Trying to See if I Can Fix This Desk Clock - Page 1
Forum section: electronics / general

author: Boris_yo
author_rank: Frequent Contributor
timestamp: October 29, 2022, 02:39:50 pm
content: Hello. The clock's not showing any activity with fresh alkaline batteries. After opening the back cover the cogs don't move. They are supposed to?The coil on top has a wire loose. Don't know if it's supposed to be that way.(Click to enlarge)I don't have any expertise with fixing clocks but I like tinkering with stuff. I wonder which part of the clock failed and whether I can fix it before throwing it away. Thanks.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 29, 2022, 02:45:53 pm
content: Looks like a bunch of gears not meshing.

author: Boris_yo
author_rank: Frequent Contributor
timestamp: October 29, 2022, 02:49:46 pm
content: Quote from: Alex Eisenhut on October 29, 2022, 02:45:53 pmI removed the red cog and the white cog, leaving only the central one. It doesn't move regardless. I thought it's the one responsible for moving the pointers.

author: mariush
author_rank: Super Contributor
timestamp: October 29, 2022, 02:50:24 pm
content: My guess is the coil is an electro-magnet which is turned on every second and moves a metal piece a short distance which in turn rotates a wheel, which then turns the other wheels.If the wire is broken/ loose it's no longer an electromagnet. See what happens when you touch that loose wire to the pad from where it broke off

author: amyk
author_rank: Super Contributor
timestamp: October 30, 2022, 01:48:13 am
content: https://en.wikipedia.org/wiki/Lavet-type_stepping_motor

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 30, 2022, 04:35:29 am
content: Verify that the battery voltage is getting to the clock mechanism. These things are built down to the lowest possible cost and oxide layers on the battery terminals or other similar problems often causes failures in these.Next place to look is at the motor stator itself. Often you will find it twitching, but not turning. Things have worn enough that the proper geometry is not maintained or it is physically rubbing. When this happens I have found a "new" mechanism is the only good solution. I do look at thrift shops for clocks that are either out of style or have water stained faces and find usable mechanisms for far below new prices at domestic sources. Ali Baba will have truly new units for dirt cheap prices.While the physical outline of the movement is well standardized and almost all are interchangeable, the shaft diameters for hour, minute and second hands are not, so either care in acquisition is required or some careful bodging to come up with a workable combination.

author: Boris_yo
author_rank: Frequent Contributor
timestamp: October 30, 2022, 08:58:41 am
content: Quote from: mariush on October 29, 2022, 02:50:24 pmI checked continuity and voltage on different tracks, between 2 pads that have capacitor soldered and 2 pads where each of 2 coil's wires soldered to.(Click to enlarge)I get inconsistent or no continuity between capacitor's pads and capacitor's leads. Voltage fluctuates between tens and hundreds (X.XX and X.XXX) with inserted battery.After checking pads to which coil wires are connected I get good continuity and voltage in hundreds.Also that small cog you see next to a coil is magnetized. I think it is supposed to receive impulses from coil but it does not. I took a small spring and placed it next to coil when it is on metal plate. Battery was connected. But spring didn't move.