This is my recommended method for cleaning the LCD used on the Floppy Emu A and B:
Disengage all the metal tabs, so they’re no longer clipped in place. Gently push the tabs through the holes in the red PCB, until the whole glass and metal LCD module can be separated from the PCB. Set the LCD module aside. On the red PCB you’ll see eight contact points where it meshes with the LCD module. Wipe clean the contact points on the PCB, then replace the LCD module and click the metal tabs back into place.
As others have said, you can also find a replacement "Nokia 5110" LCD on eBay, AliExpress, etc. There are a few different pin arrangements used, so be sure to get a replacement that uses the same arrangement as the LCD you have now. Check the name labels next to the pins.
The OLED used in the Model C is higher resolution and better and contrast with fewer headaches than the LCD. I wish they'd been available earlier so I could have used them in the A/B models.
The check pin message is a self-test failure and isn't a good sign. Make sure you've installed the correct firmware version and you're not trying to run the Apple II firmware while connected to a Mac. Otherwise this probably points to some kind of hardware failure on the Floppy Emu or the computer's disk controller.