Why does my LCD look like a horror movie?

[Richard Lowe]

I've got a strange issue. STM32H757I-EVAL board that is about 3 weeks old. I've been working on a board bring-up for a week and pulling my hair out. So I used an existing project and thinking that maybe I'm not crazy. This is what I see on the LCD ->

[world04]

I am not familar with the 757, but some boards comes with an a SMPS, that needs to be programmed.

it's recomment to cleanup the entire flash by the st-tool and reprogram it by a demo, where u know, that this works. It's possible that the display or the board is defective.

I assume, that the board use the same MIPI DSI Display that ST uses in the Discovery boards. This is connected by a hi density recepticale. Did you have remounted this display?

[Richard Lowe]

I haven't tried remounting, that's a.good idea.

The mipi displays on these boards are amazing, just wish it was easier to understand the ldtc, dsi, dma2, mdma, etc configuration.

Could a poor configuration cause damage?

[S.Ma]

And check the board user manual in case there are different revisions with BOM changes which may make the original demo incompatible.

[Richard Lowe]

It looks like the schematic for the board is incorrect. It has the LCD Backlight pin and LCD Reset pins reversed in the schematic.

[world04]

Hi Richard,

yepp, u are able to damage the display in various ways, but not by just using the timing and init that ST uses in their demos. They are very conservative withe the clock setting.

What i had often in the demos seens is, that they reduces the mpu lock - they not use the maximum availabe speed, reasoned by the limits of the uses memory. Remember, the MPU's memory access is quite fast - often faster as the external DRAM memory.

As an example, i actually uses an stm32F746 Disco, that uses max 200Mhz, but the MPU could run's at 216Mhz.

Just my mind - the display looks anyway defect. The picture you attached, looks strange and i had never seen a display looks like this before - even it's uninitialized.

I had done some experiences with my STM32H747 Disco board because the MPU is the smae Familiy and the display is similar. I wanna see the behavior of them in uninit condition - just power, not more; it's still black until it's initialized by the system.

Check the Connectors and the power of the supply.

[world04]

Well, but the board and display has both worked previosly. Did you had changed the wiring?

The schematic is mybe wrong, but this should not beats the functionality of the shipped board and display.

The source of the isse is mybe find on the displays board. I had seen similar looking display outputs if the negative voltages or supply from ot to the charging pumps failed.

The background illumination is realized by LED and this looks different if they are failed.

The display is smart, mean's, , that a MIPI-DSI Controller controlls the display an then voltages, that the tft panel requires. If i am rembered right, the display is driven by just one voltage (3.3V). If this is available, the display init in default mode, where is save - even it's not initialized. It's should be stayed black if just a powered up, without any digital connection.

If not, the display is death. Why? I,dont know. Replace it by a spare display. I got a new one for around €20.- ($22.-) at ebay.