Macbook A1465 2014 Version WiFi Issue
Motherboard No.: 820-3435-A
Malfunction Phenomenon:
When the macbook enters the system, WiFi icon was gray, WiFi function was abnormal.
Possible Reasons:
WiFi module was broken;
The working conditions of WiFi circuit was abnormal.
Troubleshooting:
We removed back cover, disconnected the battery and replaced another WiFi module, then we turned on the macbook and pressed the Option key, WiFi still cannot be recognized.
We disconnected the battery and took out the motherboard, open the bitmap and found out the WiFi connector.
J3501 is the WiFi and BlueTooth module connector, we found out relevant circuit in schematic as bellow.
According to the schematic, the working conditions of WiFi module are as the following shows.
Power:
PP3V3_WLAN, normal voltage value should be around 3.3V, but the value was 0V after we
checked;
PP3V3_S4, normal voltage value should be around 3.3V, the value was 3.3V after we checked,
which was normal;
Clock signal:
PCIE_CLK100M_AP_N and PCIE_CLK100M_AP_P, after U0500 got the clock reuqest singal AP_CLKREQ_L from CPU, they were generated and send to WiFi module.
Reset Signal:
AP_RESET_CONN_L， it’s from the signal AP_RESET_L which was transacted from U3540, the voltage of AP_RESET_L was 3.3V after we checked, it was normal, but the voltage of AP_RESET_CONN_L was 0V, it was abnormal, normal value should be around 3.3V.
Date transfer: We checked the diode value of the data signal without WiFi module.
PCIE_AP_D2R_P was 332,
PCIE_AP_D2R_N was 332,
PCIE_AP_R2D_C_N was 323,
PCIE_AP_R2D_C_P was 323,
PCIE_AP_R2D_N was infinite (diode value was 410 after we assembled WiFi module )
PCIE_AP_R2D_P was infinite (diode value was 410 after we assembled WiFi module )
All the diode values were normal after we checked.
We continued to check the voltage of WIFI_EVENT_L, the value was 3.1V before the screen was truned on, after screen was truned on, the volatge should fall down to 0V, and it should be also 0V if we didn’t insert the WiFi module.
According to the testing process, the voltage of PP3V3_WLAN and the reset signal AP_RESET_CONN_L were abnormal, if PP3V3_WLAN was abnormal, it will make AP_RESET_CONN_L abnormal, so we had to find out the sourcing of PP3V3_WLAN.
After we checked in the schematic, we found that PP3V3_WLAN was from PP3V3_WLAN_R via current detective resistor R5470, so we have to find out the sourcing of PP3V3_WLAN_R.
We traced the rail PP3V3_WLAN_R to the sourcing chip U3550, then we checked the working conditions of this chip.
1. PP3V3_S5 voltage value was 3.3V, normal;
2. Voltage on the enable signal SMC_WIFI_PWR_EN which from SMC was 3.3V, normal.
3. Diode value on PP3V3_WLAN_R was 458, also normal, but the voltage was 0V.
According to the measuring, we could see that the working conditions were normal, but there was no volatge output from the chip U3550, so we can conclude that the chip U3550 was broken.
We replaced another U3550 and checked the PP3V3_WLAN again, it was back to normal value 3.3V, and the reset signal AP_RESET_CONN_L was also back to normal value 3.3V.
We disconnected the power and assembled the parts and tested agian, WiFi was back to normal.
Summary:
One of the power supply for WiFi module was abnormal makes the WiFi can not be turned on, we traced the abnormal rail to chip U3550, we replaced this chip, then the problem was resolved.
