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      Guidance notes for CMOS use and maintenance


      This article offers the guidance notes for CMOS use and maintenance



      The above symptom may occur on the following systems:

      All Idea Laptops

      All Idea Desktops






      CMOS is a device for recording computer BIOS settings information and plays the key role in computer running. Given its unique electrical properties, once cutting off the power of CMOS, BIOS setup information will be totally lost and the computer will be unable to start. This phenomenon, especially, occurs frequently to the computers that have been used for ages. It is mainly caused by the backup battery on the motherboard which has been applied for too long time and only has low voltage. The backup battery should be replaced. However, if CMOS power outage often happens to the machines which have already been replaced with the new batteries, you should consider whether the circuits on the motherboard are faulty. In general use, we must pay attention to the following points:


      1.  During the process of replacing motherboard battery, it is very important to select the recently produced ones with good quality (for example MAXELL CR2032). Otherwise CMOS outage often occurs due to the poor quality of the new battery or because that the battery discharges too much electricity during the long term of storage and runs out all the power in only several months after installed. If the battery has good quality and has not been used for too long, but CMOS encounters power outage, it may be a problem with the circuits on the motherboard. You need to overhaul the boards in a timely manner.


      2. In replacing battery, check if the original battery had leakage. If yes, wipe the leakage off  the motherboard thoroughly to reduce the damage on circuit caused by corrosion. In case of the newly purchased machine, in addition to battery issues, it should take into consideration the motherboard issue and matching problem among motherboard and some certain cards, etc.


      3. If you handle the circuit issue by yourself, you can check whether the relevant battery circuit resistors or diodes on the Board has been damaged, whether the capacitor leaks current and relevant battery jumper settings have problems, etc. If it is verified that integrated circuits on the motherboard has quality issue, external battery can also be applied to resolve this problem by yourself.


      The steps are:

      Attach a 6V laminated battery or a battery holder that can hold 2 to 4 AA cells to the external battery connector of motherboard. Please pay attention to the marks of positive and negative side in your motherboard specification and be sure not to mistaken. For security reasons, you can connect a 50Ω resistor in the battery circuit (positive side) in tandem. The battery connector can be bought in a computer or electronics accessory store. As these batteries are powerful, you can generally use them for a very long time. However, non- leakage and environment-friendly battery should be adopted and put and fix the battery holder to a secure location inside the machine, lest battery leakage damage machine parts.




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      • Alias ID: IG20111008-006
      • Document ID: HT062069
      • Last Updated :26 Mar 2014
      • © 2016 Lenovo