Lenovo E14 gen. 2, NM-D011, no start

[dhs6512]

Hello, Lenovo Thinkpad E14 Gen.2 Type 20TA, GE4B0/GE5/B0 NM-D011 Rev. 1.0 board. Arrived in the following state: the device is always on and goes in a cycle: the "on" LED lights up, goes out after a few seconds and lights up again, cannot be turned off with the button. Inspection of the board is ok. The charger switches from 5V to 20V. I read that it seems to be a typical problem: the input MOSFETs QB5, QB6 do not open enough and get very hot due to the fact that TPS65994ADYBGR does not supply 28V to the gates. In my case, there were 21.4V on the QB5 gate, 28V on the QB6 gate, but the input MOSFETs do not heat up. The board is leaking, it seems to be approximately in the TPS area. The type-c jack is ok. The TPS strapping is ok. I changed the TPS (took from 2 sources), changed the input MOSFETs, no changes. The voltage of 21.4 V is not constant, but has a sawtooth shape, as if it is trying to reach 28 V and drops to 20 V. Consumption is 4-5 mA. Voltage and resistance on the TPS are ok, there is exchange on CC1 / CC2. I removed the capacitors that could theoretically affect (CB74, 75, 81) and the DB18 diode - no changes. Please tell me what else to look at, what could be leaking, are there really 3 TPS and all of them are defective? Thank you

[mon2]

For each mosfet in the power path, test the resistance with no power to the board.

Measure:

source / drain
drain / gate
gate / drain

Post each measurement. Each should be hundreds of k ohms or higher else the mosfet may be defective. Test QB5 & QB6 for now.

The gate voltage on an N-channel mosfet must be boosted to a higher value than what is being passed between source / drain pins to enable. If you see 28v on QB6, I can only assume that QB5 should be similar unless QB5 is defective.

[dhs6512]

Thank you.
Measured:
QB5
source / drain 1,08kohm
drain / gate 3mohm
gate / drain infinity

QB6
source / drain 1,08kohm
drain / gate 3,1mohm
gate / drain infinity

[mon2]

The source / drain on each is too low. Flux and remove the mosfet(s). Test them again when they are on your workbench. Both may be defective.

[dhs6512]

Thank you, you have right, one of them (was new !!!) was defective, replaced both, now I have 28v at both gates, power consumption 8-12mA

[hamzafox]

The source / drain on each is too low. Flux and remove the mosfet(s). Test them again when they are on your workbench. Both may be defective.

Hello i have same board no power ,Q85 Drain 4,5v source 4,5v
Q86 Drain 4,5 v ssource 0,4 v
I have replaced a new chiip ub7 but to no avail. Please can you help me

[mon2]

,Q85 Drain 4,5v source 4,5v
Q86 Drain 4,5 v ssource 0,4 v

I think you are referencing QB5 & QB6 = AON7466 N-channel mosfets?

Datasheet:

https://www.aosmd.com/sites/default/...ts/AON7466.pdf


Being N-channel, the gate voltage must be higher than the voltage being passed between source / drain pins to enable this solid state switch.

What is the voltage to ground on the GATE pin # 4 of QB5? QB6?

Remove all power. Meter in resistance mode. Measure the resistance to ground of the SOURCE pins (1-2-3) - pick any of these pins. We are testing if there is a shorted part on the main power rail which may be causing this mosfet to remain disabled. Driven by the TBTA_GATE_VSYS signal.

Also, what is the source of UB7? Was it from a donor board or a vendor? Not sure at this time if the chip needs to be pre-flashed to use as this is the PD controller for the logic board so there is a need for firmware. Perhaps the firmware is injected by an outside host on the board or local flash IC or even the main BIOS.

[hamzafox]

I think you are referencing QB5 & QB6 = AON7466 N-channel mosfets?

Datasheet:

https://www.aosmd.com/sites/default/...ts/AON7466.pdf


Being N-channel, the gate voltage must be higher than the voltage being passed between source / drain pins to enable this solid state switch.

What is the voltage to ground on the GATE pin # 4 of QB5? QB6?

Remove all power. Meter in resistance mode. Measure the resistance to ground of the SOURCE pins (1-2-3) - pick any of these pins. We are testing if there is a shorted part on the main power rail which may be causing this mosfet to remain disabled. Driven by the TBTA_GATE_VSYS signal.

Also, what is the source of UB7? Was it from a donor board or a vendor? Not sure at this time if the chip needs to be pre-flashed to use as this is the PD controller for the logic board so there is a need for firmware. Perhaps the firmware is injected by an outside host on the board or local flash IC or even the main BIOS.

Q85 drain 8.80V source 4.95V GATE 4.70V
Q86 drain 8.80V source 0.440V GATE 0.8V
I replaced a new chip UB7 and I don't know if it was programmed before, but I still have the original part.

[mon2]

The drain pin measurements do not make sense. The Vin is ~5v from the USB Type C power adapter so the most you should see is ~5v on the drain pins. Can you confirm the meter you are using is with fresh batteries?



Remove all power. Meter in resistance mode.

Measure the resistance across the mosfet pins:

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Post each measurement. Test both dcin mosfets.

[hamzafox]

The drain pin measurements do not make sense. The Vin is ~5v from the USB Type C power adapter so the most you should see is ~5v on the drain pins. Can you confirm the meter you are using is with fresh batteries?



Remove all power. Meter in resistance mode.

Measure the resistance across the mosfet pins:

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Post each measurement. Test both dcin mosfets.

Q85 source, drane 7,15M OHM
source gate 9,20M OHM
gate drain infinity

Q86 source, drane 7,15M OHM
source gate 9,05M OHM
gate drain infinity

When I connect the MOSFET Q86 to a wire it works but the battery must be connected when I remove the battery the device stops working

[mon2]

The mosfets do not look to be shorted but are not enabled under normal wiring.

When I connect the MOSFET Q86 to a wire it works

?? Provide more details. Which wire? Which pin? Also the mosfets are QB6 - right? Not Q86. Q86 is not showing in my schematic.

Also, with the 'wire connection' - can the power adapter power the logic board or do you still need the battery? The battery cannot power the board unless you connect this bypass wire?

[hamzafox]

The mosfets do not look to be shorted but are not enabled under normal wiring.



?? Provide more details. Which wire? Which pin? Also the mosfets are QB6 - right? Not Q86. Q86 is not showing in my schematic.

Also, with the 'wire connection' - can the power adapter power the logic board or do you still need the battery? The battery cannot power the board unless you connect this bypass wire?

Yes, that's right. I didn't pay attention well. İts QB6

When I remove this mosfet QB6 and connect source with drain with tweezers the device is workink but must battary be connected when i remove the battery the device not working

[mon2]

Measure the voltage again on the drain pins of these mosfets. Red meter probe on drain pin (5-6-7-8); black to ground. This voltage should be the Vin from the USB-C Vbus pin.

[hamzafox]

Measure the voltage again on the drain pins of these mosfets. Red meter probe on drain pin (5-6-7-8); black to ground. This voltage should be the Vin from the USB-C Vbus pin.

QB5 drain 4.66V SOURCE 5V GATE 4.5V
QB6 drain 4.66V SOURCE 0.4V GATE 0.1V