LCD Enable Pin (Atari Lynx II)
The LCD detect pin (pin 25) is used to detect when a screen is inserted. The Hayato screen is different than the Mikey (VLSI) screen.
The Mikey (VLSI) screens short pin 25 to ground.
The Hayato LCDs do not.
The Mikey motherboards pull LCD detect to 4V through a diode, and if it is not sunk low to ground it won't show an image on the LCD (its the LCD itself that expects to see a low logic signal on this pin, to turn on).
The Hayato motherboards already have this pin low (0.7V approx) so the LCD by default will always be told to be on.
For this reason, if you connect a Mikey LCD to the Hayato motherboard it will work, but if you connect a Hayato LCD to a Mikey motherboard it will not, as the Mikey motherboard is keeping the LCD Enable pin high.
To fix this and support both screens, just short pin 25 to ground all the time on Mikey motherboards.
Now your Mikey motherboard is compatible with both versions of screen.