THR316D will not enter boot mode

[videobuff]

I have read and read and watched all kind of tutorials but i can't get my THR316D into boot mode so i can flash it. I is new )november 2025)
It works well with welink btw. I pressed the button and connected the USB - RS232, i held the button for 40 seconds and repowered it ,nothing. Anyone out there, who knows the golden tip ?
Erik

[sfromis]

Hopefully you have a USB/serial UART adapter at 3.3V TTL level, as "real" RS232 would be likely to destroy the chip with too high voltages. Note that some of those adapters cannot supply the needed 3.3V power for flashing.

But you did not post full and exact details of what you did to try flashing it, hence no way of guessing what you should have done differently.

[videobuff]

In full: I have removed the PCB of the THR316D from the box, soldered the four pins on the RS-232 interface, and connected it using a couple of USB-to-RS232 cables. I checked the voltages and selected the one that provides 3.3 V (actually it measures 3.4 V). The USB interface is recognized both on my Mac as well as on my Windows PC.

According to the instructions I found, I should hold the RESET button pressed, then apply 3.3 V power (the other three wires — GND, TX, and RX — are already connected). The small green LED turns on. Then I press Flash at 115200 baud for the correct port, and I have already downloaded a .bin file from the Tasmota repository. All programmes tell me they are waiting for the packet header. See the error in the pics.

ps: i have seen data coming from the current commercial firmware over the data connection, but that ended with port closed and sincde theb the same agin. I have now powered the unti over 230V , and cobbected the computer without the plus voltage.

[sfromis]

Again, your adapter (which is hopefully not RS232 which is up to +/- 15V) is pretty important, it may not be able to supply the needed 3.3V power (preferably not less than 150 mA). Your wiring to the adapter is also important. The docs has a couple of recommentations.
https://tasmota.github.io/docs/Getting-Started/#serial-programmer

In addition, it will never work with the binary file you selected, tasmota-NL.bin which is for ESP8266 when the device has ESP32. Better not download a binary first, but let the Tasmota Web Installer (which you are using) select the right one after choosing your language in the drop-down. However, it does not appear that you got far enough for this to be the problem.

I see that you also were looking at Tasmotizer, this old tool will not work for ESP32, but the Tasmota Web Installer is fine to use.

[videobuff]

thank you for your time to help me. I have flashed about 30 pieces  Sonoff and other units with this cable with Tasmota and the cable has 3.3v so I use the wrong name. But the cable is ok. I even saw data from the original software in the log screen. I have just read that this unit uses an Itead basic version which allows to update through OTA and is not so happy with serial data. Will see. I continue this morning. Met vriendelijke groetenErik SchottOp 2 dec 2025 om 00:56 heeft sfromis ***@***.***> het volgende geschreven: Again, your adapter (which is hopefully not RS232 which is up to +/- 15V) is pretty important, it may not be able to supply the needed 3.3V power (preferably not less than 150 mA). Your wiring to the adapter is also important. In addition, it will never work with the binary file you selected, tasmota-NL.bin which is for ESP8266 when the device has ESP32. Better not download a binary first, but let the Tasmota Web Installer (which you are using) select the right one after choosing your language in the drop-down. However, it does not appear that you got far enough for this to be the problem. I see that you also were looking at Tasmotizer, this old tool will not work for ESP32, but the Tasmota Web Installer is fine to use. —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you authored the thread.Message ID: ***@***.***>

[Henkonoly]

Tonight I had some time to test, and I'm afraid I've broken the first two devices myself. I took a new one out of the box and flashed it without soldering the Dupont connectors. And the third, straight out of the box, works fine.
Another thing I noticed is that the Tx LED on the TTL dongle lights up immediately on the 2 broken THR316D’s when I connect it.

So I probably let it get too hot with soldering or something.
Although both still work fine in the eWeLink app. I can update the firmware there, so they're not realy broken, but unfortunately, I can no longer flash them with Tasmota.

Suggestions are highly appreciated to still flash them with tasmota

[sfromis]

I'd carefully examine the boards for any "mishaps" causing shorts, not only at the point of soldering, but also if solder landed elsewhere. Can be difficult to spot without good magnification. Also any torn traces if you were fumbling a bit.

And with soldering, you need to be quick to get it done, without lingering. In fact, not having the tip hot enough may lead to longer time and therefore excessive heating. Of course, having the tip too hot is also a risk factor.

My approach is to have a temperature on the high end, and be very careful to be quick, no fumbling around to make the solder start melding. And to "wet" the tip with a bit of solder first, to get better heat conduction. Ideally, when soldering a pin, you should avoid the solder wire touching the tip, but instead have the tip heat the pin before touching the solder wire to the pin. Takes a bit of practice to get right.

[Henkonoly]

Thank you so much!
It's much appreciated.

I think it'll be a trash can ride, unfortunately.

[Henkonoly]

Update:

After disassembling the PCBs, I cleaned the boards and everything works now. I used a little S39, and it oxidized, causing excessive resistance between the contacts. I'll never do that again.

Thanks for the help, and have a nice weekend!

[sfromis]

Using flux is fine, but indeed better clean it off after soldering.