Mains powered electric clock repair - Page 1
Forum section: electronics / repair

author: Roman oh
author_rank: Regular Contributor
timestamp: May 16, 2023, 06:12:42 am
content: I am trying to rejuvenate a couple of vintage mains powered electric wall clocks made by Smiths UK. These are 240V 50Hz units, but I guess the principle is the same regardless of voltage. The motors in in each look somewhat different although similar in principle. The coils appear intact in each case (one is 7K, the other about 10K DC resistance) and they draw current when powered (20 and 10mA respectively). No evident signs of corrosion, overheating, or anything lake that around the coils. The spindles spin quite freely by hand, no roughness or binding, but the motors simply won’t start running. The bigger one will start when spun by hand, but interestingly, it will run in either direction equally.Hopefully the photo comes through OK.I have done some googling without too much success, so I thought I might have a bit more luck with this group.Anyone have any ideas?Roman

author: FIXITNOW2003
author_rank: Regular Contributor
timestamp: May 16, 2023, 06:31:47 am
content: see herehttps://sound-au.com/clocks/ocm.html

author: Roman oh
author_rank: Regular Contributor
timestamp: May 16, 2023, 07:13:16 am
content: Thanks,This was one of the first hits I saw… it talks about rewinding clocks to run on low voltage for safety reasons, but doesn’t give me much insight otherwise in to my issue of why these units with nothing obviously wrong with them simply won’t start.I will read it again more carefully, though…Roman

author: wasedadoc
author_rank: Super Contributor
timestamp: May 16, 2023, 05:08:46 pm
content: How old are the clocks? My parents had three different mains powered clocks which would have been purchased after 1950 and I remember them before 1960. I'm reasonably sure they were made by Smiths. It was a feature of the design of all three that they deliberately did not start when power was applied. This was so that if there was a power interruption the clock would remain stopped and thus be obvious that the time was incorrect. All three had a single spindly knob for setting the hands to the correct time. Then you pushed that spring loaded knob briefly to start running. Sometimes more than one push was needed. Two of the clocks had a second hand so it was obvious that they had started. The other was on the mantlepiece so the trick with that one was to put one's ear to the clock face and listen for the motor running. It was extremely quiet so needed no noise in the room.So maybe there is nothing amiss with your motors.Edit: After a bit more memory jogging:1. I think you pushed and held the knob in, then rotated it to move the hands. When you let the knob out the clock was supposed to start.2. I vaguely remember being told that one of the clocks was a wedding present. That would mean it was purchased in 1949. And I was able to tell the time not later than 1956 and don't recall any other previous clocks in the places where those three were.

author: Roman oh
author_rank: Regular Contributor
timestamp: May 17, 2023, 12:42:32 am
content: Thanks, wasedadoc.I’m aware that some of the older Smiths clocks needed a kick start - these are not that old, (more like another couple I have that self start every time) but in any case, the motors are out and i have “kicked’ the living daylights out of them without too much success.RomanAmendment…I had another look at the mechanism and one of them does indeed have a manual kickstart thingummy and a 1951 date stamp. Older than I thought. But it doesn’t start when installed, although the mechanism itself appears quite stiff. Clean up and who knows- at least maybe one is good?

author: Swainster
author_rank: Frequent Contributor
timestamp: May 17, 2023, 02:17:26 am
content: Oh yeah, wow, suddenly that brought back a specific memory of a Smiths clock that my Grandfather had on his mantlepiece. I seem to recall that you had to pull the time adjust knob out and let it spring back to start it off.

author: james_s
author_rank: Super Contributor
timestamp: May 17, 2023, 02:27:36 am
content: There are two problems I've seen with this sort of synchronous motor that stop them from running. One is old gummed up lubrication and another is worn bearings, and I'm using the world "bearing" generously, it's normally nothing more than a hole drilled through the middle that fits over a polished shaft. I did actually have a timer in a clothes dryer once that had an open coil, I rewound it for low voltage and installed a small transformer simply because I didn't have any of the hair thin wire needed to rewind it for 120V and that stuff breaks if you look at it wrong.The ones that always start in the correct direction have a pawl that blocks the rotor from spinning the wrong way around, I've seen that break on one occasion which resulted in a motor that would randomly start in either direction.

author: Roman oh
author_rank: Regular Contributor
timestamp: May 17, 2023, 03:39:33 am
content: So I sloshed the gummy mechanism in solvent for a couple of min uterus, remounted the motor, gave it the required kick start and away it went! Great. Once out of two. But now of course I will need to clean and relubricate it properly.The second is rather more recalcitrant.James, the bearings on the second one are small bronze bushes and they and the shaft mate very smoothly, no detectable slop, rotor spines freely. But the motor won’t start. Unfortunately, the structure is crimped together so any investigation involves de-crimping and possible re-manufacture of little bits, so scope for experimentation is limited.Roman