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Old 07-01-2022, 07:25 AM   #1
SluggerB
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Default Digital desk clock runs fast

I picked up an old school Timex T121 desk clock from a garage sale. It runs fast, it picks up about a minute or 2 minutes a week.

I wanted to see if there was some sort of crystal or something I could replace that would correct that. I opened it up, however I don't see any type of crystal on the board, although truth be told I am not sure what I am looking for. The only thing that looks like a crystal is a small silver cylindrical component, but that is on the LCD board, not the main board, so I don't think that has anything to do with keeping the time.

I know some old digital clocks ran off counting the signal of your mains voltage vs using a crystal, how can I tell if this is that sort of clock and if so can it be adjusted? And from my understanding those types of clocks there only are off a few seconds a month.

Pics of both sides of the main board and the back side of the LCD board (still in the housing)
Attached Images
File Type: jpg IMG-20220701-092149.jpg (357.0 KB, 20 views)
File Type: jpg IMG-20220701-092140.jpg (348.9 KB, 19 views)
File Type: jpg IMG-20220701-092130.jpg (479.6 KB, 19 views)

Last edited by Per Hansson; 07-01-2022 at 11:22 AM.. Reason: Offsite images uploaded
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Old 07-01-2022, 09:02 AM   #2
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Default Re: Digital desk clock runs fast

does the metal cylinder say 32.768 on it?
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Old 07-01-2022, 10:46 AM   #3
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Default Re: Digital desk clock runs fast

I can't see much pics are thumbnails?
I find the crystal tuning is done wrong and they run fast, these 3V clocks. The loading caps are important and how fast they run changes with battery voltage too, I think it's worse with older batteries.
Probably a tuning fork crystal 32.768kHz can be pulled and swapped out.
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Old 07-01-2022, 11:22 AM   #4
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Default Re: Digital desk clock runs fast

I uploaded the pictures here, now they are big instead of a 100 pixel thumbnail!
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Old 07-01-2022, 01:14 PM   #5
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Default Re: Digital desk clock runs fast

Ahh much better pics But this is mains powered? I would check the electrolytic capacitors, I have seen alarm clocks run fast counting extra pulses due to noisy DC power from old caps.
The other side of the board with the crystal, would have to see a pic for what tuning caps if any are there.
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Old 07-02-2022, 05:55 AM   #6
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Default Re: Digital desk clock runs fast

Quote:
Originally Posted by redwire View Post
Ahh much better pics But this is mains powered? I would check the electrolytic capacitors, I have seen alarm clocks run fast counting extra pulses due to noisy DC power from old caps.
The other side of the board with the crystal, would have to see a pic for what tuning caps if any are there.
I checked the caps, they are all fine

Quote:
does the metal cylinder say 32.768 on it?
No marking at all unfortunately.

One thing I realized, the internet tells me some of these older clocks work off the phase of the mains voltage, I had this plugged into a battery powered UPS, maybe that was throwing that off? I unplugged it and plugged it into a wall outlet and it seems fine so far although its only been a day
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Old 07-02-2022, 10:04 AM   #7
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Default Re: Digital desk clock runs fast

Unless you are going to the battery pack continuously which could explain the situation to why maybe running fast
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Old 07-04-2022, 09:17 AM   #8
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Default Re: Digital desk clock runs fast

The UPS must have been it, ever since it's been plugged into the wall it is keeping accurate time (so far at least)
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Old 07-04-2022, 05:30 PM   #9
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Default Re: Digital desk clock runs fast

Not all UPS have a pure sign wave most of them probably have modify sign wave inverter this might be the issue

I have a clock that is also plugged into a UPS power supply and it also runs a minute faster but does not seem to run faster than this over time however if this clock does not see power from the outlet it runs slow and the longer it off line the slower it runs and this is with a fresh 9 volt battery

Last edited by sam_sam_sam; 07-04-2022 at 05:35 PM..
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Old 07-04-2022, 07:48 PM   #10
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Default Re: Digital desk clock runs fast

Only makes sense if the UPS detects a problem and turns the inverter on. Other than that it kicks in the AVR a first. My guess is the power supply.
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Old 07-07-2022, 08:22 AM   #11
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Default Re: Digital desk clock runs fast

Still keeping accurate time when plugged into the wall, so must have been the UPS impacting the sine wave.
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Old 07-07-2022, 05:53 PM   #12
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Default Re: Digital desk clock runs fast

Well that’s the thing… a normal ups is in bypass mode during normal operation. All there is for protection are a bunch of MOV’s.
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Old 07-08-2022, 04:00 PM   #13
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Default Re: Digital desk clock runs fast

Quote:
Originally Posted by SluggerB View Post
Still keeping accurate time when plugged into the wall, so must have been the UPS impacting the sine wave.
Could you please post a picture of the UPS that you are talking about the date plate would be helpful thanks

I live in area that especially in the summertime in past years it would go to battery back at least a dozen times a day and sometimes more often than this but this has improved in the last couple of years and it not as much of a problem as it use to be

I would buy cheaper ups battery backup that did not have line conditioning and I had several devices go bad from this of ups so if have expensive equipment I look for ups that have line conditioning and I have had better experiences

Last edited by sam_sam_sam; 07-08-2022 at 04:10 PM..
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