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Problem with PC clock: keeps resetting itself to a date and time 17 days 14 hours 46 minutes ago. If I manually correct the clock, it stays correct for anything between a few seconds and 3 minutes and then resets itself. It always resets backwards by the same amount, not to a particular constant date (such as 1 January 2005). In other words, when the true date/time was 13:00 on 04/08/2016 (British Summer Time) it would reset to 22:14 on 17/07/2016, and when the true date/time was 18:10 on 04/08/2016 it would reset to 03:24 on 18/07/2016. The resetting happens only when the PC is switched on and connected to the internet. My time zone is ITC + 00:00 (UK) and I’m on Windows 7. Tried so far:

  • If I power off the PC when it is showing the correct time and then turn it on again it still shows the correct time. It resets to the wrong time after an interval of anything between a few seconds and 3 minutes. That seems to eliminate the possibility of a dead CMOS battery.
  • The error is not a whole number of hours (or half hours) away from correct the correct time. That seems to eliminate having slipped into the wrong time zone (and in any case would not explain the 17 days part of the error).
  • My clock settings are set to synch on the net (once a week). If I go into control panel and click “Update now” when the clock is wrong, it is immediately corrected – but again resets itself to the wrong time after an interval of anything between a few seconds and 3 minutes. I have switched from time.windows.com to time.nist.gov and back again, and that makes no difference.
  • Correct time is maintained when the PC is switched on if (a) the router is switched off or (b) the router is kept on but its telephone connection is unplugged. That seems to point to something external triggering a reset every few minutes.

UPDATE: The behaviour described above has lasted all day (past 9 hours+) and was absolutely consistent in the error introduced, but has just changed before I uploaded this question. For the past half hour it has been consistently subtracting just 12 hours (instead of 17 days 14 hours …) from the correct date and time. It is now showing 06:54 instead of 18:54. It still makes the change at some random interval up to 3 minutes after being corrected.

Any bright ideas?

UPDATE/POSTSCRIPT a week later. Without (knowingly) any input from me, the problem ceased, and has not recurred. The clock stopped resetting itself late that evening. Since then I have not replaced the battery, not re-set the time zone, or anything on the PC, nor done anything to the router. I remain completely mystified.

I have, however, today scoured through Windows System event logs, and this is what I found. The problem began, shortly after I logged on in the morning of 4 August, with this event (Kernel-General): "The system time has changed to ‎2016‎-‎07‎-‎17T16:35:43.949000000Z from ‎2016‎-‎08‎-‎04T07:20:30.407398600Z." The log reveals no clue what caused the change. Throughout that day, there were many similar logs, me correcting the date/time and something else shifting it back again. I have discovered that a similar log entry occurs during normal running, about every 10 minutes all day, throughout the time the PC is switched on. Usually the "change" is a fraction of a second; if it's the first of the day it may be a whole second. Except for 4 August, when I fought an invisible adversary who was determined to drag us 17+ days into the past!

Many thanks to all for your helpful ideas – even though, in the event, none seemed to provide the explanation/solution. If the problem recurs I’ll follow up GuitarPicker’s suggestion of diagnostic tools. Meanwhile, I thought it might be useful to provide this update, just in case anyone else has the same problem in future, or if anyone feels sufficiently intrigued or motivated to explore the mystery further.

  • Have you checked your ntp service? – Maxim Aug 4 '16 at 18:15
  • whow that is some funny stuff going on. Have you checked you CMOS time? Does your router cache the time server? Have other machines in your house a developed a recent interest in time travel? What about other people in your neighbourhood using the same isp? – paradoxon Aug 4 '16 at 18:24
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    Is the time on your router set correctly? Does it happen while Windows is booted into safe mode? Have you ensured you're running the latest BIOS version for you motherboard? – Ƭᴇcʜιᴇ007 Aug 4 '16 at 18:32
  • Thanks, all. @ Maxim: I'm not sure I understand this one. I have checked the synch with internet time (time.windows.com) and it works correctly when I click "Update now". But is NTP service something else? – Paul_JHB Aug 4 '16 at 18:55
  • Thanks Paradoxon. All excellent questions! The shown when I go into BIOS setup (that is CMOS time, I think?) is the same as shows on the visible on-screen clock: if the on-screen clock is wrong, so is BIOS; if it's right, so is BIOS. I don't know whether the router caches the time server (not sure how to check that one). The other devices in the house have steadfastly stuck to the correct time - which seems to absolve the router of any blame. Alas, I don't know anyone round here using the same ISP. – Paul_JHB Aug 4 '16 at 19:06
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The external thing that keeps resetting the time is YOU. The computer is just as frustrated as you, wondering why someone keeps setting the time off by 12 hours every time it corrects it.

Check your time zone settings so that you and your computer will agree on what the correct local time should be.

  • Thanks, David. Alway good to look at problems from someone else's (in this case the computer's) point of view! Yes I have checked the time zone setting and it is correct. If the problem had been just 12 hours that would have been the first place to look. But I know of no time zone 17 DAYS 14 hours 46 minutes away! – Paul_JHB Aug 4 '16 at 18:51
  • @Paul_JHB You may be running other software that has its own time zone settings that may let you set any number of seconds of difference. – David Schwartz Aug 4 '16 at 18:52
  • I've not knowingly installed any new software since yesterday, nor did I do anything today to change the 17 days+ difference to a mere 12 hours difference. Nor can I think of any purpose in designing software that would allow 17 days + an odd number of hours and minutes difference. – Paul_JHB Aug 4 '16 at 19:30
  • @Paul_JHB At one time, all time zones had even hour offsets. Then a time zone was added that had a half hour offset, and the assumption of even hour timezone offsets broke. To avoid problems, it's common for software to internally encode (and often specify) the time zone offset as an integer number of seconds. If you punch tm_gmtoff into your favorite search engine, you will see abundant evidence of this. – David Schwartz Aug 4 '16 at 19:33
  • Hmmm. Fascinating stuff, but it doesn't help me to pinpoint any software or external agency that is effecting such an offset. India has been UTC + 05:30 for as long as I can remember. Just looked it up: 1906 for most of India, then the bits that were on other times were brought into line upon independence in 1947. So it's unlikely that computers were designed on the assumption of whole numbers of hours +/- UTC and then along came India (and a few other odd places) causing that to "break". – Paul_JHB Aug 4 '16 at 19:55
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It sounds like the upstream NTP server is wrong or being tinkered with. Typically, your computer will use a domain server if configured, or time.windows.com for standalone machines.

You will need to query your computer's time configuration to see where it is looking for time. From an elevated command prompt, try the following:

w32tm /query /source will show you the time source that it is using. It

w32tm /query /peers will show you a little bit more.

w32tm /monitor will show you the current offset between your computer and the upstream servers. Look for one or more servers that have an incorrect offset (i.e., that agree with the wrong time).

See this related question for more diagnostic tools, such as stripcharts for live monitoring the trend of your clock.

If you want to do a quick reset on a standalone computer, try these instructions from Adrian K's vBlog:

w32tm /config /manualpeerlist:"time.windows.com,0x1" /syncfromflags:manual /reliable:yes /update
w32tm /config /update
net stop w32time && net start w32time

Otherwise, you may need to reset the time settings to the defaults: w32tm /unregister w32tm /register net stop w32time && net start w32time w32tm /config /update

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