NHD-7.0-800480EF-ASXN - No Graphics

RAGHUL

• July 14, 2020 10:07

Hi
We are developing a product using Toradex Colibri iMX7 and New haven display NHD-7.0-800480EF-ASXN#-T. We have used a adapter carrier board to adapt the 24bit display with 18 bit RGB lines from SoM. For Back light, we have given externally using a programmable power supply as mentioned in the datasheet limiting the voltage and current to the specified value. It was working fine for 2 days and suddenly it went blank today. Only back light is getting ON and no graphics is displayed. Complete white. But everything was working well for 2 days. We doubt two causes:

1. We probed the PCLK pin. I've attached the images. When the TFT display is connected, the PCLK signal gets dropped.
2. We have pulled up the DISP pin in the display to 3.3V using a 100k Resistor. But only 1.6V is getting into the pin. When used a lesser value resistor, 3.3V is getting into the pin. But that didn't solve the isssue.

Whether this could be the cause? Or any other method to diagnose this issue.

 

Image without display:

Image with Display:

Thank you for your time!

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  Ted M.

  NHD Staff

  • July 14, 2020 11:07

  Hi RAGHUL,
  
  It's possible the voltage levels for the display's 24-bit RGB data and control lines are also borderline.
  The logic levels for a high must be at least 0.7V*VDD or > 2.31V with a 3.3V supply.
  The logic levels for a low must be equal or lower than 0.3V*VDD or < 0.99V with a 3.3V supply.
  Are the logic lines from the SoM able to source enough current to drive the 24-bit RGB data and control lines?
  
  Regards,

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  RAGHUL

  • July 14, 2020 12:07

  Thanks for your quick reply.
  The RGB lines are at 3.3V for logic high and 0V for logic low. Moreover the display was working fine for two days.
  Our main concern is about the PCLK signal. Whether it is supposed to be like that, as shown in the attached image.
  
  Thank You for your time.

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  Ted M.

  NHD Staff

  • July 16, 2020 12:07

  Hi RAGHUL,
  
  Please clarify if you are measuring the DCLK signal input at pin 30 of this display or somewhere else.
  
  Regards,

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  RAGHUL

  • July 17, 2020 12:07

  Yes. It is the 30th pin. And I'm measuring exactly at the end of the display cable.

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  Ted M.

  NHD Staff

  • July 18, 2020 12:07

  Hi RAGHUL,
  
  Please check the DCLK frequency as it should be a minimum of 28.2MHz up to 40MHz max.
  The voltage for the DCLK signal is also too low.  Is it possible there are losses in the line driving the display?
  If the clock source from the MCU cannot supply enough current, it could explain the voltage drop measured with the display connected.
  
  Regards,

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