[BK7231N CBU] CCT rectangular ceiling lamp MARIPOU (UART silent)

Purchased from https://pl.aliexpress.com/item/1005005070248246.html

Unfortunately I don't have too many photos of the teardown itself, but rather nothing of interest.

Power is supplied via a 'bracket' which we screw onto the ceiling and plug it into 230V. When putting the lamp on the bracket, we put it on the bracket and rotate it until the 'spring' pins make contact. The L of 230V can easily be touched with a finger

The lamp itself has 2 flaps on the back - one secured with clips in the middle, under which the 230V cables hide, under the other secured with 2 short screws is the PCB with the CBU module.



The LEDs are powered by 5V via 2 BP2958 drivers.

The CBU is wired to 5 pins - 8, 10, 11, 13, 14. It was supplied with a new software version, incompatible with the Tuya-Cutter. According to the specification 8-12 is PWM, it's not clear to me what the third PWM PIN is for, as the output only has two channels. In the middle is something labelled "U1", I am unable to catch what this component is.

Unfortunately, this is where my teardown ends - I am unable to sflash the device. I'm using BusPirate 3.6, I'm correctly splicing MISO/MOSI with TX/RX (I've tested both variants), GND, 3.3V is supplied by an external lab power supply. Programming does not go through the "Failed to get bus!" part. I tested all 3 baud rate presets.

CBU only had the bottom pins soldered, so I rule out the presence of any MCU interfering with TX/RX. I also previously tested the RP2040 in UART bridge mode, but this again did not like the flasher downloaded from Elektroda. The UART is silent, I can't see any data.

Have any ideas on how to bite this topic?
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If nothing is actually connected on RX1/TX1 then flashing should be successful. I usually use the four wire method in such a situation, that is ground, RX, TX and 3.3V power supply, when I need to "get bus" then I disconnect the power supply for a while. Maybe the capacitors on the board hold the charge and recharge through the UART lines.

Best to solder out the CBU, but if not then try like this:
1. disconnect the 3.3V
2. turn on programming
3. short the 3.3V wire from the CBU side to GND (but the wire from the CBU side, not from the PSU side)
4. disconnect it from GND
5. connect 3.3V from PSU to 3.3V CBU
6. then maybe the programmer will catch

And if not, then standard:
- try another baud
- try another programmer (we really had reports that some UARTs on USB don't work very well)
- shorten wires

Did you flash anything else with BK using your method?

>>20885946 .
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I found a schematic of the BP2958X, it appears that it communicates over PWM with the CBU.

BP2958X circuit description:

1. brand name
Jingfeng Mingyuan

2 Circuit description
The BP2958D/BP2958F is a precision LED driver with constant current in a step-down configuration. It supports both PWM input dimming and full analogue dimming control mode, making it ideal for smart LED lighting applications, free of strobe effect and noise.

The BP2958X series provides excellent dimming linearity and high output current stability. It can be used in non-isolated step-down LED power supplies with a wide input voltage range (85-265 V AC). The BP2958X chip integrates a high-voltage start-up circuit and a 500 V power transistor, so no additional VCC capacitor or auxiliary windings are required. The minimal number of peripheral components enables very good current stabilisation performance, while reducing the cost and size of the overall system.

Inside the BP2958X chip is a high-precision current sampling circuit, which guarantees accurate maintenance of constant output current for the LEDs and excellent supply voltage stabilisation. In addition, the chip is equipped with a number of protection features, including broken circuit (open LED) protection, LED short circuit and thermal regulation. The BP2958X comes in a DIP7 housing.

3 Features

Supports analogue dimming from 1-100%
Full analogue dimming without strobe effect
No need for a start-up resistor and VCC capacitor
Integrated 500 V power transistor (lamp)
Accuracy of LED output current: ±5%
Open-circuit protection (LED)
LED short-circuit protection
Thermal regulation
DIP7 housing

4 Applications

LED ceiling light
LED bulb lighting
Other types of LED lighting

U1 circuit is BP2525

This is a simple device. After uploading the batch, it should be possible to discover the pin configurations (which PWM is used) by:
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