Apple a1502 laptop screen does not display maintenance

Apple a1502 laptop screen does not display maintenance

Apple a1502 laptop screen does not display, q7700 P channel venue has not been connected, G level has always been 12V, began to measure and chip connected components,diode value are normal, dismantle a same model of comparison found, r7720, r7721,VCC is not normal, decisive change,booting up success.

Machine model: Apple a1502

Fault phenomenon: notebook screen does not display, dark screen

Maintenance process:
The machine has the sound of Apple turning on, and the screen doesn’t show. I think it must be a second kill, but I didn’t take any photos. As a result, I slapped my face.It’s no problem to test the screen with other machines. After dismantling the machine, it was found that the q7701 had water damage trace, and it was replaced directly. I thought that it was finished. The screen connection test still failed. It is suspected that the u7700 is also broken. It is replaced directly, and the fault is still the same. This time, we have to check it carefully.

Apple a1502 laptop screen does not display maintenance Figure 1

Apple a1502 backlight VCC is named ppvout_S0_Lcdbklt, since it is a dark screen,VCC is definitely not available.

Apple a1502 screen does not display the picture of the notebook

VCC 5v and EDP_BKLT_The en backlight EN is normal, and the basic working conditions of the chip are normal. However, the p-channel venue q7700 is not connected, and the g-level is always 12V. According to the working principle of the chip, the VCC 5v is normal, the current detection resistance r7700 detects that the main VCC current of the boost circuit is normal, and the chip pulls down bklt through 11 pin_SD signal, let q7700 turn on, then pass through EDP_BKLT_EN backlight EN, through the I2C series bus to identify the screen information, open the boost.
But the bklt of 11 pin_SD signal is not pulled low, suspected chip itself problems, and replaced another, the fault is still.At the beginning, the components connected to the chip,diode value, were all normal, and no problem was found. After dismantling a set of components of the same model, it was found that r7720, r7721,VCC were abnormal.

Apple a1502 laptop screen does not display maintenance Figure 3

These two signals lead to the backlight interface of the keyboard, but I didn’t expect to affect the screen display.Under normal circumstances, the VCC is 0.2V when connected to the screen, but there is more than 1V in the fault machine. It is determined to change it, and finally it is finished.booting up is successful.