Laptop Model : Acer A715-71
Motherboard Number : LA-E911P
Fault : Not Charging
Analysis :
When connected to the power
supply, it is not charging. The current is as follows:
Repair Process:
The first step is to open the drawing and find the chip PDF to see if
there are any abnormalities in the pin definition.
According to the drawing above,
we can more intuitively measure whether the chip is damaged.
The measurement results are as
follows:
28-pin VCC: 19V, 6-pin ACDET:
2.6V, 5-pin ACOK: 3.3V, 24-pin REGN: 6V, 21-pin ILIM: 0.75V, you can see that
there is basically no problem with the chip, and then look at the battery
detection resistor Is it abnormal? After measuring, I found that
everything was normal, but it was a tough nut to crack, and then I turned
directly to the battery interface.
The picture above is the pin
definition diagram at the battery interface. After measurement, the bus read
waveforms of the 3-pin EC_SMB_DA1-1 and 4-pin EC_SMB_CK1-1 are normal, and the
5-pin BATT_TS: 0.2V is abnormal.
This pin is the battery
insertion identification and temperature detection pin directly connected to
the EC to detect whether the battery has been inserted.
Normally, when the battery is plugged in, the 5-pin BATT_TS
detection voltage should be between 1.5V and 2.5V to indicate that the
motherboard has recognized the battery.
However, the actual measurement found that it was only
0.3V. This voltage is pulled up by a 200K pull-up resistor of the external
PR202. After measurement, 200K is normal.
When the detection voltage of pin 5 is below 1.5V, it means that
the EC detects that the battery is overheated. At this time, I directly
suspected that the battery was broken.
I bought a replacement and the fault was still the same. The
maintenance was deadlocked. Then I studied it carefully and found that
there is another signal on pin 6 called BATT_B/I, and then I started to search
for information about what this signal does.
I discovered the mystery. This
signal is equivalent to a protection signal. Now that I know what it is for,
let’s start checking the conditions directly!
In the picture above, we see that BATT_B/I passes through an N-channel
MOSFET and is converted into a BI_S signal to a SW2, a small thing similar to a
switch.
I briefly described the general
meaning in the picture above. Since it is explained that pushing is to turn on,
I directly found SW2 and pushed it.
I found that the charging
current of the battery did change, but the current was very small, only 0.078V.
Then I directly turned it on. I replaced the newly purchased battery and tried
it.
The charging current was around
0.4V and it was normal. Because the bare board was sent without a back cover, I
simply short-circuited pins 1 and 3 of SW2 to simulate this. The back cover has
been closed and the repair is completed.
Repair Result:
Because it is a bare board and
there are no photos of the device turning on, and the external connection
cannot be used, just send a charging waveform!
Happy Repairing !!
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