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Mango clock resetting to Jan 2000 - bad backup battery?


  • We have recently had 2 fairly new MangoeES's whose hardware clock and system time have reverted to Jan 2000 after they have been unplugged for a day or two. We are planning to try replacement of the button cell battery that presumably powers the hardware clock when power is disconnected. Maybe we have a batch with a bad batch of backup batteries? Any thoughts?


  • Hmm, it does sound like a battery issue, but it could also be that the hardware clock wasn't set somehow and for some reason in the normal course of production. You can try running, sudo hwclock -w after you've noticed date is producing the right output (so connect it to the internet and let ntp do its thing first). This would write to the hardware clock. If after you've observed that a hwclock -r produced the right date prior to a power cycle but not after, then it would surely be a battery issue. If however it retains time, it could have been an issue during the production of the units or it could be the batteries lost contact in transport, or something to that effect.


  • Thanks Philip
    I should have mentioned that I did use hwclock -w to set the hardware clock. A power disconnect of a couple of days has then lost the date. We will try new batteries. Do you have some idea of how long the backup batteries should last? I expect the total time disconnected from power is the most important measure. I would have thought it would be a couple of years?


  • Yes, it should be a couple years, and that would be with the unit powered off the whole time such that the battery was sustaining the clock. It's possible perhaps that in the journey from the factory to its current moment that the battery was dislodged by a firm smack or drop.


  • Hi Philip

    I'm back from 4 weeks holiday and following up on this. It occurred with several mangoes in a box of 10, so unlikely to be battery dislodgement. I have powered up a few mangoes that have been sitting around a while to reproduce the issue, but so far they have all held their date/time. Have you had any other reports of mangoes losing their date/time?

    Andrew


  • Welcome back Andrew! All instances I can recall of instances losing their set times have been battery issues, and could possibly have been that the hwclock -w command was never run, which could be the case if ntp servers were not available at the time of manufacture and when you checked it first. Unless these are particularly old, there should be a primitive script to avoid this issue at /opt/control/saveRTC.sh

    It does seem unlikely to be the battery losing contact for some period during shipping, but it is possible.