Lenovo 100-15idb NM-A681 no turning on

[mon2]

Re: Lenovo 100-15idb NM-A681 no turning on

Yes. Agree that this component is likely defective.

You can check the same resistance values on the component while it is on your work table.

Check the resistance between:

source & drain
source & gate
gate & drain

There are 2 such mosfets inside this single package so check both.

A low resistance on any of the above checks means the mosfet is defective.

With the logic '1' = ~3v on the gate on a 2N7002, the mosfet should be ON.

When the mosfet is ON, the lower resistor on the above portion of the schematic will build a voltage divider to lower the Vin voltage. When the gate voltage is at a lower potential, the P-channel mosfets (DCin) will enable and then pass the voltage onto the main logic board.

As a quick test, now that this dual mosfet is removed, ground the gate pin of the DCin mosfets. This will force the DCin mosfets to enable.

[xRaPiDxX]

Re: Lenovo 100-15idb NM-A681 no turning on

Thanks for help, I replaced PQ307. Now laptop turns on but with no display, cpu is cold.
I measured coils:
PL9: 1.6985V
PL701: 1.0474V
PL304: 5.078V
PL303: 3,371V
PL501: 1,3557V
Bios chip Has 3,370V.
Power supply consumes 0.098a when turns on.
If I shutdown through button it consumes 0.011a.
I programmed bios and changed ram nothing changed.

[mon2]

Re: Lenovo 100-15idb NM-A681 no turning on

Power supply consumes 0.098a

That is 98 mA and is a very low current for a laptop.

Check the voltage to ground on each power rail / coil. Someone is off.

Confirm the main power rail voltage to ground after the DCin mosfets.

[xRaPiDxX]

Re: Lenovo 100-15idb NM-A681 no turning on

I measured coils, measurments in attachments and checked pq40 and pq39. Should I replace them because of low resistance?

PQ40
S:4,45 voltage to ground
G:16,148 voltage to ground
D:20,10 voltage to ground
diode test: 0,53V
Source - drain: 2mohm and goes down (no power)
Source - Gate: 1ohm (no power)
Gate - drain: 13mohm and goes down (no power)


PQ39
S:0 voltage to ground
G:4,4528 voltage to ground
D:4,32 voltage to ground
diode test: 0,0767V
Source - drain: 37,48ohm (no power)
Source - Gate: 10mohm and goes down (no power)
Gate - drain: 11mohm and goes down (no power)

[mon2]

Re: Lenovo 100-15idb NM-A681 no turning on

Yes, they both look bad but remove each and check their resistance again when they are off the logic board and on your work table.

If the resistance remains to be low, replace the mosfet.

Post the measurements. On a good mosfet, the resistance should be high.

Start with removing one mosfet to check if it impacts the resistance of the other.

[xRaPiDxX]

Re: Lenovo 100-15idb NM-A681 no turning on

PQ40 without PQ40:
Source - drain: 1.8mohm and goes down (no power)
Source - Gate: 2.3kohm and goes up (no power)
Gate - drain: 0.75mohm and goes down (no power)


PQ39(soldered) without PQ40:
Source - drain: 36,47ohm (no power)
Source - Gate: 10mohm and goes down (no power)
Gate - drain: 6.4mohm and goes down (no power)


PQ39 without PQ 39:
Source - drain: 32,87ohm (no power)
Source - Gate: 10mohm and goes down (no power)
Gate - drain: 5.5mohm and goes down (no power

PQ40(soldered) without PQ39:
Source - drain: 0.63mohm and goes up (no power)
Source - Gate: 0.2833mohm (no power)
Gate - drain: 0.79mohm and goes down (no power)

So source - drain on PQ39 is still low. Should I first try to replace both mosfets?

[mon2]

Re: Lenovo 100-15idb NM-A681 no turning on

Appears that PQ39 is the defective one so yes, replace it.

[xRaPiDxX]

Re: Lenovo 100-15idb NM-A681 no turning on

Okay so I replaced PQ39 still no display, CPU cold.

NOW:
PQ39
S:0 voltage to ground
G:4,4519 voltage to ground
D: ~8,50 voltage to ground

Source - drain: 35,46 ohm (no power)
Source - Gate: 9,812 mohm (no power)
Gate - drain: 6,382 mohm (no power)

Power consumption is the same.

[Stevedb]

Re: Lenovo 100-15idb NM-A681 no turning on

If you got the same reading without mosfet on pq39.
Then there is something else what partial shorted is .you mus find first what that is before you continue. Is there shematic available?

[xRaPiDxX]

Re: Lenovo 100-15idb NM-A681 no turning on

Yes schematic and boardview are available. I use them from this post: https://www.badcaps.net/forum/showth...37#post1044937
Yes, but I do not know where to start measuring now.

[xRaPiDxX]

Re: Lenovo 100-15idb NM-A681 no turning on

I have 32ohm on the second pin of PC97. Should I remove PU908 to check if resistance increase or is 32 ohm good for this line?

[Stevedb]

Re: Lenovo 100-15idb NM-A681 no turning on

When one off the buck converter is defect you need to Replace the low side , high side and driver ic together. I will remove pq38 , pq39 and pu908 and see if you have still the low reading on D-S on pq39 .

[xRaPiDxX]

Re: Lenovo 100-15idb NM-A681 no turning on

I removed PQ39, PQ40 and PU908.
S-D on PQ39 now: 36,18ohm

[Stevedb]

Re: Lenovo 100-15idb NM-A681 no turning on

You need to remove the partial short. How much resistance you have to ground there S -Ground.

[xRaPiDxX]

Re: Lenovo 100-15idb NM-A681 no turning on

PQ39 (no soldered) resistance to ground
S: GND
G: out of range
D: 37,68ohm

PQ40 (no soldered) resistance to ground:
S: 37,98 ohm
G: out of range
D: 0,36 mohm and increase

[Stevedb]

Re: Lenovo 100-15idb NM-A681 no turning on

Do you have power supply inject 0.9v 1A and increase amps if needed but not the voltage and see what is getting hot.

[xRaPiDxX]

Re: Lenovo 100-15idb NM-A681 no turning on

With 0.9V it consumes only 0.030A. I can not feel any heat using my hands. I do not have thermal camera. Can I increase voltage?

[mon2]

Re: Lenovo 100-15idb NM-A681 no turning on

See attached. Can you confirm that the measurements are from the correct mosfets?

It is important to confirm as the ~37 ohms to ground may very well be the CPU rail resistance.

Take the resistance to ground @ PL9 inductor - remove all power.

What is the resistance @ PL9 ?

[xRaPiDxX]

Re: Lenovo 100-15idb NM-A681 no turning on

PL9 resistance to ground (NO PQ39, PQ40, PU908 soldered)
PIN 1 - 35,86 ohm
PIN 2 - 36,32 ohm
so is this line correct?

[mon2]

Re: Lenovo 100-15idb NM-A681 no turning on

This is the CPU vcore rail and by design, it will be a low voltage and respectively is a low resistance to ground rail.

Unless this rail is extremely low in resistance, this resistance reading looks ok to me. If the CPU was shorted, then you may see extremely low resistance readings like 1 ohm or less.

You can measure the resistance of the removed mosfets while they are off the logic board. If the mosfet readings are high then place them back.

Each, the high side and the low side work together to lower the very high voltage used by the logic board to a safe value for the CPU core.

After the above, confirm if the switching regulator for this rail is being enabled or not. This is pin # 1 of PU908.

In either case, do not power up till both mosfets are onboard and confirmed to be soldered ok. Otherwise, if for example ONLY the high side mosfet is soldered but the low side is removed, then the regulator @ PU908 will assume both onboard and the CPU will be killed since there is no mosfet to lower the high voltage. Both mosfets must work together to lower the voltage to a safe value.