128x64 OLED Featherwing not working

Trying to interface the Adafruit 128x64 SH1107 OLED with the LoRa Radio Feather. However, even the Adafruit OLED test sketch won’t display anything. Checked libraries, address, serial speed, power, wiring, etc but it still remains dark. Have asked Pimoroni if it might be faulty and awaiting a response. In the meantime, has anyone had similar difficulties? There are only 4 connections: 3V, GND, SDA and SCL so not much to get wrong in the wiring department. Nick