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[RTL8710CF] How to Reflash Firmware on Kasa KP400 WiFi Exterior Smart Plug (US)

Jerther 984 6
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  • KP400 teardown and RTL8710CF pin template

    #1 21687589
    Jerther
    Level 5  
    Posts: 30
    Help: 1
    Rate: 9
    Hi!!

    Here's another guide for a Kasa device!

    You will need to crack the device open with some cutting tools and say goodbye to its IP64 rating... Be Careful; I knocked off a small cap and I had to replace it. 2.2 µF 400 V is not exactly common.

    The process is the same as in Kasa's other devices, for example: https://www.elektroda.com/rtvforum/topic4098414.html

    The pads are clearly labeled on the PCB.

    The screws need a small torx bit. Not sure of the size. I think it is T8.


    Disassembled electronic device with power cord and visible circuit board

    Interior of dismantled electronic device with visible PCB and wires

    Close-up of PCB with thick copper traces and a highlighted SMD chip section.

    Close-up of a circuit board with relay, capacitors, and colored wires.

    and here's a basic template I came up with:

    
    {
      "vendor": "Kasa",
      "bDetailed": "0",
      "name": "Kasa KP400 WiFi Exterior Smart Plug (US)",
      "model": "KP400",
      "chip": "RTL87X0C",
      "board": "TODO",
      "flags": "1024",
      "keywords": [
        "TODO",
        "TODO",
        "TODO"
      ],
      "pins": {
        "2": "LED_n;2",
        "3": "WifiLED;0",
        "7": "Rel;2",
        "8": "Rel;1",
        "9": "WifiLED;0",
        "10": "LED_n;1",
        "11": "Btn;2",
        "12": "Btn;1"
      },
      "command": "setButtonTimes 50 1 5",
      "image": "https://obrazki.elektroda.pl/2201733400_1757640007.jpg",
      "wiki": "https://www.elektroda.com/rtvforum/viewtopic.php?p=21687589"
    }
    
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  • Boot log confirms AP mode and DHCP assignment

    #2 21687649
    divadiow
    Level 38  
    Posts: 5174
    Help: 443
    Rate: 908
    nice.

    here is boot log from backup you sent (with obvious differences it not being real device) plus a device joining the TP-Link AP it broadcasts
    Code: Text
    Log in, to see the code
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  • #3 21688039
    Jerther
    Level 5  
    Posts: 30
    Help: 1
    Rate: 9
    I suspect there's a power meter in there but there's no mention of it in the device documentation (although there's not much in there anyway)...

    I'm not sure how to verify that. I'll have a look at the other chips on the board.
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  • #5 21688968
    Jerther
    Level 5  
    Posts: 30
    Help: 1
    Rate: 9
    BP2525: step-down constant voltage driver chip. It's located just under the power supply section so I guess it makes sense.
    SP5: this should actually be a SSM6J505NU, which is a Silicon P-Channel MOS (MOSFET). I believe it drives the WiFi antenna.

    Welp, no power meter related stuff that I can tell. Bummer ;)
  • Silicone reseal and clamped reassembly for waterproofing

    #6 21695111
    Jerther
    Level 5  
    Posts: 30
    Help: 1
    Rate: 9
    Some pictures of how I did the reassembly. In an attempt to recover SOME of the waterproof quality, I sealed the case back with some Permatex Black Silicone adhesive sealant I had left from another project.

    I used masking tape because that silicone stuff is really messy. I removed the tape while the sealant was still wet, and I used a clamp to make sure the front was tight.

    Permatex black silicone and hand tools next to taped object being sealed

    Camera secured to table with a woodworking clamp
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Topic summary

✨ Discussion about reflashing firmware on a Kasa KP400 US exterior WiFi smart plug based on the RTL8710CF platform. The device must be opened by cutting the enclosure, which destroys the IP64 sealing, and the PCB pads are clearly labeled for flashing. A boot log from the device shows TP-Link IoT Platform KP400(US), software version 1.0.4 Build 240305 Rel.111944, hardware version 3.0, and RTL8710C bootloader details. The board was inspected for a power meter but none was found; identified components include a BP2525 step-down constant-voltage driver and an SSM6J505NU P-channel MOSFET. Reassembly was done with silicone sealant to partially restore waterproofing. A later note mentions retrofitting a KP401 with an ESP32C5 and disabling the RTL8710CF.
AI summary based on the discussion. May contain errors.
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