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resetting BIOS from motherboard

Discussion in 'General Electronics Discussion' started by zulu, Sep 9, 2015.

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  1. zulu


    Sep 8, 2015
    Hi everybody!
    Trying to fix some problems concerning the main fan of a laptop, I was advised to reset the BIOS. I knew that normally disconnecting the BIOS battery is sufficient to do this task, but I was asked to short a couple of pins for 30 seconds with motherboard off, so without Power supply, laptop battery and BIOS battery.
    Components to short: JOPEN or capacitors C194 and C195 or diode D27 (Cathode and ground or anode and ground). See the following diagram:
    Should I expect with this procedure to reset all the BIOS settings, cancelling even the altered bytes (including data not accessible from the bios menu)?
    And should I get this result with a simple screwdriver and with motherboard completely off, without Power supply and batteries connected?
    Please, someone tell me something about BIOS resetting techniques.
  2. eetech00


    Nov 17, 2014
    Generally, Bios settings are not stored in non-volatile memory. Settings are retained in memory by power from an onboard battery. So removing all power from the system, including the battery, should clear the settings.

    Basically, when you short JOPEN with all power removed, your ensuring that no residual power remains in capacitors that might maintain power to memory, preventing the bios settings from clearing.
    Shorting the capacitors discharges any energy that might be stored in them.
    zulu likes this.
  3. Bluejets


    Oct 5, 2014
    There is a difference between resetting the bios ( to factory defaults) and clearing the bios chip ( as you are attempting).
  4. Gryd3


    Jun 25, 2014
    Clearing the BIOS settings like this leaves the memory responsible for the settings in an unknown state. When you power on the device, the BIOS should recognise the settings are invalid/corrupt and automatically revert to a default. (This may be a 'safe' default, or other preconfigured default.)
    As Bluejets points out, a 'reset' could be attained simply by booting into your bios and looking for an option to reset the settings. This is usually on the last page with the 'save & exit' prompt, or may even be at the bottom of the page with a dedicated keyboard shortcut.

    The only time I would recommend a clear like this is to bypass a BIOS password that may be set preventing you from booting the machine or altering BIOS settings. (This has NO impact on Windows Passwords!)
  5. zulu


    Sep 8, 2015
    And what does clearing the BIOS chip imply? Will the BIOS need to be reprogrammed or will it be sufficient to update it after booting the operating system?
  6. eetech00


    Nov 17, 2014

    Perhaps I should clarify my statements in post #2.

    My reply was based on your use of "BIOS settings" being synonymous with "CMOS settings". The CMOS settings are stored in volitile memory so my statements for that would hold true. But if you are referring to the default settings flashed into the BIOS chip then that is something different. The content of the BIOS chip can't be changed without re-flashing its content. When the "BIOS settings" are cleared, they are really just reset back to the defaults. Normally, when a BIOS update is performed (re-flash the BIOS) it is recommended to select a BIOS menu item "reset to defaults" to completely reset BIOS (which implies there are locations in BIOS that could remain untouched even if re-flashed).
    Last edited: Sep 9, 2015
    Gryd3 and zulu like this.
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