STM32H747i-Disco board (LCD Display Problem)

[vanisrinivasulu]

I am using the STM32H747-I Discovery Board. When I connect the CN2 power supply to the board, it turns on, and LED5 lights up green, indicating the board is powered. However, the LCD display does not turn on. I tried enabling the backlight by setting the BL_CTRL (PJ12) pin high, but it did not work.

Previously, I raised this issue, and an ST employee provided debugging steps, as follows:

1. Step 1: Check if the "+5V" power supply is provided correctly. Probe either C3 or C76 on the MB1248 board.

2. Step 2: If step 1 confirms that 5V is provided well on the MB1248, check if the LCD board (MB1166) is receiving the 5V. Probe C3, C4, or C5 on the MB1166 board.

3. Step 3: If step 2 confirms that 5V is supplied to the LCD board, check if the output voltage is correct. Probe C1 or C2 on the MB1166 board. You can also measure Vfb by probing R3 on the MB1166 board.

The issue is that some of these capacitors and components are located underneath the display, making it difficult to probe them.

Can you clarify:

1. Does providing a 5V power supply alone ensure that the backlight turns on? Or are there additional steps (such as setting PJ12) required to enable the backlight?
2. How can I check the capacitors and components located under the display? Is there an alternative debugging method or tool to verify these points without removing the display?

Best regards,

Vani

[CYANG.1]

Hi,

1. The 5V from main board can not guarantee the working of backlight. the 5V is boosted to around 25V to power the backlight through a boost circuit on the LCD board. So it is better to ensure 5V on C3/C4/C5 or TP5 and around 25V on C1/C2.

You may check if R4 is mounted on the LCD board. if not, BL_CTRL is useless, you don't need to care about this signal.

2.Normally we solder a wire on the capacitor and the wire can extend out of the board, so we can measure the voltage through this wire.

3. Firstly, it is better to confirm flexible cable of LCD is well connected into CN2 on the bottom side of LCD board.

B.R.

[liaifat85]

The LCD backlight on the STM32H747-I Discovery Board requires both a proper 5V power supply and the correct control signals to operate. Providing a 5V power supply alone does not guarantee that the backlight will turn on. Control signal (BL_CTRL on PJ12) is used to enable or disable the backlight, and it must be set high. If you have a logic level analyzer or oscilloscope, you can check the state of BL_CTRL pin. 

If you think about designing a DISCO board of yourself, you may take a look here:

https://www.pcbway.com/project/shareproject/Oberon_STM32F429I_DISCO_station_af64426e.html

[Tesla DeLorean]

Did the display work when you first used it?

Did you save the Internal Flash content before overwriting it with your own code?

Bringing the display up to a point you have images painted on it is quite involved, not just application of power to the STM32H747

Build one of the demos, or reload original applications, use those to check the display remains functional, and then debug your own code.

https://www.st.com/resource/en/compiled_demos/stm32h747i-disco_demo.zip