Atari Lynx (1st model) turns on but does nothing

Hi, I have 3 Lynx's. A Lynx I which works perfect, Lynx II also works perfect but the 3rd Lynx has issues.

It switches on (only with a cart inserted) with both batteries and ac adapter but it does nothing.

The backlight turns on and it does the normal click sound but that is it. The game does not load, no sound and you cannot adjust the brightness.

So in a nut shell it turns on including backlight but nothing else. Not even "Insert Game". Nothing.

I tried many games but nothing works.

Anyone know if it is a simple fix ?

It is a Lynx I PAG-0200 Made in Japan