Is there any text on the LCD? Sounds like there’s not…
Which console, cable and OSSC input are you using? Even if the LCD is blank, the unit might still work. If you connect something up you can still use remote buttons or hardware buttons to cycle through the inputs.
I had two problems with my construction:
– A resistor in the wrong place (noticed by accident totally by and rectified before first power on of the unit)
– A missing cap. Despite going over the board a few times, I didn’t notice it as I’d added solder to both pads (one of them by mistake) so there was no copper visible. Marqs pointed me in the right direction based on the missing green signal on AV1.
That’s all the basic checks I can suggest (which you’ve probs already tried anyway). Good luck.