Lenovo IdeaPad S340-15IWL charging not working

[radoslav baca]

Hello everyone,

Description : Lenovo
Model : 81N8
Serial Number :MP1LFDME
Product Number : PRC4
CN :
MFD: 19/05/30
MTM : 81N800BGCK
Hard disk : NVMe 256GB P/N SSS0R27339
CPU: Intel Core i3 8th generation
RAM : DDR4 K4A8G16 4 x chip

MB : EL5C3/EL531/EL431 LA-H101P Rev 1.0 2018/12/12

Hello everyone,

I have a problem with my laptop. When I measure the connector where the adapter is connected between + and - it shows almost 0V. If I disconnect the connector from the motherboard, I measure between + and - 20 V. Can you advise me what the error is or what needs to be measured? I had the battery disconnected from the motherboard during the measurement.

[mon2]

Attached.

Remove all power. Meter in resistance mode. Measure the resistance to ground on the main power rail (PL1 is ok; either side) that mates with the DCin power connector. Checking if the main power rail is shorted. What is the resistance in ohms?

One meter lead to ground; other meter lead on PL1. Either meter lead color is ok.

[radoslav baca]

Attached.

Remove all power. Meter in resistance mode. Measure the resistance to ground on the main power rail (PL1 is ok; either side) that mates with the DCin power connector. Checking if the main power rail is shorted. What is the resistance in ohms?

One meter lead to ground; other meter lead on PL1. Either meter lead color is ok.

I measured PL1 and PF1 on both and it showed 305K ohms to ground.

[mon2]

Review PQ311 and PQ312. No power to the board. Meter in resistance mode.

Measure the resistance across these mosfets:

source / drain
source / gate
gate / drain

Post each measurement. Each measurement should be hundreds of k ohms or higher. Otherwise the mosfet may be defective.

[radoslav baca]

Review PQ311 and PQ312. No power to the board. Meter in resistance mode.

Measure the resistance across these mosfets:

source / drain
source / gate
gate / drain

Post each measurement. Each measurement should be hundreds of k ohms or higher. Otherwise the mosfet may be defective.

PQ311
S - D - 0,7 ohm
S - G - 1ohm
G - D - 1,3 ohm

PQ312
S - D - 294K ohm
S - G - 1 ohm
G - D - 304K ohm

I found a datasheet for the PQ311 showing how the pins are arranged, but not for the PQ312, but I went according to what was shown on the pq311, that 4 pins are Drain, 3 pins are Source and 1 pin is Gate.

[mon2]

Both look nasty and shorted but start with fluxing and removing PQ311 off the board. Then (without power), measure the resistance again on PQ312. Need to confirm if the resistance values improve or not - especially the S/G @ 1 ohms.

[radoslav baca]

Both look nasty and shorted but start with fluxing and removing PQ311 off the board. Then (without power), measure the resistance again on PQ312. Need to confirm if the resistance values improve or not - especially the S/G @ 1 ohms.

I removed PQ311 from the motherboard and measured PQ312. G - S 1 ohm S - D 570K ohm and G - D - 575 K ohm

[mon2]

G-S is still low. Flux and remove this 2nd dcin mosfet. Also test the removed mosfet while it is on your workbench. Then measure the pcb pads in the same way. Still have a short? Also interested in the resistance to ground of each pin to confirm there is no other fault.

[radoslav baca]

G-S is still low. Flux and remove this 2nd dcin mosfet. Also test the removed mosfet while it is on your workbench. Then measure the pcb pads in the same way. Still have a short? Also interested in the resistance to ground of each pin to confirm there is no other fault.

I also disconnected the second mosfet. When it was warm, it showed some values, but terribly high, over 700 K ohms. When it cooled down, I didn't measure anything anymore and the meter showed 0L between D-S and D-G. I also attach a photo when I measured the pins on the board. I measured the plus and minus from the other side of the connector to the other side of the board on the pin to see if there was a short circuit and everything beeped. Then I measured the internal pins and according to the picture you can see how they worked with each other.

[mon2]

Ok back from mind numbing grocery shopping. Each of the removed mosfets is with a high resistance for the above method of testing?

Test the PCB pads on the logic board. If the logic board is now with high resistance when testing only the PCB pads, then the mosfets are to blame. Clarify the details. Also interested in the resistance to ground of each pin on the PCB pads where these mosfets were soldered.

Need to be sure that the main power rail is not shorted.

[radoslav baca]

Ok back from mind numbing grocery shopping. Each of the removed mosfets is with a high resistance for the above method of testing?

Test the PCB pads on the logic board. If the logic board is now with high resistance when testing only the PCB pads, then the mosfets are to blame. Clarify the details. Also interested in the resistance to ground of each pin on the PCB pads where these mosfets were soldered.

Need to be sure that the main power rail is not shorted.

I measured through the resistor and the picture shows the result. Where I measured 365K ohm is the plus pole. I also measured the disconnected mosfet PQ311 and between all legs I measured 1 ohm, so this mosfet will be good. Mosfet PQ312 shows me infinity 0L.

[mon2]

See attached. Is this area shorted?

Test the removed mosfets. At least must be shorted to cause the readings reported earlier.