Sounds to me like you could have a faulty HU6260 chip. I would think this because of the lack of video from the expansion port.
I'd be curious to try tapping the RGB pins or Luma pin from the HU6260 to see if you get any signal.
To test Luma, simply use any RCA cable and run the positive wire to Pin 40 on the HU6260 chip, Then the ground wire to any ground on the Tg16 board. You can plug the RCA cable into composite on your TV. I'd like to know if you get any black and white image doing this. If Luma shows a picture, then you might just have to rebuild the composite circuit using the Turbo Express composite out mod.
You might get lucky and a component or components on the board that amp/mix the composite signal could be bad and it could be repaired or that composite/luma is dead but RGB is still good.
I've worked on quite a few systems where one option of video is still available and can be used that way once wired up appropriately.
Topic: Turbografx 16 graphic glitches? (Read 1303 times)
