Asus A42J K42JY does not display automatic restart maintenance when starting

Asus A42J K42JY does not display automatic restart maintenance when starting.

Machine model: ASUS A42J K42JY

Failure phenomenon: startup does not display, and it restarts automatically.

Maintenance process: the earliest preliminary judgment is that the graphics card is broken, after all, it is 0809000. However, after careful inspection, it was found that it was not, because no memory was detected, and the memory I2C bus had no waveform. Seeing that the current CPU power supply has been generated, I brushed a lot of them as BIOS faults, until I found a pure BIOS bought by someone TB, I found that it was not a BIOS problem.

Asus A42J K42JY startup does not display automatic restart maintenance Figure 1

CPU replacement is invalid, so I began to study the circuit carefully. This is an old notebook, the bridge of HM55. First, measure the SPI bus with an oscilloscope, and it is found that the waveform will automatically power off when it repeatedly jumps for 2 cycles. It is judged to be the program action of EC, which is simply the code down.

The LPC_AD0 and LPC_FRAME of the LPC bus are measured with an oscilloscope, and it is found that there is only a few waveform jumps and it stops. Please refer to the above figure for the LPC bus.

Find out the diagnosis card, and weld all the leads according to the point bitmap. Asustek’s DEBUG socket lacks the reset signal, so go to the EC to find a platform reset signal, such as PLT_RST, as shown in the following figure:

Asus A42J K42JY startup does not display automatic restart maintenance Figure 2

When the flying line is ready, you can walk the code when you start it, and it will get stuck after a few codes. Downloading code 14, I looked up some materials and didn’t have an exact description. Anyway, I analyzed it before the memory, specifically, except the CPU, which is the bridge chip.

Asus A42J K42JY startup does not display automatic restart maintenance Figure 3

The bridge chip BD82HM55 was removed from THINKPAD E40, and it turned out to be a flower screen. Considering the bridge, it is generally good. It’s just that the black glue is really difficult to handle, but fortunately there is a microscope. Add some green oil, and finally plant the ball on the machine.