-CPU-001 board that came for no image. With the ampmeter i could see that the switch was charging and booting normal, but no image. Opened the console to see a few spots of liquid damage including a burned out flex and connector for the backlight. After cleaning up everything and getting a new screen on, the console now turns on, i get a image and everything works fine. But, the owner managed to somehow to do a reset on the console. I’m now stuck at the “joycon connection” startup screen. Why am I stuck? Because the switch only recognizes my right joycon fine. If I slide the left one in, the animation on the screen will appear but no connection will be made. If I remove that same joycon, I get no animation (kinda strange tbh). I went into maintenance mode and the joycon doesn’t appear as connected.

Already swapped the rails for 2 new ones, same problem, replaced the PU chip (which alot of people talk about), same problem. The fan works no problem. The joycon works too, but even after replacing it with a know good one I still have the same problem.

Checked the connector under the microscope and all seems fine. No flux/residue inside or burned. Did some continuity checks on the motherboard joycon connector to see if there were any other lines that weren’t supposed to be shorted to ground, but nothing, all seems OK.

What would be the next step?

I have a video that shows the exact problem and a image that show’s that the joycon it’s not connected, but can’t seem to be able to post them here.

Thanks and happy christmas guys!

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Hi, have you checked for continuity against the connector pads on the console motherboard? If everything matches out from a continuity point of view, I would check in diode mode on the motherboard pads and, if everything checks out, I would use a logic analyzer to check every data line (you can use as a known good scenario
https://github.com/dekuNukem/Nintendo_Switch_Reverse_Engineering). At this point I think you should have a better understanding of what is failing. Could you post your readings in diode mode on the connector pads on the console motherboard?

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@leoxama First of all, thanks for your time.

Second, I got it fixed! After the christmas break I took a more in depth look at the board, and noticed that a trace right in front of the connector was damaged. At first it just looked dirty and after some scraping and comparison with a know good board, I saw that this trace was damaged.

Sadly I can’t still post images, but for reference, it’s the trace with no cap, in front of the connector (on the latch side) with has a 5-leg IC right next to it.

A jumper later and the joycon it’s back at the business :smiley:

What a christmas break does!

Thanks for your help still!

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I have exactly the same problem, when I put in the left joycon, it shows me the blue animation. It works when its connected via bluetooth. But when I connect it in handheld mode. The joycon doesnt get recognized to play, but it does charge. Could you maybe send me pictures in a wetransfer link or anything?