Asus A42J boot does not show desktop auto restart repair

Machine model: ASUS A42J

Malfunction: desktop is not displayed when booting,auto restart

Maintenance process: The earliest preliminary judgment is that the graphics card is bad. After all, it is 0809000. However, after careful inspection, it was found that it was not, because no memory was tested, and the I2C bus of the memory had no waveform. Look, the current CPU VCC has been generated, so it was brushed as a BIOS fault. It was not until the pure BIOS bought by TB was found that it was not a BIOS problem.

Asus A42J boot does not show desktop auto restart repair figure 1.

CPU replacement is invalid, so start to study the circuit carefully. This is an old notebook, the bridge of HM55. First, measure the SPI bus with an oscilloscope. If it is found that the waveform repeatedly beats for 2 cycles,auto power off will be automatically generated. It is judged as the program action of EC. Simply put, it is down error code.

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

Find out the diagnostic card, and compare the leads with Boardview.welding is good. Asus’ DEBUG socket lacks a reset signal. Just find a plaorm reset signal around EC, such as PLT_RST, as shown below:

Asus A42J boot does not show desktop auto restart repair figure 2.

Jump wire is ready. You can walk the code when you start it up. After a few error code, it gets stuck. Down error code 14, after consulting some information, there is no exact description. Anyway, my own analysis is down before the memory, specifically, it is the bridge chip except CPU.

Asus A42J boot does not show desktop auto restart repair figure 3.

The chip BD82HM55 was removed from THINKPAD E40, and it turned out to be Blurred screen. Think about bridges that are generally good. It’s just that it’s really difficult to deal with vinyl. Fortunately, there is a microscope. Make up some Solder Mask, and finally REBALLING is on the computer.