alienware 15 r3 (La-D751p) power issue

[Scotchmist]

I have this motherboard that will power on with the battery but give a battery not detected error

I thought one of the MOSFET had gone as I was getting 700 ohms resistance on one of 5 and showing 15v instead of the expected 19v - this made no difference.

I removed the battery and probed around, the mosfet is getting 19v but only 0.2v at the gate and source, the battery was giving me the 15v readings( lesson learned)

While the battery is disconnected the 3.3v and 5v is missing at the inductors - battery connected they are ok

Can anyone give me some advice on what to check - I have attached an image of the power input area and the voltages

Thank you

[mcplslg123]

Re: alienware 15 r3 (La-D751p) power issue

Give voltage readings of D-S-G pins of first two dc-in mosfets. measure them for short. Resistance on CLR?? Charger IC readings?? +19V is not passing thru as gate is not opening. The gate in turn is controlled by charging IC. So you need to diagnise accordingly.

[Scotchmist]

Re: alienware 15 r3 (La-D751p) power issue

Thanks for getting back to me

1st mosfet

D - 19.6v
S - starts at 0.4v drops to around 0.1v
G - same as S

2nd mosfet

D - 0.1v
S - 0.05v
G - 0v

On the underside of the board are identical pair of mosfet with the same readings

I have replaced all 4 but has made no difference

When I plug the battery in the 2nd two mosfet get 15v at D, 0.5 at g and s but the first two remain the same

when just on battery the sense pin gets 3.3v at the power connector but when I plug the power supply in the 3.3v goes to 0v

I have a second fully working board - I have checked around what I think is the charge ic (realtek ALC1309) resistance looks very silmilar

[mcplslg123]

Re: alienware 15 r3 (La-D751p) power issue

You have not answered me completely. What is the resistance on CLR?? That ALC1309 is not your charging ic but very likely audio chip.

[Scotchmist]

Re: alienware 15 r3 (La-D751p) power issue

Hi,

Resistance clr 0.1 - same on the working board

ALC1309 is the power ic, ALC3266 is the audio ic

I think I found the charge is AYOA 7317

All 4 Mosfet resistance s - g 47k ohms on bad motherboard
All 4 Mosfet resistance s - g 0.5 ohms on good motherboard

New mosfet out the board reads 0.5 ohms

There are a few different resistance readings near the AYOA ic

[piernov]

Re: alienware 15 r3 (La-D751p) power issue

ALC1309 is an audio amp. Nothing to do with charging circuit.

[Scotchmist]

Re: alienware 15 r3 (La-D751p) power issue

Sorry you are right it is an audio ic

My first Goole took me to eBay where it said power ic

[Scotchmist]

Re: alienware 15 r3 (La-D751p) power issue

Hi, I have replaced AYOA 7317 charge ic but made no difference.

Just the two MOSFETs at the start getting 19.6v but not opening

Does anyone have a schematic or board view?

Thanks

[SMDFlea]

Re: alienware 15 r3 (La-D751p) power issue

Hi, I have replaced AYOA 7317 charge ic but made no difference.

Just the two MOSFETs at the start getting 19.6v but not opening

Does anyone have a schematic or board view?

Thanks

Schematic requests go here - https://www.badcaps.net/forum/forumdisplay.php?f=41

The schematic is posted already. Try using the forum search - https://www.badcaps.net/forum/showth...light=La-D751p

[Scotchmist]

Re: alienware 15 r3 (La-D751p) power issue

Thanks SMDFlea, I was looking for Alienware r15 didn't realise it was the same board.

Found the issue BQ24780SRUYR was getting 19v in but nothing 0v on pin 1-5 - replaced this ic and all gates open

I will reassemble the laptop later today and let you know if everything is working correctly

[Scotchmist]

Re: alienware 15 r3 (La-D751p) power issue

I have assembled the laptop, battery seems to be charging, voltages look ok but now getting 2 red 1 blue fault

I was able to boot the laptop before. Think I need to disassemble and check everything is plugged in correctly.

[Scotchmist]

Re: alienware 15 r3 (La-D751p) power issue

The ic i used was from a Alienware 17r2 donor board that has the 7 beep issue which indicates a CPU fault and is usually not repairable- 2 red 1 blue on this is also a CPU fault - Now i think this ic could be the cause.

I will order a some new ic's and update when i have swapped it out. I could possibly get the 17r2 board working if this is true (only removed a few mosfets and the ic above)

[mcplslg123]

Re: alienware 15 r3 (La-D751p) power issue

7 beeps is very unlikely linked to BQ24780. This beeping fault may be somewhere else. First thing to do is bios flash with clean me.

[Scotchmist]

Re: alienware 15 r3 (La-D751p) power issue

Hi mcplslg123, on the 17r2 I reflashed the bios with clean me made no difference.

On this board you are correct, the BQ24780 has not caused the 1 blue 2 red issue I have now, I put a new one on.

I have good voltages on the AC and charge now but no CPU or GPU voltage

Must have been something I have done as it was booting but not charging, now charging and not booting.

Not sure where to go now

Thanks

[Scotchmist]

Re: alienware 15 r3 (La-D751p) power issue

I have probed all inductors on both the good and bad motherboard without battery installed and all voltages are similar.

Installed battery and pl700 is getting 19v one side and 6v on the other on the bad board. On the good board 15.6v both sides.

Probed around BQ24780 and found pin 4 had 24v and should be 19v

Checked the resistor pr708 and is ok at 4.12k
Checked mosfet pq701, pq702, pq707 and pq708 all have 19.6v d, 19.6v s and 24v g.

Hope this makes some sense, I am new to all this.

Thanks for all the help so far

[Scotchmist]

Re: alienware 15 r3 (La-D751p) power issue

Attached is a photo of the area with BQ24780

The two resistors should have 19v going to the capacitor above that has 0.4 ohms across, they then go onto the MOSFETs supplying 19v to the gate (I am guessing this is how it works - this is the voltage on the good motherboard)

On the bad motherboard one of the resistors has 24v going to the capacitor and it has 600 ohms across - one side has 19v the other 24v. 24v is then going to the gate on the mosfet