Inside the Gamegear TV adaptor

I had read somewhere that it was possible to use a Gamegear as display for building a portable NES. That's all the information I had so I tried to find if it was really possible and how to do it.

I knew that a TV cartridge for the gamegear existed. I though, maybe the all the cartridge does is apply the video signal from the tuner to the right contact on the cartridge conector?

I found a file (ggpins.txt) which identified the contact #43 as 'TV cartridge signal'. Unfortunately, when I applied a composite video signal to this contact, it did not work.

Since it was not so simple, I bought a TV cartridge on ebay. After looking inside the cartridge, I think it approximately works like this:

The cartridge pulls contact #43 to ground, taking control of the LCD.
The tuner sends the analogic video signal to a custom chip which displays video on the LCD.

Bottom line, I dont think it's easy to modify a Gamegear to display a TV signal. I created this webpage to inform poeple of my experiments and to allow them to have a look to the TV cartridge circuitry without buying one.

Better buy a second hand TV cartridge or forget about using a Gamegear as display since the image on a Gamegear is not very good: