40x4 Display - Bottom two lines not working

[OHS-awoodbridge]

I have a 40x4 display with an I2C backpack (https://www.surenoo.com/collections/53901795). The chip on backpack is an 8574T. The top two lines work perfectly, but lines 3 and 4 do not work. Do you have any suggestions on where to start troubleshooting?

[dhalbert]

Could you show your code, or at least the initialization?

On that Surenoo, page is it an SLC4004A or SLC4004B? What is the backpack you're using?

[OHS-awoodbridge]

I have the "B" Model with a 4004 IIC Series v3.0 backpack.

The code is your example with the set cursor using the third line. Here is the intialization:
lcd = LCD(I2CPCF8574Interface(board.I2C(), 0x27), num_rows=4, num_cols=40)

[dhalbert]

These 40x4 displays are really two displays in one: two 40x2 displays in one package. There are separate enable lines for two different HD44780 equivalent controllers. This is explained in the README for this library: https://github.com/gshimansky/LiquidCrystal_PCF8574_4004/blob/master/README.md

My library currently does not support this and would need to be modified to add support for the second enable line.

[OHS-awoodbridge]

Thank you for looking in to it.