CFA634-YFH-KS-CF only backlight, no text/character after running for 1-2 month


New member

Recently i had received a few CFA634-YFH-KS-CF from my customer that claimed no text/characters on the LCD, only backlight available.
It is working fine for 1-2 month before no text/characters can been seen.
Im using serial communication and backlight is power up throught +5V _LED and GND connection.
Can i have some advises before i sending back for RMA?
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CF Tech

The first thing I would check is the contrast setting.

You can use CF_Test:



Use the backlight slider to make sure the module is connected (it should be able to change the backlight brightness) then use the contrast slider to see if you can bring the display to visible.

If that fixes it, set the backlight and contrast to where they look good, then you can send command 9 to save those settings as power-on default.


New member
Hi CFTech,

Thanks for yr advice.
1) I'm able to see the contrast when moved the slider but still no text/characters when tried to input some. i tried to play with some of the cftest setting and found that after restore display 003, i managed to get the text back.

2) I managed to get 2 unit working when input with text. But one of unit the contrast is always darker than the other unit. ( In fact, quite dark, hardly see the text.)
Can i know is there any factory default setting for the contrast and brightness?

3) I still had more LCD module( at least 4 units) coming back to us with the same symptom, no text/characters with only backlight. i juz found out from my customer these problem occur when the LCD module power on/off 5-10 time continuously. My customer claimed they had been doing these test since 2 years ago and had no issues. Only recent batch had so many failures. Pls advice any possible reason for the failure.

Many Thanks!

Best Regards,
USB LCD Displays - Graphic and Character LCDs with a Keypad