Tandy Zingo is working in MAME, but the shot button is unresponsive sometimes. I can't find any video of it on Youtube. Did you play it before you decapped it? and if so, was the shot button always responsive, or needed to press it multiple times on occasion(as if the button is worn out).

This is the original version btw: http://www.handheldmuseum.com/Misc/AOneArrangeBall.htm
also released by LJN: http://www.handheldmuseum.com/Misc/LJNComputerImpulse.htm