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.