I've been having similar problems with the fuse popping on an old DP treadmill. I've scoured the web looking for a manual, but nothing shows up - which might be because Diversified Products went out of business in 1993 or 1994!

As to the safety key, I could probably send you dimensions or take a mold of mine, but who knows if they're the same from model to model? My model number is 21-3303. Regarding the data unit on top (time, speed, heart rate), mine pulls out of the stand in front and there's a hatch in the back where you put four AA batteries.

Email rskurat@gmail.com for return pics or with information. For those of you who wrote about keys and manuals, are you having fuse problems also? Any advice?

Thx, Ron