plaahemantha:
Where is the error?
"No working LCD devices" is the error.
That output means the diag tool sees a single pcf8574 chip but was not able to successfully initialize the LCD.
This is usually an issue that the library probed the LCD, but it didn't see the expected signals from the LCD so the diag tool reports that there are no working LCD devices.
Typically that happens if there is a soldering issue between the pcf8574 chip and the LCD.
It could be on the header where the backpack is soldered to the LCD or in a few rare cases a soldering issue of the pcf chip itself to the backpack PCB.
Can you post some clear closeup photos?
I'd like to see the 16 pin solder connections on both sides (the backpack side and the LCD module side)
I'd also like to see a closeup of backpack itself so we can see soldering the pcf chip to the PCB.
--- bill