Digital desk clock runs fast

**SluggerB** · 07-01-2022, 07:25 AM

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)

**stj** · 07-01-2022, 09:02 AM

does the metal cylinder say 32.768 on it?

**redwire** · 07-01-2022, 10:46 AM

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.

**Per Hansson** · 07-01-2022, 11:22 AM

I uploaded the pictures here, now they are big instead of a 100 pixel thumbnail!

**redwire** · 07-01-2022, 01:14 PM

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.

**SluggerB** · 07-02-2022, 05:55 AM

Quote:

Originally Posted by redwire

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

**sam_sam_sam** · 07-02-2022, 10:04 AM

Unless you are going to the battery pack continuously which could explain the situation to why maybe running fast

**SluggerB** · 07-04-2022, 09:17 AM

The UPS must have been it, ever since it's been plugged into the wall it is keeping accurate time (so far at least)

**sam_sam_sam** · 07-04-2022, 05:30 PM

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

**CapLeaker** · 07-04-2022, 07:48 PM

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.

**SluggerB** · 07-07-2022, 08:22 AM

Still keeping accurate time when plugged into the wall, so must have been the UPS impacting the sine wave.

**CapLeaker** · 07-07-2022, 05:53 PM

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.

**sam_sam_sam** · 07-08-2022, 04:00 PM

Quote:

Originally Posted by SluggerB

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

07-01-2022, 09:02 AM	#2
stj Great Sage 齊天大聖 Join Date: Dec 2009 City & State: Europe My Country: some shithole run by Israeli agents I'm a: Professional Tech Posts: 26,840	Re: Digital desk clock runs fast does the metal cylinder say 32.768 on it?

07-01-2022, 10:46 AM	#3
redwire Badcaps Veteran Join Date: Dec 2010 City & State: Alberta My Country: Canada Posts: 2,627	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.

07-01-2022, 11:22 AM	#4
Per Hansson Super Moderator Join Date: Jul 2005 City & State: ---- My Country: Sweden Line Voltage: 230v 50Hz I'm a: Knowledge Seeker Posts: 5,221	Re: Digital desk clock runs fast I uploaded the pictures here, now they are big instead of a 100 pixel thumbnail! __________________ "The one who says it cannot be done should never interrupt the one who is doing it."

07-01-2022, 01:14 PM	#5
redwire Badcaps Veteran Join Date: Dec 2010 City & State: Alberta My Country: Canada Posts: 2,627	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.

07-02-2022, 10:04 AM	#7
sam_sam_sam Badcaps Veteran Join Date: Jul 2011 City & State: Some times Sunny Jacksonville FL My Country: USA Line Voltage: 120 Volts 60 HZ I'm a: Knowledge Seeker Posts: 3,653	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 __________________ 9 PC LCD Monitor 6 LCD Flat Screen TV 30 Desk Top Switching Power Supply 10 Battery Charger Switching Power Supply for Power Tool 6 18v Lithium Battery Power Boards for Tool Battery Packs 1 XBox 360 Switching Power Supply and M Board 25 Servo Drives 220/460 3 Phase 6 De-soldering Station Switching Power Supply 1 Power Supply 1 Dell Mother Board 15 Computer Power Supply 1 HP Printer Supply & Control Board * lighting finished it * These two repairs where found with a ESR meter...> Temp at 50F then at 90F the ESR reading more than 10% 1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later ) 2 Hem Saw Computer Stack Board All of these had CAPs POOF All of the mosfet that are taken out by bad caps

07-04-2022, 09:17 AM	#8
SluggerB Badcaps Veteran Join Date: Aug 2020 City & State: Philadelphia, PA My Country: US I'm a: Knowledge Seeker Posts: 557	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)

07-04-2022, 05:30 PM	#9
sam_sam_sam Badcaps Veteran Join Date: Jul 2011 City & State: Some times Sunny Jacksonville FL My Country: USA Line Voltage: 120 Volts 60 HZ I'm a: Knowledge Seeker Posts: 3,653	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..

07-04-2022, 07:48 PM	#10
CapLeaker Leaking Member Join Date: Dec 2014 City & State: Atlantic Canada My Country: Canada Line Voltage: Ground, 0Hz I'm a: Hobbyist Tech Posts: 5,218	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.

07-07-2022, 08:22 AM	#11
SluggerB Badcaps Veteran Join Date: Aug 2020 City & State: Philadelphia, PA My Country: US I'm a: Knowledge Seeker Posts: 557	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.

07-07-2022, 05:53 PM	#12
CapLeaker Leaking Member Join Date: Dec 2014 City & State: Atlantic Canada My Country: Canada Line Voltage: Ground, 0Hz I'm a: Hobbyist Tech Posts: 5,218	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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