After frying the coil in my first attempt at repairing my clock, I'm approaching the second attempt with trepidation so I am experimenting on another GM clock with similar internals. I pulled the clock apart, filed and polished the points (they were pitted) cleaned it with electronics cleaner, blew it out, oiled the pivot points, and reassembled it. I powered it with an AC/DC 12v converter that puts out 1,000 milliamps. The clock would not run.

When I bypass the points and touch the power leads to the coil, it actuates (i.e., 'rapidly snaps') and pushes the opposing point, charging the spring, and running the clock for one cycle. This means the electromagnet is likely not the problem.

With the coil-driven electromagnet capable of working, I wondered if the axle holding the opposing point/contact was binding. I again disassembled the unit and more carefully cleaned the openings where those axles rotate on the assembly as well as the axle 'tips' themselves. There was some residual dirt in the openings. After cleaning, reassembly, and power up, the clock ran two cycles and quit.

When I put a multi-meter in line with the power circuit I am only getting about six volts through the clock (I verified the power supply provides 12 volts with no load). I'm wondering if the 1,000 milliamps are not enough to both power the coil AND deal with the system resistance of the clock. (No I am NOT an electrical engineer and have no real idea what I'm doing.)

Worst case, this clock is simply worn out and incapable of running. Best case, one of you experts can tell me the final task I must perform to get it to work. (By the way, based on the advice of others in this Forum I bought an in-line fuse holder in which to install a 1 or 2 amp fuse to avoid further 'coil fries'. If nobody has any better ideas I plan to try powering it with my car battery with this fuse in place.)

By the way, this particular clock was never engineered to have the contacts perfectly align (in other words, stacked and fitted like two perfect pancakes). These points were engineered to join at a slight angle, placing the contact point off center. After looking at this clock, my original, and a replacement coil I bought, it seems to me that these clock contacts were never completely flat. Their faces are slightly arced. So regardless of engineered implementation (even if perfectly aligned and angled), the contact point was much smaller than the face of the contacts. This reduces the need for perfect alignment but places all of the power through a much smaller area. No wonder these things failed so quickly.

 

I can't tell you how the designers wanted the contacts to close. I can theorize that in actually practice, either point contact OR full face contact might be best for the clock....but I don't know the answer.

I agree that I have never seen a contact set that aligned well--which may mean that they were not supposed to do so.

I don't believe that 1000 millamps (1 amp) would be enough power to fire the solenoid. Winding that spring in a matter of milliseconds takes some force. If your power source has a 1 amp limit, you might want to feed it with a car battery to see if it works better (or not).

The mechanical portion of that clock (pivots, etc. especially those involved with the winding action) can take a beating from that "shock" winding from the solenoid. I've see pivots that have eaten into the plates from long-term use. It actually surprised me that they continued working for that long with that amount of damage.

This clock design has some flaws that would not allow it to function over the "long term". So, if you want a working clock and don't want to fix it every few years, go with the quartz movement version that is MUCH more reliable.

 

Thanks '7T1', I pulled the trigger and wired the clock to the car battery. It's running like a champ. I don't understand why, though. I wired a 1 amp fuse in line on the positive wire. Since it can't pull more than 1 amp with that fuse, I'm confused why its running now but wouldn't with the 1 amp AC to DC converter. If you have any ideas, I'm all ears.

BTW, I shut off the power on my car when garaged, so I'm fine with the mechanical clock. I actually like the sound of the ticking when I'm working on the car.

 

I cranked up the clock from my '68 using the AC/DC converter. It is humming along. I wonder why one will run and the other will not.

 

The contact points have to be 'closed' when you put power to it or it will not rewind....and stay dead. And, if the points aren't closed, it means that the mechanism did not run the spring down to where the points would close, thus it has a mechanical fault in the clock.

P.S. I sent you a PM with possible are suppression circuits for the clock.