Reset CMOS for MSI B760M Mortar | Generated by AI
Question: How do I remove the BIOS/CMOS battery and drain residual power from an MSI MAG B760M Mortar motherboard, given a PSU that produces a buzzing/whining sound and no display?
Answer:
This is a standard troubleshooting step for a system that won’t POST and has a coil-whine/buzzing sound from the PSU — it usually means the PSU is trying to deliver power but something (VRM, GPU aux power draw, or a bad CMOS state) is causing it to fault or the board isn’t reaching POST. Here’s exactly how to do the CMOS reset + full discharge on the B760M Mortar:
1. Full power down first (critical — this is the “drain” step)
1. Turn off PSU via the physical switch on the back
2. Unplug the PSU from the wall outlet entirely
3. Press and hold the case power button for 10-15 seconds
(this drains capacitors on the motherboard/PSU — this IS the "放电" step)
The power button press with PSU unplugged is what discharges residual capacitance in the board’s power delivery circuits. Without unplugging the wall power, standby voltage (+5VSB) is still live even when the system is “off.”
2. Remove the CMOS battery
On the MAG B760M Mortar, the CMOS battery (CR2032) is located near the bottom-right of the board, below the PCIe slots, next to the SATA ports. Steps:
1. With PSU unplugged and power drained (step 1 done)
2. Locate the round silver coin battery (CR2032)
3. Push the small retention clip next to it — battery pops up
4. Remove it fully
5. Wait 5-10 minutes (your instinct of 5 min is correct)
6. Reinsert with + side facing up (same orientation as before)
3. Alternative: JBAT1 jumper (faster, same effect)
Instead of pulling the battery, MSI boards have a JBAT1 (Clear CMOS) 2-pin jumper near the battery, sometimes with a small “Clear CMOS” label silkscreened on the PCB:
1. PSU unplugged, power drained (step 1)
2. Find JBAT1 pins (check your manual PDF — search "JBAT1" in the B760M Mortar manual)
3. Short the 2 pins with a screwdriver tip for 5-10 seconds
(or use the jumper cap if included, short for 5-10 sec then remove)
This does the exact same thing as pulling the battery — resets CMOS/BIOS settings to factory default — but is faster and doesn’t risk you losing the tiny battery or bending the retention clip.
4. After reassembly
1. Reinsert battery / remove jumper short
2. Reconnect 24-pin ATX + 8-pin CPU EPS power
3. Reconnect PCIe 8-pin/6+2-pin to GPU (you confirmed this is connected — good, that's necessary for GPU to get power beyond the slot's 75W)
4. Plug PSU back into wall, flip PSU switch on
5. Power on — first boot after CMOS clear will say "CMOS checksum error, press F1" or similar → just enter BIOS and load defaults or save & exit
What the buzzing PSU sound most likely means
A “zizizi” (coil whine) on power-on with no display is commonly one of:
- VRM/MOSFET coil whine under load spike — often benign but sometimes indicates the board is drawing power and faulting before POST (common with bad CMOS state, bad RAM seating, or GPU power issue)
- GPU not seated fully in the PCIe slot — reseat it, you should hear/feel a click on the latch
- RAM in wrong slots — B760M Mortar needs specific slots for single-stick boot (usually slot 2, check the silkscreen A2/B2 near CPU)
- PSU itself is failing — if buzzing persists after CMOS reset, RAM reseat, GPU reseat, test with a different PSU if you have one available
Quick diagnostic checklist if the CMOS reset doesn’t fix it
1. Remove GPU, try booting on iGPU (if your CPU has one) via motherboard HDMI/DP
2. If iGPU works → GPU or GPU power cable issue
3. If iGPU also fails → reseat single RAM stick in slot A2, remove all other RAM
4. Check 24-pin and 8-pin CPU power are FULLY seated (common half-inserted issue causing buzzing)
5. Check for the debug LED / debug code display on B760M Mortar — it has a CPU/DRAM/VGA/BOOT LED sequence, tells you exactly which stage is failing
The debug LEDs (CPU, DRAM, VGA, BOOT) near the 24-pin connector are your best diagnostic tool here — check which one stays lit when you power on, that tells you exactly where it’s failing rather than guessing from the buzzing sound alone.