Re: What happened to Data's emotion chip?
It's a few years since I read them, but a bad call by the Enterprise (or something that looks like a bad call until the truth about alien influences emerges) leads to the destruction of another starship and its crew. The Starfleet enquiry into the tragedy comes down hard on Picard and his crew, and one of its decisions is that Data's emotion chip causes him to behave erratically, and that if he wants to stay in Starfleet he'll have to agree to its removal.
That's probably a very rough and ready summary - it has been a few years since reading that series!
"Some days are better than others. They say that where I come from."
"Loudly, I imagine, on the day you left."
(Blake's 7 - Rumours of Death)