Lenovo G50-30 Completely dead, no lights at all.

[Andreasbest]

Hello.
I received today a laptop for repair that had probably a short circuit in DC jack.
Has no response at all, neither battery charging, neither on pressing power on.
The picture is from the "modification" the customer made and lead me to thought of short circuit i told you before.
Schematics of M/B uploaded.
Thanks in advance!!!

[BlueMidnight]

Re: Lenovo G50-30 Completely dead, no lights at all.

Hello again.

Alright, so the first thing we need to know is if the AC adapter works. It's possible it could have shorted at the spot in your picture. That may not damage the adapter though. They are usually pretty smart about shutting down when shorted. Well.. good ones are anyway.

Test the voltage. It should have 20V between positive and ground. There is also an ID pin in the center. There is a resistor inside it that connects that pin to ground. The value of the resistor will tell the notebook the wattage of the AC adapter. The notebook won't run/charge if it thinks the AC adapter isn't powerful enough.

Common values of the resistor:
45W = 120 ohms
65W = 280 ohms
90W = 550 ohms

Even if the AC adapter measures okay with a multimeter, it still might not work properly under load. It's always useful to have another adapter to try. A universal adapter with many different tips is a good investment.

If the AC adapter is working, then the next thing to do is follow the power on the motherboard itself.

Check that you get 20V on JDCIN1 pins 1-2 (page 51). If it is there, then follow it through the fuse PF101.

Next, make sure you can read 20V on both sides of PQ301 and PQ302 (page 53). If so, check the 3V and 5V regulators PU401 and PU402 (page 54). Check the LDO and the main output on both. If they aren't working, check for shorts.

It's also a good idea to test the "ADAPTER_ID" pin (pin 3 of JDCIN1) to make sure it does not have a short to ground (with the AC adapter unplugged).

[Andreasbest]

Re: Lenovo G50-30 Completely dead, no lights at all.

Thank you very much for the help
Ok hold on, if this adapter has 3 pins it means it should got 3 wires too, correct?
Because as i see the customer has "connected" only 2 wires in charger damaged cable, so we miss one?

[BlueMidnight]

Re: Lenovo G50-30 Completely dead, no lights at all.

You're welcome.

The resistor is actually in the connector part of it. So they didn't need to add a 3rd wire in the cable.

Some AC adapters, like for Dell notebooks, do have an extra wire because the center pin is a serial data communications pin. But the Lenovo ones keep it really simple. No communication. Just a little resistor.

[Andreasbest]

Re: Lenovo G50-30 Completely dead, no lights at all.

Charger gave me 119Ω so i think it's ok (45w)
I get 20v on pin 1 and pin 2.
I also get 20v on both sides of PQ301 but on the PQ302 i get them only to the one side (the side that "looks" to PQ301) the other side gives readings of only 0,9v on all pins.

[BlueMidnight]

Re: Lenovo G50-30 Completely dead, no lights at all.

Okay good, now we know where the 20V stops.

Next, measure voltage on PQ302 pin 4. If it's 0V then PQ302 is probably bad. If pin 4 is around 20V, then unplug the power and check for a short between PQ302 pins 5-8 (they're all connected) and ground.

If there is a short, then it will be time for a fun short-finding expedition.

If there is no short, then measure all pins on PU301 (20 pins total). Also measure all pins on PQ306, PQ308, PQ309, and PQ310 (they each have 6 pins).

Waiting for messages back and forth is the longest part. Better to do as much measuring as possible.

I'm off to bed. Be back later.

[Andreasbest]

Re: Lenovo G50-30 Completely dead, no lights at all.

PQ302 has 20v in pin 4 so i proceed with PU301
1 0.9v
2 0.9v
3 0
4 0.7v
5 0
6 2.6v
7 0
8 0
9 0
10 0
11 0.6v
12 1.3v
13 1.3v
14 0
15 0
16 6v
17 6v
18 1.2v
19 1.2v
20 20v
also PQ306
P1 0
P2 3.3
P3 0
P4 0
P5 3.3
P6 0
and PQ308
P1 0
P2 0
P3 0
P4 0
P5 0
P6 20
and PQ309
P1 0
P2 0
P3 3.3
P4 0
P5 0
P6 3.3
PQ310 is not soldered on board at all, just the marking.
Sleep well and we'll talk later

[BlueMidnight]

Re: Lenovo G50-30 Completely dead, no lights at all.

PC307 is probably bad/shorted.

Everything you measured tells me you are supposed to be getting 5V on pin 4 of PQ302 right now. But you are not. So the 20V must be shorted through either PC307 or PQ304. But a bad capacitor is more likely.

Measure the resistance across PC307. It is probably at/near 0 ohms. If so, remove it and test it out of circuit to make sure it's still 0 ohms.

Also, test the pads to make sure the short is gone with the capacitor removed. If so, then you've found your problem.

The component is an 0402 sized 0.1uF 25V ceramic capacitor.

[BlueMidnight]

Re: Lenovo G50-30 Completely dead, no lights at all.

I forgot to mention the next step.

If PC307 is good, check PQ304 pin 2 when powered. If it's 20V then PQ305 is good. Otherwise PQ305 is bad.

If PQ305 is good, then remove and test PQ301 and PQ304.

PQ301 is a MOSFET and you know how to test that. Except the on and off states are reversed since it's a P-Channel.

PQ304 will measure like it is 2 diodes connected together at pin 2. Black on 2, red on 1 or 3 = 0.5V. Swap leads and it's open circuit.

[Andreasbest]

Re: Lenovo G50-30 Completely dead, no lights at all.

I tested PC307 on circuit measures 180Ω ,when i removed it i got 10MΩ and was increasing for as long i was taking measure 11MΩ,12ΜΩ,13ΜΩ and so on.
PQ304 has 20v an all three pins, PQ305 has 20v only on pin 1,PQ301 has 20v on all pins.
I removed PQ304 from circuit and gives no measures at all, with black on pin 2 and red on 1-3 and the opposite with multimeter in diode mode.
Just to make sure, PQ304 pin 2 is the one that is directly connected with the pin 1 of PQ305, correct?
Also in Ω mode the PQ304 shows various resistance on all pin combinations, i think the pin 1 should not give any resistance at all.
Now i'm confused though, how is it possible the PQ304 to be faulty but the same time to have output 20V to PQ305 that hasn't output at all?!

[BlueMidnight]

Re: Lenovo G50-30 Completely dead, no lights at all.

It sounds like PQ305 is good.

Yes, PQ304 pin 2 is connected to PQ305 pin 1. The 20V on pin 2 gets there through the biasing resistors that are built into that transistor. You can see them drawn on the schematic. The blue circle is indicating that everything inside the circle is inside that one component.

PQ304 is a PNP transistor and should never have 0 ohms between any 2 pins. I suspect you are reading nothing in diode mode due to the biasing resistors and the low power used by the multimeter. That's okay for now. We are looking for a shorted component and it seems PQ304 isn't it.

PR303 and PR308 form a resistor divider with 20V on one side and 0V on the other. That should give about 5V in the middle. And a voltage that low will turn on PQ301 and PQ302. But it doesn't have 5V. It has 20V. And 20V turns them off. So, there must be a low-resistance path around/through PR303. The only thing that is designed to do that is PQ304, but PQ304 is supposedly off (It should only turn on if PQ305 turns on and pulls PQ304 pin 2 down to 0V). Therefore, there must be a short circuit through something (i.e. a bad component).

I'm attaching a picture that shows the voltages you have measured and the corresponding state of all the transistors. I find it very useful to write voltages on the schematic like this. The orange arrows show the only possible paths for the 20V to get where it is now.

There are no other options except for things like physical shorts between traces on the board. The following are the only components that could be bad:

You tested these...
PC307
PQ304

You didn't mention removing and testing these yet...
PQ301
PQ302
PR303

I listed only the most likely causes before, but remove and test every single one of those if you have to.

[BlueMidnight]

Re: Lenovo G50-30 Completely dead, no lights at all.

Forgot to add PR308 to the list also.

[Andreasbest]

Re: Lenovo G50-30 Completely dead, no lights at all.

Hello again.
Back from vacation and back on repairs.
When you say the ON and OFF states are reversed you mean
1) Red on Drain, Black on Gate (No connection. This also turns the MOSFET ON)
2) Red on Drain, Black on Source (No connection)
3) Swap the probe positions. Red on Source, Black on Drain (One diode drop, approximately 0.5V)

4) Red on Gate, Black on Drain (No connection. This also turns the MOSFET OFF)
5) Red on Source, Black on Drain (Less than 0.2V)
6) Swap the probe positions. Red on Drain, Black on Source (Less than 0.2V)

7) Repeat steps 1-3 to make sure MOSFET turns off again successfully
Did i understand correctly?

[BlueMidnight]

Re: Lenovo G50-30 Completely dead, no lights at all.

Yes, for a P-Channel MOSFET, black on the gate will turn it ON and red on the gate will turn it OFF. The body diode faces the opposite way also. So, STEP 2 would read as 0.5V and STEP 3 would read as no connection.

I also want to clarify that when I mentioned PR308, I meant PR308 going open circuit will cause the same symptom as any of the others I listed going short circuit. And it looks like it has nothing else in parallel, so you should be able to measure its resistance without removing it.

[Andreasbest]

Re: Lenovo G50-30 Completely dead, no lights at all.

Here are the measurements from PQ301 and proceeding to PQ302 and PR303
1) Red on Drain, Black on Gate 0,21
2) Red on Drain, Black on Source 0,030
3) Swap the probe positions. Red on Source, Black on Drain 0,030

4) Red on Gate, Black on Drain 0,21
5) Red on Source, Black on Drain 0,030
6) Swap the probe positions. Red on Drain, Black on Source 0,029
Also please point me the PR308 on the picture as i cannot found it.

[BlueMidnight]

Re: Lenovo G50-30 Completely dead, no lights at all.

Looks like you found the problem. PQ301 is shorted. There should never ever be continuity between the gate of a MOSFET and either the source or drain. Also, it obviously does not turn on/off properly.

I can't see the traces well enough in the picture to find PR308, but it is connected to pin 3 of PQ306 and I do see that. So it might be one of those resistors next to it, or it might be on the other side of the board.

There is a chance multiple components are bad, but usually it's just one. You might not have to find PR308. There's no harm in just replacing PQ301 and checking if the board works.

[Andreasbest]

Re: Lenovo G50-30 Completely dead, no lights at all.

Is there a chance to took measurments the wrong way? Perhaps should i start measuring with another order or from different pins or while it's ON or OFF etc?

[BlueMidnight]

Re: Lenovo G50-30 Completely dead, no lights at all.

The order is fine. Order doesn't matter in this case though. Under no circumstances should the gate ever be electrically connected to the other pins of a MOSFET.

[Andreasbest]

Re: Lenovo G50-30 Completely dead, no lights at all.

Ok fixed it.
I just don't understand why we had 20v to output but was still faulty! It should be dead, isn't?

[BlueMidnight]

Re: Lenovo G50-30 Completely dead, no lights at all.

Normally, 20V goes through PQ301 because of the body diode (even if it's turned off). Then the resistors PR303 and PR308 (a resistor divider) cause the voltage at the gates of PQ301/PQ302 to be 5V. That turns them both on.

MOSFETs usually fail shorted (unless they have just blown/burned up). In this case, PQ301 was shorted to the gate. And because the gate of PQ301 is connected directly to the gate of PQ302, PQ302 always had 20V on its gate too. So it was forever being told to stay turned off.

If the board needs to turn off PQ301/PQ302 for some reason, it will turn on PQ304 to bypass PR303 and send 20V to both gates. The shorted MOSFET was doing the same thing, except permanently.