Flashing Openbken on TUYA E14 9W Smart Bulb with CB2L, BK7231N Firmware V1.5.21 from AliExpress

I got this bulb from AliExpress.

The bulb uses new patched firmware V1.5.21, so Tuya-Cloudcutter is not an option here.



Disassembling the bulb is easy, and I was able to take it apart just by hand.



It uses CB2L, BK7231N, which needed desoldering to access the flashing pads.



P24 - PWM 5
P26 - PWM 4
P8 - PWM 1
P7 - PWM 2
P6 - PWM 3

I did flash Openbken successfully, but I had problems when I put everything back.
The bulb was very slow when opening the configuration page, and it crashes and restarts. I thought maybe the flashing went wrong, so I desoldered the module again and flashed it with another old version of Openbeken.
The module was responsive when it's powered outside the bulb, but when I installed it again, it showed the same issues.

I then tried esphome, and the same issue! So maybe I got a bad power supply board or something?
I didn't do much testing when I first got the bulb, so I don't know if it was faulty from the start or not.

I also tried replacing the module with ESP32-C3, and it showed the same symptoms. I left it powered on for the night, and the next day it was working with ESP!
I'm leaving it now with the ESP as it's still running fine till now.

Hello, have you tried OBK with Power Save? Have you tried to do RF partition restore?

I didn't try Power Save, but I did an RF partition restore.

If the module was responsive outside the lightbulb, it also points towards the power saving.

This looks very similar to the "upgraded version" E27 lamps I got from eBay. 6 pins to the lamp board but only 4 used. + & - voltage and I2C clock and data. Once I had the clock & data sorted and removed the rogue PWM settings and enabled the KP18058 driver, they started working as best they could. My lamps are RGBCW though, but I think you mentioned it's all done over I2C, so maybe the same way of data addressing.

Just an idea to throw out there.

I just received the second bulb from the same seller.
This one seems to have issues too with the Tuya app. I was able to add it one time, then it disconnected and won't add again to the Tuya app.
I will flash it with Openbeken and see if the power save works.

Looking at the pictures you uploaded, the WiFi antenna part of CB2L looks as if it will hardly stick above the level of the LED PCB when it is attached. I wonder if the WiFi signal is getting degraded?
In some older lamp units I have, the WiFi antenna is just a wire that sits above the LED board and they work well, but the new CB2L boards with built-in WiFi antenna suck big time. I wonder if we can cut the onboard antenna and just replace it with the correct length piece of short wire to improve the WiFi signal. That may be my next test to try when I get 5 minutes to explore the idea.

I'm still thinking it has something to do with the power supply.
For the second bulb, I had an issue pairing it with the Tuya app. I removed the CB2L and connected it to an external 3.3v supply, and it paired with the Tuya app with no issues.

I flashed Openbeken, and this time it's working great so far without enabling power save. But I did put a startup command to enable it just in case.

PowerSave works. I just had to fix a plug that had no PowerSave enabled and the step down converter there (230AC, or, should I say, 325DC -> 12V) degraded capacitors so quickly that it failed after half a year without PowerSave. See the fix I had to do, I had to replace the capacitor, it even wasn't visible damaged, but device had only LED always on dimly, without OBK booting:

And of course you have to use low ESR capacitors for that to work...