How flip clocks work
Old fashioned digital flip clocks display digits on flip-down leaves. The mechanisms are described in this page.
Summary
The earliest form of digital clock displayed the digits (and possibly days or the week and months), each split into top and bottom halves on adjacent leaves in a pack as in this animation. These are brought into Restart Parties from time to time as cherished legacy items, or treasured finds from a car boot sale or similar. They were electromechanical devices with ingenious mechanisms. An understanding of how they work helps greatly in any repair situation.
Safety
- Old mains powered devices may have worn or perished insulation on the mains lead, creatng a shock or fire hazard. In the oldest devices, the design may be inherently unsafe, for example having exposed metal parts without an earth connection.
The Timepiece
Older clocks normally have a mains-driven synchronous motor, locked to the frequency of the AC mains supply. (The mains frequency is guaranteed to be stable over a 24 hour period, though it may vary slightly over the course of a day). In a very old example, if there are concerns over its electrical safety or if the coil appears to be open circuit, this website describes various options.
If the motor isn't turning even though the coil is definitely not open circuit, then the motor spindle or gears may need cleaning and lubrication. Excessive wear of the bearings may cause the gears to jam, which would be challenging to rectify.
Newer examples may have a standard quartz or radio-controlled timepiece. There are some branded Karlsson or Habitat (probably rebranded Karlsson) clocks where the flip display only displays the date. A conventional analogue time display is driven directly by the quattz movement.
In the case of a quartz or radio controlled movement, first check that the battery is good, and that it is a good quality alkaline type, and not a zinc or rechargeable type. Repair options are limited, and whilst replacements quartz clock movements are readily available online, it may be harder to find one containing the switch to activate the flip mechanism.
The Flip Mechanism
Purely Mechanical
Many flip-clocks have the flip wheels in-line, and like the digits of a mechanical odometer in a car, one complete rotation of each wheel triggers a flip of the next digit. This will take more force than a flip of a single digit, and the most force will be required at midnight when the minutes, hours and day are all changing together.
Such a mechanism is purely mechanical, and any repair will require you to understand what is hindering the correct operation, whether it be a need of cleaning and librication, or he result of wear.
Electromechanical
Karlsson, Habitat and possibly other similar flip clocks have an analogue time display, and separate electro-mechanical flip mechanisms for the day of week, day of month, month and year. These are all driven by separate electic motors and are linked electrically rather than mechanically.