[SOLVED] Nokia5110 display backlight is always on?

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kgavionics

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Hello, I bought a few 5110 on eBay, and they're working ok , except they have weird issues. Firstly, in accordance with the data sheet (PDC8544 chip) these displays are 3.3V, but mine they only work with 5v. Secondly, the Backlight is always on whether I hook the pin to 3.3V via a 330 ohm resistor, tie it to the ground or leave it floating, the backlight stays on.
Does someone know what could be the problem?
Thanks in advance
 

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Hi
I have used 5110 modules and didnot face this issue. Some of the modules have an SMD 1k resistor soldered off the shelf. Please check the PCB track of BL pin on backside of module. You might need to solder-out that resistor.

Also I think backlight is due to smd leds on pcb. you might want to carefully remove lcd to see leds soldered on to display board.
 

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    kgavionics

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Thank you for the heads-up
After doing some measurement, I found this how the backlight is wired on my display. (see attached schematic)
 

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