Clocks

In this page we cover mechanical, electrical, electromechanical and electronic clocks, outlining the repair options

Summary

With the march of technology, many different types of clock have appeared, and with them, differing possibilities and options for repair, whar are outlined here. Some are cherished items for which repair is sought for nostalgic reasons whereas others may be mass-produced with very limited repair options. Restoration and repair of vintage wind-up clocks is a highly skilled craft but even for these a service clean may be within the capability of any careful fixer.

The history and principles of operation of the many types of clock is a fascinating subject. See Clocks - Basic Principles for an outline, which will underpin much of the content of this page.

Safety

Old mains-driven clocks often have poor insulation and without an earth connection to the metal frame. This makes them potentially lethal and a fire risk.

Should you be tempted to try dismantling and repairing a wind-up clock, treat the spring with the utmost respect. It can be very dangerous if released suddenly. If the coiled metal spring escapes from its housing it can instantly turn into a flying snake knife capable of removing fingers and eyes.

Wind-up clocks

These are purely mechanical and are the oldest type of clock still in common use. After many years of service they often stop working because of thickening of lubricating oil and its contamination by dirt, or wear in the bearings and gears. Cheap clocks often fail much sooner, although many cheap early (1860s) American clocks are still going with minimal maintenance despite extensive wear.

Fault-finding and repair

Clock conservation, repair and restoration are highly skilled operations requiring a fully equipped workshop, but a service clean of a simple clock such as a carriage clock is no harder than smartphone repair. A striking clock or cuckoo clock would harder but only as being significantly more complicated.

Before starting work on any wind-up clock it's essential that you unwind the spring in a controlled manner as its uncontrolled release can cause serious injury. Release the ratchet whilst holding the spring tension with the winder. Allow the spring to unwind by half a turn at a time, or only as much as the rotation of your wrist will allow.

As with all types of clock with brass bearings and gears, you must only use special clock oil. This leaves no residue as it gradually evaporates, has sufficient surface tension to remain within a bearing, and does not disolve any lacquer that might be applied to the brass.

Following disassembly you can clean all parts with special clock-cleaning fluid, preferably ammonia-free, and using a nylon brush.

An excellent introduction to clock servicing would be a reasonable quality carriage clock that has stopped working. A blog posting at the Braintree Clock Repairs website takes you step by step through the dismantling, cleaning and reassembly.

A vintage clock containing a fusee is best left to an expert as the failure of the chain, wire or cord can be dangerous. Likewise, replacing a main spring is a hazardous operation, not to be undertaked by the inexperienced.

Should you get hooked on clock repair the British Horological Institute offer a range of in-person and distance learning courses. Lesson One of their Technician Grade course is freely available online - well worth taking a look! Another excellent source of information and advice is from the Forums at the (American) National Association of Watch and Clock Collectors (NAWCC) website.

Electrically-assisted clocks

These have a pendulum or a balance wheel like a clockwork clock, but it's kept in motion electrically rather than by a spring or weight.

A fascinating very early example is the earth-driven clock, invented in 1911 by Percival Arthur Benson. Two different metal stakes driven into the ground served as a primitive battery, delivering just a volt or so. This fed an electomagnet which applied a tiny force to a permanent magnet attached to the pendulum. As the pendulam swung back and forth it operated a set of contacts which reversed the direction of the current, so keeping the pendulam in motion.

Fault-finding and repair

In the case of a vintage mains driven clock the insulation and earthing are likely pose serious safety concerns, which must be addressed before going any further.

The first challenge will be to work out how it operates. A common method would be using a transistor to amplify and reinforce a current induced in a coil by a magnet attached to the movement. The transistor could be a germanium type, less reliable and robust than more modern silicon transistors. You can test it quite easily with a multimeter. If you unsolder it, apply a pair of pliers to each lead to act as a heat sink as you apply the iron.

Mains synchronous clocks

These were very popular as accurate mantlepiece and wall clocks before the advent of quartz movements. A synchronous motor rotates at the mains frequency and a gear chain reduces this to drive the second, minute and hour hands.

Fault-finding and repair

First of all, it must be said that there may be serious safety issues with these clocks. For a start, the insulation is likely to be in a poor state, and to make matters worse, they have exposed metal parts and rarely have an earth connection. This means there is a significant risk of electrocution and possibly also of fire. Electrically they will usually fail a PAT test as they are neither Class I or Class II - they are ‘Class 0’. However, this doesn't mean they can't be repaired or restored.

Often, you will find the coil in the motor is open circuit or burnt out (or both). This coil is driven directly by the mains and creates the oscillating magnetic field which turns the motor spindle. Whilst it may be possible to rewind it, it's likely to have many thousands of turns and the wire will be so thin that you'd be unlikely to complete the task without it breaking.

A good alternative is to rewind the coil with fewer turns of somewhat thicker wire and drive it from a low voltage transformer, ideally an AC wall cube type. This has the added benefit of eliminating the risk of electric shock and greatly reducing the fire risk. How to do this is covered in detail at sound.whsites.net/clocks/ocm.html.

Quartz clocks

These rely on the vibrations of a crystal of quartz for their time keeping, rather than a balance wheel or pendulum.

Fault-finding and repair

Sometimes the setting buttons become unreliable. If they are the standard miniature tactile type you may be able to replace them, but often they just consist of a rubber button with a conductive layer underneath which makes the contact between adjacent circuit board traces. You may be able to improve it by cleaning the contacts or by rubbing a 2B (or softer) pencil on the conductive layer, or applying conductive paint such as Bare Conductive. Yet another type of button consists of a piece of domed metal which clicks like the safety button on the lid of a glass jar to make contact with a circuit board trace.

As with many battery operated devices, dead batteries may leak and corrode the contacts, which will need thoroughly cleaning.

If you remove the hands (these just pull off), refit them both precisely on the 12 so that the hour hand will always point at an hour when the minute hand reaches 12.

Quartz Watches

These run off a coin cell which typically lasts around a year. More modern ones may have a lithium coin cell lasting around 3 years.

Fault-finding and repair

You can save money by changing the battery yourself, but you may need special tools.

The back will be either screw-on or snap on. A screw-on back will have several notches into which you can engage a tool to twist it off. You can screw it back on in the same way. Snap-on backs can be harder both to remove and replace. There will be an indentation at some point around the circumference into which you can insert a knife or removal tool. Considerable force may be required so great care is needed especially if you are using a sharp knife, in case it slips. Replacing it also often requires considerable force. If you can't do it between fingers and thumbs you will need a watch press. This comes with several dies of different sizes designed to apply the force to the watch body rather than the glass, which you would be very likely to smash.

Having got inside you will probably have to loosen a very small screw in order swing a contact out of the way so as to remove and replace the battery. Only loosen it as much as you need to as it will be fiddly to replace if it comes right out.

You may be able to clean up the battery contacts if they are corroded, and provided the leaking electrolyte which caused the corrosion hasn't caused any other damage. Any other faults such as water damage may not be feasible to repair.

Radio-controlled clocks

These generally have a quartz clock mechanism for back-up timekeeping, but get an accurate time reference from a radio signal, such as MSF Rugby, against which they synchronise regularly.

The self-setting mechanism relies on the clock being able to detect when the hands are in the 12:00 position. This relies on holes in the minute and hour gears which line up at 12 o'clock. An LED and photodetector sense this position. Some clocks have a slightly more complicated system allowing the clock to run fast until maybe 11:45 and then more slowly so as not to miss 12:00 precisely, or they maybe able to recognise several positions of the hands, avoiding the need to wind forward to 12 o'clock in every case. All these use the same kind of mechanism, though understanding just how the clock recognises different alignments of the holes may not be easy.

Fault-finding and repair

Sometimes the problem with these is quite simply an unsuitable battery. Make sure it's an alkaline type, not a cheap zinc one and not a rechargeable.

If the clock is still running but failing to synchronise with the radio signal, this is likely to be due to a weak battery. It may well be that the clock mechanism will continue working long after the battery voltage has fallen below the minimum needed by the radio receiver.

The other simple explanation for a clock not setting or resetting itself is just that it may be placed somewhere where the radio signal is inadequate. Try leaving it on a windowsill or at a different angle.

The same problems with push buttons occur as with quartz clocks.

There is probably little you can do about mechanical problems. Should you remove the gears it's likely that they will need to be reassembled in the correct orientation for the setting mechanism to work. If you examine them carefully you may find that the critical ones each have a pin hole which needs to be lined up one with another or with a pin hole in the plastic case. Inserting a pin through these holes during reassembly will ensure the correct orientation. This is likely to correspond to the 12:00 position of the hands.

Flip clocks

These are the earliest widely available form of digital clock. The hours and minutes and possibly the day of the week and day of the month are displayed on flip-down cards.

Fault-finding and repair

See How flip clocks work.

Seven segment display clocks

These may use a quartz crystal, radio signal or the 50Hz mains supply for the time standard.

Fault-finding and repair

Being purely electronic, they suffer only from the same kind of faults as any other electronic device. Push-buttons can become unreliable, and if indiviual segments of the display fail, the problem is likely to be in the connection between the display panel and the circuit board.

External links

• Rod Elliott's Clocks Pages contain a wealth of information on electric and electronic clocks.
• Braintree Clock Repairs have lots of articles about clocks on their website. In particular, see How to repair a carrige clock yourself - the service clean for a detailed guide to dismantling, cleaning, oiling and reassembling a carriage clock, within the capability of anyone with patience and ordinary levels of skill.