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Old 29-04-11, 09:40 PM   #1 (permalink)
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Default why does my old pc keep reverting back to 2003 on start up

Hi folks, just a quick query, as in my old pc keeps going back to the factory time and date, although all my programs etc are still working ok, its not a major issue but it is realy starting to bug me, tried a few times in bios to put the time and date in, but evry time the pc is off for a while it starts with the 2003 date, i use this old pc for all my modem, xbox flashing and im reluctant to get rid of it, any help much appreciated folks, thanks again
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Old 29-04-11, 09:46 PM   #2 (permalink)
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Default Re: why does my old pc keep reverting back to 2003 on start up

would say that the bios battery is goosed
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Old 29-04-11, 09:54 PM   #3 (permalink)
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Default Re: why does my old pc keep reverting back to 2003 on start up

change your bios battery, its not holding the settings when you turn off your pc, its looks like a round silver coin on your motherboard, it just flips out and put a new one in.
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Old 22-08-11, 11:43 PM   #4 (permalink)
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Default Re: why does my old pc keep reverting back to 2003 on start up

be aware if you change your cmos battery as suggested, you may need to leave the pc pluged in, this allows the battery to charge, otherwise you may think the problem is stiill there, using a good battery should fix this.

gl.
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Old 26-08-11, 08:58 AM   #5 (permalink)
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Default Re: why does my old pc keep reverting back to 2003 on start up

Replace the mobo battery is an option.

But according to our experience, sometimes we won't get the problem fixed.

After replacing the battery, if the date still restore back to the manu date, I would suggest just leave the PC as is.

Hope this helps!
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Old 26-08-11, 08:10 PM   #6 (permalink)
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Default Re: why does my old pc keep reverting back to 2003 on start up

Hi Wheeler777 im quite sure the cmos battery is not charge by the pc its just there for backup if you turn off at the plug or power cut i may be wrong.
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Old 26-08-11, 10:14 PM   #7 (permalink)
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Default Re: why does my old pc keep reverting back to 2003 on start up

The battery needs some form of charge, it surely would be given charge when the computer is on or in standby. A new CMOS battery should fix this issue and if it doesn't I would then look at updating the BIOS.
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Old 27-08-11, 12:44 AM   #8 (permalink)
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Default Re: why does my old pc keep reverting back to 2003 on start up

The battery backed RAM is a legacy device designed in long before the popularity of other forms of non-volatile memory (EEprom etc). The RAM devices themselves need a very low power backup supply (around 1/10 Millionth of a single watt of power) for when the main power goies off and this is supplied by a very standard lithium coin cell - the same kind of thing thats used in many portable digital clocks. On average, the batteries will last 6-10 years before replacement is required. These batteries are NOT rechargeable

Note that on some more modern motherboards there is also a power backup capacitor which can be used to hold charge. These charge up instantly on power being applied to the PC and then discharge through the RAM very slowly when no main power is present. They can generally power the RAM for periods of upto 24 hours. This arrangement saves any power being taken from the battery during normal daily use of the PC and can thus greatly extend the battery life.

Last edited by TheCoder; 27-08-11 at 12:48 AM.
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Old 27-08-11, 08:32 PM   #9 (permalink)
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Quote:
Note that on some more modern motherboards there is also a power backup capacitor which can be used to hold charge
Can you provide examples of a mother board desktop or laptop which contains the above mentioned capacitor to hold the charge for the RAM?

very curious to find out about this.

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Old 28-08-11, 01:59 AM   #10 (permalink)
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Default Re: why does my old pc keep reverting back to 2003 on start up

Quote:
Originally Posted by unadkat View Post
Can you provide examples of a mother board desktop or laptop which contains the above mentioned capacitor to hold the charge for the RAM?

very curious to find out about this.
Not specifically although I believe some of the later Gigabyte and Dell branded boards have the very simple modification. Its basically just an extra capacitor and a couple of extra diodes. Probably no more than 2-3 pence in component cost.

The circuit is exceptionally simple, using a diode OR arrangement to select between battery power or capacitor power. Once the capacitor loses charge so its voltage is lower than the battery (battery is usually a CR2032 3V lithium cell type) then the battery takes over

1/ When PC power is on capacitor charges from 5V rail via a diode, so it gets to around 4.4V (0.6V diode drop). A small resistor can be used to limit initial current through the diode if necessary (not needed for a small value capacitor - dependant on RAM current draw and time you require). The diode also serves to prevent the capacitor from attempting to power the 5v rail when the PC power is switched off.

2/ Capacitor and battery are connected together, each through a diode, to the RAM standby voltage pin. The battery will be able to supply around 2.4V though the doide (0.6v diode drop from 3V) so as long as the common point (where capacitor and battery diodes are connected together - the RAM standby voltage pin) stays above 2.4V then the battery diode will be reverse biased - no battery current flows. This will occur whilst the capacitor stays above 3V. With a RAM device that only takes a few nanoWatts of power than can be a significant amount of time !

So, 2 extra diodes and a capacitor and you get yourself hours to days of no power taken from the battery. The value of the capacitor and the standby current requirements of the RAM determine how long you get before the battery is required to take over.
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