Analysis of ASUS NV chipset motherboard auto power off

At present, a large number of ASUS m2n68, m4n68, m5n78 waiting for NV chipset motherboards are repaired in the market. When only the atx20 pin power supply is plugged in, the power supply is normal, and then the 12vcpu VCC power supply auto power off Current protection is plugged in. Most of these failures think that Current protection is caused by Short circuit of CPU VCC, which is a detection function of the rear bridge of CPU VCC in NV motherboard,If a good power signal is detected,auto power off Current protection will be carried out.

There are three main reasons for the common NV chipset motherboard auto power off

1.switch signal is abnormal.2. The main board VCC is abnormal.3. The temperature control circuit is abnormal.

At present, there are 1 or 2 reasons for the maintenance of ASUS auto power off motherboard on the market.Switch was used to distinguish the needle.If you plug in the small 12V,auto power off is the second fault.Whether plug in 12V or not,auto power off is the first type of fault, and there are many faults.For NV chipset auto power off, common maintenance methods are as follows.

The first kind of troubleshooting is relatively simple. When the mainboard is powered on, measure whether Switch pin VCC and power on request signal pwrbtn ා are 3.3V. If VCC is low, directly replace the pull-up 8.2k resistor and Io.If VCC is not low, replace IO and bridge.

The second fault is that the bridge detects that VCC is abnormal, and Current protection is powered off.Find and summarize the good signal of VCC during maintenance, remove the bus power supply good signaltriodeThe PG signal was forced to be high, so that the bridge mistakenly thought that VCC was normal and not auto power off.

How to operate: find HT_VLD signal conversion transistor, this transistor in ASUS motherboard is common in the 32.768 Crystal side.Remove the triode, measure whether the signal is high level and whether auto power off.If the level is still low after removal, and auto power off is generally an 8.2k side pull resistance and Bridge problems (common resistance Open,diode value becomes larger).If the high-level 3.3V auto power off is removed, please re measure each VCC of the motherboard one by one. If the VCC is not correct, repair the VCC.

This method has killed a large number of ASUS NV chipset motherboards. I hope the majority of students can be inspired and have a second kill plan for Asus auto power off motherboard.

Triode position.