Lenovo m3a760m mainboard is not powered on for repair

Motherboard model: Lenovo m3a760m v1.01

Fault phenomenon: main board no booting

Maintenance process:

A Lenovo m3a760m motherboard, the fault is the motherboard no booting.

Lenovo m3a760m mainboard is not powered on for repair Figure 1.

Lenovo m3a760m mainboard is not powered on for repair Figure 2.

After the power supply is plugged in, the test is that the motherboard does not run out of code. When testing various items of VCC, the first VCC does not exist, and the memory VCC does not.Open schematic to check its conditions.

Lenovo m3a760m mainboard is not powered on for repair Figure 3.

Lenovo m3a760m mainboard is not powered on for repair Figure 4.

Fifth,pin VCC is normal and has 12V, then test EN.

Lenovo m3a760m mainboard is not powered on for repair Figure 5.

The 7th pin is open, a look at the Switch triode directly removed q52.

Lenovo m3a760m mainboard is not powered on for repair Figure 6.

Power on, copy machine test for a day, not booting up.The test still has no memory VCC, which is not a problem with EN.The measured chip conditions are satisfied, and the VCC chip in general memory is the same as the bridge chip.

Lenovo m3a760m mainboard is not powered on for repair Figure 7.

Switch chip, the fault is still the same!Oscillograph test memory VCC under the tube D level actually has instantaneous waveform.

Lenovo m3a760m mainboard is not powered on for repair Figure 8.

Lenovo m3a760m mainboard is not powered on for repair Figure 9.

It can be judged that the upper and lower pipes are defective. Replace the two MOSFET, and the startup test is smooth.booting up is troubleshooting. The maintenance is over.