Worst Series Retool Ever?

As you can probably tell from my previous posts, I'm quite fascinated by shows that get retooled, especially when the retool happens in the second or third season. When a show gets overhauled late in its run, it's not as interesting, because those are usually done to cope with the departures of key cast members. What I'm talking about is what happens when a relatively new shows changes the cast, the setting, and even the premise. The idea is always that the show has the potential to be a hit, but to do so, it needs to add certain elements that will theoretically make it more appealing.

The thing is, this almost never actually works. The viewers they gain from the new setting or new demographic appeal almost never outweigh the viewers they drive away by changing everything so quickly. It worked with Newhart, but Newhart's retool happened very gradually; the new characters and new setting weren't all introduced in the same episode, and it took over a year for all the changes to be implemented. That helped regular viewers get used to the changes while bringing in new viewers. But when a show starts a new season and the sets are different, the supporting cast is different, the style is different -- I'm not saying it never works, but it certainly has a high probability of disaster.

So what is your nomination for the worst of these retools, either in terms of how bad the changes were, or just how stupid an idea it was to change the show? The classic example, of course, is Mork and Mindy, because as was explained in comments to another post, ABC and Paramount took a huge hit show and retooled it into a much less popular show.

But I think another retool from the same era may be even worse: Buck Rogers in the 25th Century. You'll recall that the first season of this Glen Larson production was the cheesiest thing ever: bad '70s fashions in the future, an annoying robot sidekick (voiced by Mel Blanc, who didn't even bother to make up an actual voice for the character; that was basically just his real voice), and lots of space T&A. But it combined everything people liked in the late '70s and early '80s: cornball humor, action, robots, sci-fi, and jiggle TV. The abbreviated second season had a serious and depressing setting, serious and depressing plots, a serious and depressing supporting cast, and few female guest stars. I'm not saying Buck Rogers was a good show in its first season, though it was better than the second. What I'm saying is that I don't understand the logic: how did anyone think the show would get more popular if they included less humor, action and sex appeal? It would be like retooling Star Trek to make Kirk suicidal and celibate, and replacing every member of the crew with that alien from the Filmation cartoon.