DELL 5520 Laptop That Does Not Turn On

Laptop Model: Dell 5520

Board Number: LA-8412P

Symptom: Laptop does not turn on

　　

Maintenance process:

 First set the adjustable standby 0A

0A is not guaranteed, but it just won't come out in standby mode. I simply disassembled the device and then powered it on. I first tested the isolated rear end and found that the voltage was there.

Continue to test the 3/5V standby power level.

　　Short-circuit the resistor value 3V to ground, find a 3V power stage, except for the ones with resistors, there are only a few left, and finally lock the 1.8VSP power supply. After disconnecting the isolation point, the 3V voltage is not short, and 3/5V is present after powering on.

At first I thought it was a chip problem, but I saw a large capacitor connected to the motherboard.

After removing it and setting the value again, there is no short circuit anymore, the capacitor breaks down, the insulation is connected, and the screen lights up normally.

PS: When the standby circuit of this machine is normal, the ground connection is only a dozen or so. I used an oscilloscope to measure the back end of the inductor. I found that 5V lasted for a while before it dropped, and 3V dropped immediately. It was determined that it was a 3V problem!

 

DELL 14236-1 Laptop Does Not Trigger Repair(Dead)

 DELL 14236-1 Laptop Does Not Trigger Repair(Dead)

Laptop Model: DELL 14236-1

Fault : Notebook Does Not Trigger

Maintenance process: After checking, the common point 13.6V is normal, and the standby 3/5V is normal.

    Refer to the LA-D071P drawing to check the EC. The switch voltage jumps from 2V to 2.8V, and the LID 3.3V is normal. Check the EC to find that the bridge's turn-on signal is 0V, and RSMRST is 0V. There are reports on the forum that flashing the BIOS triggers the problem. The premise is that the BIOS power supply and reading voltage are normal.

　　

And my board is not normal. It is 0.4V for a while and 0.8V for a while. It must be normal in standby. If the BIOS power supply is abnormal and is not short-circuited, it means that the conversion voltage is not coming.

In the picture, the U4101 secondary power supply chip is not installed. A 0 ohm resistor is used to pass it through, and an inductor is found and soldered directly.

You can't tell without careful observation. After installing and testing, the Laptop turned on successfully.

DELL 13269-1 Laptop Does Not Trigger (DEAD CONDITION)

 

Laptop Model: DELL 14-3442

Version number: 13269-1

Fault : The notebook does not trigger and the standby is too high (0.04)

Maintenance process:

 Remove the motherboard and check that there is no burnt appearance or traces of water intrusion. The standby value is 0.04, usually due to short circuit or lack of voltage.

    When plugged in and measured, the common point is 19V, which is normal. The 3V inductor measures 0.59V, and the 5V inductor measures 0V.

Adjust the diode level to 3V5V with no short circuit to ground.

Open the drawing and measure the chip conditions. VREG3 3V is normal and VREG5 5V is normal. EN1 EN2 3.3V is normal, VIN 19V is normal (don't measure VIN just because the linear output is normal, you might be surprised).

Replace the chip directly, plug it in and wait for 0.0093, trigger code running, the connected screen lights up, and the repair is completed.

　　Supplement: Don't worry about the 0.59V on the 3V inductor before repairing it. I have encountered similar problems before and made detours, so I just ignore it this time.

Lenovo IdeaPad 15 2020 Laptop Does Not Trigger (NM-D031)

 

Laptop Model: Lenovo IdeaPad 15S IIL 2020

Motherboard number: NM-D031

Fault: Not Triggered

 

Maintenance process:

 

1. Plug it in, the current is 0.8, the charging is normal, and it does not trigger.

2. Disassemble the machine, unplug the battery, and the bare board power-on standby current is 0.02, sometimes 0.009. Press the switch to trigger normally and start the machine normally. 

The system will automatically power off after about 1 minute and cannot be triggered again. Powering off and on again can trigger booting into the system, and then powering off automatically.

　　3. I thought it was caused by high temperature. Checking the temperature is no problem, the machine is not hot. Temporarily rule out temperature issues first.

        

        4. When the automatic power-off is not triggered, test whether the standby voltage has dropped. After a test, I found that 3V is normal, 3VPG is only 2.9V, and 5V is abnormal, only 2V. Test PU1601, power supply, turn on, linear 5V, all are normal, but the output is 2V. I suspect an IC problem. I don’t have this IC in hand, so I thought of soldering it first. Wind up the gun, solder it once, and test the 5V normal output after it cools down. The system will not lose power when triggered. It's normal even after long-term testing, and it's normal even when it's turned on and off repeatedly. It's considered repaired.

Note: The solder used on this board is low temperature lead. I didn't know at first. It melted within a few seconds after the air gun blew over it.

DELL 5535 Laptop Does Not Trigger When Powered On (LA-9103P)

 

Laptop Model: DELL 5535

Laptop Board Number: LA-9103P

Fault phenomenon: The computer does not trigger when it is powered on.

Maintenance process:

 After receiving a Laptop, it did not trigger when powered on, and the standby test was 3+ 5+, which was normal.

 The switch board button had no voltage, and the resistance value was normal. Which was more than 500. So I found the drawing LA-9103P and measured it according to the maintenance ideas. , the standby conditions are all normal, the problem is that ON/OFF is not raised, because the designer is too labor-intensive, the motherboard components are not fully marked, RE49 cannot be found, but the +3VLP measured is normal output, through the PU200 chip, As shown in the picture .

I'm a little bold, and imagine changing the circuit, using enameled wire to connect the 100M resistor directly to the third pin of the switch JPWR, as shown in the picture

So I found a 100M resistor from the scrap board, directly connected the 3rd pin of the PU200 to the first pin of the 100M resistor, and connected the 2nd pin of the 100M to the 3rd pin of the JPWR. Press the on/off button to trigger the connection and the screen will turn on Laptop.

Lenovo E14 & E15 Are Not Charging Problem

 

Laptop Model: Lenovo E14, E15

Laptop Board Number: NM-D011

Fault: Not charging

　　

 

Maintenance process:

    After disassembling the Laptop and unplugging the battery, the voltage at the common point of the single-plug power supply was 3.0 volts, and it kept jumping.

　　Looking forward, VINT20_IN also has no voltage, and continuing forward, this voltage is generated through the conversion of QB5 and QB6.

The front and rear voltages of QB5 are normal. The Gate of QB6 is normal, the Drain level is normal, the Source has no voltage, and the Mosfet has not broken down. I want to try another one first. When the air gun blew, the Mosfet flew away. I looked at the soldering pad and MOSFET and found that they were completely desoldered.

Decisively, the pads and Mosfet were plated with solder, the tubes were welded on, the plug-in current brushed up, and the power was turned on for a test. The charging sign came out, and the repair was completed.

 

Lenovo G400S LA-9910P Shuts Down In About 30 Seconds

 

Laptop Model: Lenovo G400S

Motherboard ID: LA-9910P

Problem : Shuts Down In About 30 Seconds

 

　　Fault phenomenon: The phone can be turned on normally when triggered. During the process of entering the system, it loses power and shuts down. After power failure and shutdown, it can be triggered to turn on again, and it will automatically shut down again when it is about to enter the system.

 

　　Maintenance process: At first I thought it was caused by high temperature, but I didn't feel overheating when I touched the copper pipe. So, I took out the motherboard and tested it with the bare board, and it was the same. I counted silently in my mind before shutting down the phone in about 33 or 34 seconds. 

 

I checked the PROCHOT# and THERMTRIP# signals of the CPU over-temperature module and found nothing abnormal. So searched for the CPU temperature module (THERMAL) in the drawing, it found that there were two signals CATERR# and PECI.

H-CATERR# is only connected to one test point externally and not to other places. The PECI signal is connected to EC pin 118 through a 43 ohm resistor. I used a magnifying glass to observe pin 118 of the EC.

There seemed to be a black spot on this pin. I poked it with a test pen and found the fault point. It was the disconnection of the PECI signal that caused poor communication between the CPU and EC, so I repaired the fault by patching the line.

Happy Repairing !

Lenovo ideapad 320s-15ISK CIUYA/YB/SA/SB/SD LA-E541P NOT CHARGING

 

Laptop Model: Lenovo Ideapad 320S-15ISK CIUYA/YB/SA/SB/SD LA-E541P

Fault : Not charging

Repair Process:

I took the machine and tested it and found that it could be turned on. However, when I entered the system, I found that only the battery was usable and the power symbol was not displayed when the power was plugged in.

 

After shutting down and disassembling the machine, I found that the charging chip had been replaced. The battery chip is: 88739A. There are also obvious traces on the isolation Mosfet at the power connector. When the battery is unplugged and the power supply is turned on, the computer can be turned on and used normally.

 

If the battery is turned on , the computer can be turned on normally. However, the battery and the power supply are connected at the same time, and the current jumps and causes a short circuit.

 

 

The main board was removed. Board number: LA-E451P. Independent machine. Use a Multimeter to measure the voltage and plug it into the battery. Then plug it in and find that the isolation directly becomes 1V. 

The upper and lower Mosfets  of the battery management chip circuit PQ706 PQ305 have 11V on one side and 11V on the other side.

I also measured the 1.5V of pin 11 of the 88739 chip and felt something was wrong, so I replaced the voltage dividing resistor with 200K and 154K. I didn't have 154K, so I found a 150K instead, and the result was still the same.

 It seems that the only option is to try to replace PQ706 and PQ305. Unexpectedly, the power-on test with normal results started to fail again within 5 minutes. Is the pipe wrong? After disassembling it again for testing, the final result revealed that it was caused by leakage of the 19V Mosfet on the standby chip. Replacement solved the problem.

Repair Process completed.