ACLU2 (G50-70) Motherboard Not Powering On

[orestes_]

Hello,

As the tittle suggests, the laptop does not want to power on. It is completely dead (no LEDs or the CPU/GPU fan spinning).

Motherboard does received power, connector and the connector cable do work.

I can hear a clicking sound coming from the motherboard every ~1.5s, I assume there is a open circuit somewhere that is causing all this trouble. I cannot pinpoint the location of the fault by ear, it sounds the same no matter where I place my ear.

Nothing is hot or even warm to the touch. Super I/O chip does not appear to be damaged, so one or more conditions do not allow the unit to power on?

Can you please advise what to check, very detailed because of my limited experience?

Thanks.

[mon2]

Re: ACLU2 (G50-70) Motherboard Not Powering On

hi.

1) start with posting some clear pics of the logic board and show where the DC adapter enters the board.

2) are you using the original DC adapter for this laptop ? What is the voltage that enters this logic board ?

3) you should note some mosfets mating to the DC power connector. The mosfets are like solid state relays to turn on / off the power rail for the logic board. Quite often, these mosfets get damaged and produce the observed condition.

4) For each mosfet - post the full markings on the topside of the device. This will help to locate the datasheets for further trouble shooting.

Asus schematics are quite rare and so far unable to locate one for this logic board.

Do you have a multimeter ?

[orestes_]

Re: ACLU2 (G50-70) Motherboard Not Powering On

hi.

1) start with posting some clear pics of the logic board and show where the DC adapter enters the board.

2) are you using the original DC adapter for this laptop ? What is the voltage that enters this logic board ?

3) you should note some mosfets mating to the DC power connector. The mosfets are like solid state relays to turn on / off the power rail for the logic board. Quite often, these mosfets get damaged and produce the observed condition.

4) For each mosfet - post the full markings on the topside of the device. This will help to locate the datasheets for further trouble shooting.

Asus schematics are quite rare and so far unable to locate one for this logic board.

Do you have a multimeter ?

I think you misunderstood, this is in fact a Lenovo laptop. It is the G50-70 with a 4th gen i3 and an basic AMD discrete GPU. The ACLU2 is, I think, the codename for this motherboard. There is also a thread on this forum, I think there are all the schematics needed there:

https://www.badcaps.net/forum/showthread.php?t=72373

1. pic attached

2. 20V in, as the adapter states on the sticker. it is the original Lenovo one.

3/4. there are 2 mosfets near the DC in on the mainboard, 4488A and 4407A.

I do have a multimeter and I know how to solder but unfortunately I do not have a hot air station .

thanks. 👍

[mon2]

Re: ACLU2 (G50-70) Motherboard Not Powering On

See attached.

Meter in DC voltage mode (any setting with 20V or higher is ok).

1) check the voltage reading with the adapter plugged in on both sides of the surface mount fuse (it is the white component).

Red meter lead on the one pad & black meter lead on any ground on the logic board (can be metal shield).

2) If you do see the adapter voltage on BOTH sides of the fuse, continue to check the mosfets as per attached diagram.

3) the white DOT on the part = pin # 1. See my Picasso drawing that shows how the pin order is for each mosfet.

Check and post the voltages on each requested pin.

Note that the pins are shorted together (on purpose) as per the schematic so you only need to check the voltage on any of these pins.

In these tests, you are checking if the first in-line fuse is blown or not.

Then you are checking to see if the first 2 mosfets are working properly or not.

PS: For now, you do not need the hot air station. These mosfets, if they need to be replaced are SOIC 8 style. Using some sharp diagonal shears / cutters, you can remove them off the board and apply a fresh one. We are not there yet so for now, ignore.

[orestes_]

Re: ACLU2 (G50-70) Motherboard Not Powering On

See attached.

Meter in DC voltage mode (any setting with 20V or higher is ok).

1) check the voltage reading with the adapter plugged in on both sides of the surface mount fuse (it is the white component).

Red meter lead on the one pad & black meter lead on any ground on the logic board (can be metal shield).

2) If you do see the adapter voltage on BOTH sides of the fuse, continue to check the mosfets as per attached diagram.

3) the white DOT on the part = pin # 1. See my Picasso drawing that shows how the pin order is for each mosfet.

Check and post the voltages on each requested pin.

Note that the pins are shorted together (on purpose) as per the schematic so you only need to check the voltage on any of these pins.

In these tests, you are checking if the first in-line fuse is blown or not.

Then you are checking to see if the first 2 mosfets are working properly or not.

PS: For now, you do not need the hot air station. These mosfets, if they need to be replaced are SOIC 8 style. Using some sharp diagonal shears / cutters, you can remove them off the board and apply a fresh one. We are not there yet so for now, ignore.

Thank you for the detailed instructions, here you go:

Fuse is OK (20V in and 20V out).

With reference to Gnd:

Mosfet #1 (4488A):

Pin 1: 19.91 V
Pin 2: 19.91 V
Pin 3: 19.91 V
Pin 4: 19.91 V

Pin 5: 0V
Pin 6: 0V
Pin 7: 0V
Pin 8: 0V

Mosfet #2 (4407A)

Pin 1: 19.91 V
Pin 2: 19.91 V
Pin 3: 19.91 V
Pin 4: 19.91 V

Pin 5: 20.44V
Pin 6: 20.44V
Pin 7: 20.44V
Pin 8: 20.44V

[mon2]

Re: ACLU2 (G50-70) Motherboard Not Powering On

Ok.

1) PQ301 = mosfet p/n AO4407AL

2) PQ302 = mosfet p/n Si4483ADY (last digit is a '3') - from the posted values, this 2nd mosfet in the design is not turning on since DRAIN pins are @ 0V.

PQ302 is a P-channel mosfet (see attached) - specifically P-Channel Enhancement Type MOSFET (the broken dash lines inside the circle denote enhanced type).

http://www.learningaboutelectronics....hannel-MOSFETs

To turn PQ302 ON, the gate has to be lower than the voltage value on the SOURCE. The present reading is that the GATE (pin # 4) matches the input voltage of about 19V.

To turn ON this mosfet, PACIN or BATT_OUT has to be a positive value such as +3v to turn on the local mosfets (2N7002) which will then apply a GROUND to the mating resistors.

Once the local mosfets are ON, a resistor voltage divider is created which will then divide the +19V down to a lower value which will then turn on the PQ302 mosfet through the lower gate value.

That is, when 2N7002 @ PQ307B is ON, then PR303 & PR307 form a resistor based voltage divider with +19V as the high side voltage. Together these resistors will offer a lower voltage @ GATE of PQ302.

If the 2N7002 is OFF (default) then only PR303 is active and it will pull the GATE to be @ +19V which means that PQ302 will remain OFF.

For these other 2N7002 mosfets to work, the 'always-on' rails must be working.

See and check the attached. Post their values.

[orestes_]

Re: ACLU2 (G50-70) Motherboard Not Powering On

Ok.

1) PQ301 = mosfet p/n AO4407AL

2) PQ302 = mosfet p/n Si4483ADY (last digit is a '3') - from the posted values, this 2nd mosfet in the design is not turning on since DRAIN pins are @ 0V.

PQ302 is a P-channel mosfet (see attached) - specifically P-Channel Enhancement Type MOSFET (the broken dash lines inside the circle denote enhanced type).

http://www.learningaboutelectronics....hannel-MOSFETs

To turn PQ302 ON, the gate has to be lower than the voltage value on the SOURCE. The present reading is that the GATE (pin # 4) matches the input voltage of about 19V.

To turn ON this mosfet, PACIN or BATT_OUT has to be a positive value such as +3v to turn on the local mosfets (2N7002) which will then apply a GROUND to the mating resistors.

Once the local mosfets are ON, a resistor voltage divider is created which will then divide the +19V down to a lower value which will then turn on the PQ302 mosfet through the lower gate value.

That is, when 2N7002 @ PQ307B is ON, then PR303 & PR307 form a resistor based voltage divider with +19V as the high side voltage. Together these resistors will offer a lower voltage @ GATE of PQ302.

If the 2N7002 is OFF (default) then only PR303 is active and it will pull the GATE to be @ +19V which means that PQ302 will remain OFF.

For these other 2N7002 mosfets to work, the 'always-on' rails must be working.

See and check the attached. Post their values.

Took me a while to find them 😅.

You can see in the pictures the said area of the PCB and how I probed them.

It reads 0V on both of them.

[mon2]

Re: ACLU2 (G50-70) Motherboard Not Powering On

I think the measurements were not taken properly for the black (ground) lead.

Please see attached and repost after checking again.

[orestes_]

Re: ACLU2 (G50-70) Motherboard Not Powering On

I think the measurements were not taken properly for the black (ground) lead.

Please see attached and repost after checking again.

indeed, I am stupid.

however, there is no voltage present on both of them even when with reference to ground.

[mon2]

Re: ACLU2 (G50-70) Motherboard Not Powering On

hi.

1) see attached. check and post the voltages at '1' and then for '2' on PU904.

Meter in DC mode (20v or higher is ok).

Red meter at the requested test point. Black meter lead to ground.

We are checking if the DC adapter voltage is reaching this (+3VALW) regulator and also if the regulator is being ENABLED = told to turn ON or not.


2) Then repeat the same test for the +5VALW rail.

[mcplslg123]

Re: ACLU2 (G50-70) Motherboard Not Powering On

@mon2, is there any sense in measuring voltage at PU904 when it is clear from PQ302 measurements that B+ rail is absent.PQ301 is just passing the voltage in diode mode as there is no proper biasing at gate of PQ301. PQ304 & PQ305 are there for protection purpose.@Orestes, try removing PQ304 and PQ305 one at a time and see if you get 6V approx at pin4 of PQ301 or not??

ps: You can safely apply power while PQ304 & PQ305 is removed.

[orestes_]

Re: ACLU2 (G50-70) Motherboard Not Powering On

hi.

1) see attached. check and post the voltages at '1' and then for '2' on PU904.

Meter in DC mode (20v or higher is ok).

Red meter at the requested test point. Black meter lead to ground.

We are checking if the DC adapter voltage is reaching this (+3VALW) regulator and also if the regulator is being ENABLED = told to turn ON or not.


2) Then repeat the same test for the +5VALW rail.

Hello,

Thank you for your reply.

1)
1. No voltage

2)
1. No voltage

As for the other two points (for the 3V and 5V), I am not sure where exactly I should be probing for voltage? I tried probing both sides of all nearby passive components but I did not detect any voltage on all of them.

@mon2, is there any sense in measuring voltage at PU904 when it is clear from PQ302 measurements that B+ rail is absent.PQ301 is just passing the voltage in diode mode as there is no proper biasing at gate of PQ301. PQ304 & PQ305 are there for protection purpose.@Orestes, try removing PQ304 and PQ305 one at a time and see if you get 6V approx at pin4 of PQ301 or not??

ps: You can safely apply power while PQ304 & PQ305 is removed.

I am not sure I will be able to desolder them safely/resolder them back on the board if needed? I only have a T12 chinese soldering iron availiable.

I am attaching pictures as well.

May I ask this: with the information I have given you guys so far, what is your best guess as to what is the culprit? It is also making this repeating sound that you can hear in this video:

https://we.tl/t-DgEllpwkSF

(the background noise are the fans from my desktop computer. the sound that repeats every second or so is the one I am referring to).

Should I just buy a replacement motherboard from ebay/aliexpress for 80-90 euro and be done with it?

thanks.

[mcplslg123]

Re: ACLU2 (G50-70) Motherboard Not Powering On

Atleast give it a try. You wont loose anything as you're somewhat prepared to buy a replacement board. With a T12 iron and good amount of flux, you can remove PQ304/PQ305 though a hot air station would've helped a lot. This is not a tough fix and if you are not confident on your own, try some laptop repair shop nearby. that'll be a lot more reasonable and at fraction of replacement mb cost.

[orestes_]

Re: ACLU2 (G50-70) Motherboard Not Powering On

Atleast give it a try. You wont loose anything as you're somewhat prepared to buy a replacement board. With a T12 iron and good amount of flux, you can remove PQ304/PQ305 though a hot air station would've helped a lot. This is not a tough fix and if you are not confident on your own, try some laptop repair shop nearby. that'll be a lot more reasonable and at fraction of replacement mb cost.

are you suggesting removing these because they are possibly what's wrong with the motherboard or to further investigate what could be wrong with it?

[mcplslg123]

Re: ACLU2 (G50-70) Motherboard Not Powering On

You never know unless you remove those parts. Yes, my suggestion is to remove PQ304/305

[orestes_]

Re: ACLU2 (G50-70) Motherboard Not Powering On

You never know unless you remove those parts. Yes, my suggestion is to remove PQ304/305

i shall give it a try in the weekend then. I will keep you posted.

[orestes_]

Re: ACLU2 (G50-70) Motherboard Not Powering On

sorry guys for no updates, I haven't had any free time this past week to get to work on the motherboard..