The electro-mechanical ('clunk' type):-
This has a solenoid to wind a spring, and a pair of contacts which gradually get closer together as the clock winds down, then when they finally touch, the solenoid is energised with a 'clunk' as it winds the spring up. It does this about every minute or so. The hair-spring balance wheel mechanism is subject to temperature and lubricant viscosity changes, and is not very accurate in practice.
Usually a faulty one has either a melted fusible link or dirty solenoid contacts. See below for repair hints.
Use a multi-meter to see where in the circuit there is a bad contact. If the circuit is good as far as the points, clean the points with a bit of fine glasspaper/sandpaper (preferred), though I don't think any sort of fine abrasive would be a big problem.
Melted Fusible Link
Use the melted solder again as it has the right melting point. I gather from Jim Adney email@example.com that as a battery runs down, there is a point when there is not enough power to quite finish the winding and open the contacts, so it sits there getting hotter, and the link melts. It's a warning not to leave a battery connected in a dying car!
Electronic (transistorised) clocks:-
Generally these are black-faced, but occasionally grey for late '71 models.
They have a transistor and two very fine coils, one green coated wire and the other red. A pendulum swings across the coils. The transistor is biassed to conduct through one coil, which attracts the pendulum by electro-magnetism. This movement induces a back emf in the other coil, which changes the bias on the transistor base to stop it conducting, so the pendulum returns and the cycle repeats. They are better at time-keeping than the others, being correct twice a day (old joke!).
Repairing Electronic (transistorised) clocks
I've had success by spraying the mechanical parts with WD40 - I believe its role is to thin the original lubricant that has become sticky. Don't flush (eg soak in WD40) unless you are convinced the face etc will be unaffected.
This is about the only 'repair' possible. I believe in some cases the very fine wires of the coils get corroded by flux used to solder them to the small circuit board. Unless you have micro-soldering skills, I think it's unlikely you'll make a successful repair to that. In another case the pendulum had rubbed the surface of the coils and worn through.
It is possible with ingenuity and removal of the back-plate to adapt the clock to use a cheap quartz movement. I've done it as a functioning mock-up, while another club member adapted his clock in a similar way and has it running in his Type 3. If the original fault is terminal, I see no objection to such butchery!
Ted Harding's mod for converting the awkward electronic clock with a quartz module is in a .pdf - click here.
It should apply equally to the early 'clunk' model, but they are usually repairable by resoldering the fusible link or cleaning the contacts, so unless you are particularly bothered about it needing daily adjustment, it's probably better not butchered about.
Electro-mechanical Clock Repairs
Up to '71 it's usually the type that goes 'clunk; every minute or so. An electrical solenoid pulls an arm across that winds a spring, then it gradually unwinds until the contacts inside close again.
A white plastic back shows it's that type. There are a few grey faced clocks (pre-'72) with the transistorised mechanism and a metal rear cover but not many, and they often can't be mended. Mostly they are in '72-'73.
Check fuse first! Twist it in the holder. Turn panel lights on - does clock light up? Don't know which fuse the clock is on, but, hey, they may all need a twist to make better contact!
If clock is in dash, reach behind and squeeze spring metal clips together - wiggle one out then squeeze the other clip and wiggle the clock out. Remove the wires (light can come out) and insulate as live all the time.
Remove the back.
Look for where the wiring connects, and for a small pair of electrical contacts. Get some fine sand-paper and clean up contacts. Look for a gap in the wiiring - there's a fuseable link of low melting point solder. It can melt if the battery gets too low a charge to fully wind the clock, allowing the points to stay closed.
If the link is broken, try holding them together with a soldering iron held on for a short time - it may work. If not you'll need to see if you can find a source.
Give it a go - you'll be no worse off if it doesn't work - and at worst you'll have a clock guaranteed to be correct twice a day! the originals need adjusting most journeys, I find!
Electrical trouble shooting; circuit diagram links; component repair
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