July 20th, 2012 at 8:07 pm (Engineering)
I love fixing things. So imagine my delight when today I finally tore open a wall clock that stopped running years ago and got it working again. This clock has been stopped for so long that I’ve lost the habit of even looking at it, yet I’m so fond of the thing that I haven’t had the heart to replace it. (It was one of the first decorations I added to my first grad school apartment.) I’d previously given up when replacing the battery didn’t do the trick.
This clock has a simple time piece stuck to the back of it. I examined its mount and then carefully pried it off, at which point the hands fell off their spindle and clattered to the bottom of the front of the clock (it has a plastic enclosure). I couldn’t tell if that had destroyed anything, but since I had nothing to lose, I pressed on. I pried the time piece apart so I could get at the inside, which featured a bunch of flimsy plastic gears, a tightly wound spool of copper wire, and a tiny circuit board. I pried this up to see the circuit board, at which point the gears exploded off their mounts and went flying.
Nothing seemed obviously fried or broken with the circuit board, so I decided to try reassembling it. Because I hadn’t taken a picture of their arrangement, I then spent several minutes puzzling out the mechanical logic of the seven (!) interlocking gears (two are underneath in this shot). This is not the correct solution. This is the picture I took after reassembling them the first time (which I thought was correct). Everything fit together, and it started ticking (hooray!), and the little gears all started turning at different rates. But right after taking this picture, when I snapped the case on top, I heard a SNAP and then a little rattle when I moved the case. I was sure I’d broken some vital plastic bit. I opened it back up and found that one of the plastic stand-offs was broken. However, it didn’t seem vital, so I pressed on. The rightmost gear in this shot is the one that’s wrong. I finally figured out that it goes underneath the platform (it’s the gear that lets you manually set the time). The gear that drives the ticking is on the far left.
Encouraged, I snapped the case on, and it was still ticking. I then disassembled the front of the clock to get at the hands. I mounted the time piece to the back of the clock frame, took the battery out (it stopped ticking), stuck the three clock hands on the spindle axis in the correct order, and set them to point at 12:00:00. I twisted the dial to manually set the time, stuck the battery back in, and IT WORKED!
So basically, I didn’t learn anything about what was wrong or how to fix it, except that (as sometimes happens), just taking the thing apart and putting it back together did the trick. The fun part was figuring out how to get in, and then how to fit everything together. It’s possible that some dust had wedged in there or some of the tiny gears were just slightly not touching or the battery leads weren’t making the right contact. I favor the latter hypothesis since I couldn’t hear any ticking. But either way, it works now!