I had countless great days with the TurboGrafx and Duo, but the best I can remember is Christmas morning when I opened up my Duo. I knew I was getting it (found it hidden prior to Christmas), but the thrill was still huge when I ripped off the wrapping paper.
The thrill quickly turned to disappointment, however, after I hooked it up to my Grandmother's TV and saw no picture. You see, this was back in the day when AV cables were relatively new. All my prior consoles and VCRs had used coaxial cables. So when I hooked up the Duo and placed the 3-in-1 disc into the tray I expected to pop the TV on channel 3 or 4 and do some gaming. But no luck. I pushed buttons, jiggled cords, yet nothing happened. After my Mom and I messed around with it for a good twenty minutes, we figured the machine was defective and would have to be returned.
Completely disappointed, I sulked on the couch for a while with the TV remote in my hand. Staring at it, I saw a button marked "Video Input". Curious, I went back to the TV, turned on the Duo, pushed this mysterious button, and BAM: GATE...OF...THUNDER!
Best day of gaming EVER!