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634 (usb version) serial (no backlight) power up issue


New member
As above. I am having the 634 usb lcd but trying the serial connection (no backlight). The usb, with backlight is working fine. However, when I connect a serial straight-thru cable to the serial port, all I get is a weak backlight and no boot screen. What could be the issue?
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USB LCD Displays - Graphic and Character LCDs with a Keypad

CF Support2

Which model Serial CFA634 are you using?
Even with out a backlight, the module still needs voltage for the LCD itself. If it does have a backlight, you will need to apply your +5v source to J2 -(pin 3, ground is pin 1).


New member
My model is CFA634-YFB-KU. I thought that it would be good enough to plug in the serial cable to achieve display. What I am trying to achieve is to get this LCD to display without backlight on. The problem is that it seems that it does not even boot up.

CF Tech

You have a USB model. Even though the serial connector is loaded, it is no longer fully functional. We do not recommend connecting a serial cable to a USB display -- plus it won't work.

Using USB, you can set the backlight off, and then save that (and whatever is on the LCD) as the boot state. Then the LCD would power up without the backlight.