Huaqing H81M-vg4 REV. 2.01 memory repair

Huaqing h81m-vg4 rev. 2.01 but memory, replace with a good K72 small tube, the voltage is restored to 12V, and the machine is on.

Machine model: Huaqing H81M-vg4 REV. 2.01.

Fault phenomenon: when the light is not on, the PC horn keeps beeping and beeping, and the alarm sounds four times.

Maintenance process: at the beginning, the dirt between the CPU base pin pin was cleaned up, which could be booting up. After using it for several hours, I thought it could be used. I installed it in the chassis another day and found that it was not booting up.After being removed and used several times, the PC horn starts to alarm. It’s not OK to brush BIOS!It’s not good to change CPU!Change memory, memory slot, cleaning slot, or not!Alarm on memory channel ab.SPD VCC, SPD CLK data VCC resistance are OK, and also have waveform, 1.5V memory VCC, VTT VCC, memory reset, all OK, this is strange.

Huaqing h81m-vg4 Rev. 2.01 memory repair Figure 1.
Sit down and do it slowly. Look at the common circuit between the two memory slots on the point

1.Measurement hr99, memory reset,

2.Memory 117, 119 pin are all through the 1K resistor GND of d3r20.

3.CLK is not used and ab channel is not connected.

4.Two 1K resistors d3r5 and d3r6 divide the voltage of VCC and send them to two memory slots for vrefca. The voltage of 0.76v is normal.Finally, look at the memory SPD CLK data circuit, it is found that they are connected to the South Bridge through SQ1 SQ2. These two MOSFET are controlled by pq26. The D pole of pq26 has a 12V pull-up, and the resistance is 8.2k. Test and see, d-pole VCC is 1.26v, which is not correct. Replace the K72 small MOSFET, d-pole 12V appears.SQ1, SQ2 are completely connected, SPD signal enters Nanqiao normally and passes through memory,booting up.

Huaqing h81m-vg4 Rev. 2.01 memory repair Figure 2.

It can be seen from Boardview that 118 pin is connected to S pole of SQ1, its d pole is connected to Nanqiao, and G pole is controlled by pq26.

Huaqing h81m-vg4 Rev. 2.01 memory repair Figure 3.

The measurement of pq26 is a field tube. Its d pole is pulled up to 12V with SR63 8.2k resistance. The actual measurement of d-pole VCC is only 1.xxv, while the g-pole of pq26 is 0V, which is wrong. The measurement of SR63 is 8K ohm, which should be the problem of this small field transistor.
Put on a good K72 small MOSFET,VCC recovered 12V,booting up, maintenance is over!