Cmos power-down circuit failure _ CMOS circuit common troubleshooting

**Pay Attention to the CMOS Power-Down Problem:** (1) When replacing the motherboard battery, it's crucial to use a high-quality battery. Poor-quality batteries may lose power after just a few months, leading to a CMOS power-down issue. If the new battery is of good quality and hasn’t been used for long, yet the CMOS still fails, there might be an issue with the motherboard’s circuitry. In such cases, it’s recommended to have the board inspected by a professional. (2) Before replacing the battery, always check the old one for any signs of leakage. If there is leakage, clean the area thoroughly to prevent further damage to the motherboard. If this is a new system, consider not only the battery but also potential issues with the motherboard or other hardware components. It’s best to contact the computer vendor for assistance in such situations. (3) If you’re trying to fix the CMOS power issue yourself, start by checking the resistance or diode in the battery circuit on the motherboard. Look for any leaking capacitors or improper jumper settings. If there’s a problem with the integrated circuits, it’s better to seek help from the manufacturer or a qualified technician. As an alternative, you can connect an external 6V battery or a battery box with 2–4 AA batteries to the motherboard’s external battery connector. Be sure to follow the polarity indicated on the motherboard manual. For added safety, you can add a 51Ω resistor in series with the positive terminal. These external batteries are available at computer stores or electronics shops and can provide long-term power if used properly. **Common Troubleshooting Methods for CMOS Circuits** **Common Faults on the Motherboard CMOS Circuit:** 1. **"CMOS checksum error – defaults loaded" appears during startup.** **Fault Analysis:** This message indicates that the CMOS data is corrupted or not being saved properly. Usually, this happens when the battery voltage drops too low. If the CMOS power circuit is functioning correctly, replacing the battery should resolve the issue. **Solution:** Replace the motherboard battery if the CMOS power circuit is in good condition. 2. **The "CMOS checksum error – defaults loaded" error reappears even after replacing the battery.** **Fault Analysis:** This could be due to a faulty power diode in the CMOS circuit or increased resistance between the diode and the jumper. A leaking filter capacitor can also cause this issue, as it drains the battery voltage over time. **Solution:** Test the diode and filter capacitor. If they are faulty, replace them. If they are working, check the resistance value between the diode and the jumper. If it’s higher than expected, replace the resistor with the same value. 3. **CMOS parameters are lost. The system displays “CMOS Battery State Low” and sometimes crashes after booting.** **Fault Analysis:** This usually points to insufficient CMOS power supply, which can result from a weak battery or leaking capacitors in the CMOS circuit. **Solution:** Replace the battery first. If the issue persists, check for capacitor leaks. If the capacitors are damaged, replace them. Also, inspect the battery socket for looseness or damage to the power diode or transistor. 4. **System time is incorrect and cannot be saved after resetting.** **Fault Analysis:** This is often caused by a damaged crystal oscillator in the real-time clock (RTC) circuit. **Solution:** Check the crystal oscillator for damage. If it’s faulty, replace it. If the crystal is fine, check the adjacent resonant capacitor for damage. 5. **After replacing the battery, the system won’t boot.** **Fault Analysis:** Even though the battery was replaced, the system failed to power on. This could happen if the motherboard had residual current during replacement, potentially damaging components like diodes or capacitors. Further testing revealed that the south bridge chip was damaged. **Solution:** Replace the south bridge chip with a compatible one from the same model motherboard. **What to Do When You See "CMOS Battery Low"?** The CMOS is a small RAM chip on the motherboard that stores BIOS settings. Sometimes, the system will show a warning like “CMOS Battery Low” or “CMOS Memory Size Wrong.” This doesn’t always mean the battery is dead. Here are some steps to troubleshoot: 1. **Replace the battery and clean the motherboard.** Start by replacing the battery and cleaning the board to ensure no corrosion or debris is affecting the circuit. 2. **Check the CMOS Clear Jumper.** Some motherboards have a jumper labeled “Clear CMOS.” If it’s set to “Clear,” change it back to “Normal.” 3. **Ensure the CMOS Clear Jumper is properly connected.** If the jumper has fallen off, it may constantly reset the CMOS. Reattach or replace it as needed. 4. **Consider motherboard issues.** If none of the above steps work, the problem might be with the motherboard itself. In that case, it’s best to send it for repair or consider replacing it with a new one.

2.54mm Pitch

2.54mm Pitch

2.54mm Pitch

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