Laptop Motherboard issue

[Dan Platten]

Hi guys,
after some advice on a laptop motherboard issue. Laptop is actually my own I use for day to day work and take to client appointments etc. - Laptop was plugged in and charging at home, I was doing some work, went to have lunch and came back an hour later to find the laptop off, no leds on at all. Unplugged anything plugged into it, no change. Removed battery , no change. Removed HDD and RAM and still not even an LED on at all. Which has me thinking it could be either a DC Jack issue or MOBO problem... I have checked the following....

- The Power brick / charger - I have tried a spare but also tested both with Multi-meter - All ok getting 19.7v
- Tested the DC Jack is getting power. - all ok @ 19.7v
- tested the MOBO where the DC jack is connected (in photo you can see the cable that connects the dc jack to the MOBO I tested the pins) - All ok (getting 19.7v on MM)

I am fairly new to MOBO repairs having mainly focused on software support in the past. But I would like to have ago at fixing it if I can.

I did notice that there is something white on the board next to the "PL30". As I said, I am a noob with the MOBO repairs so any help would be appreciated.

 

[GTP]

That "white" stuff is the result of that rectangular chip PL302? exploding.
PM me and I can get it repaired for you.

 

[Dan Platten]

That "white" stuff is the result of that rectangular chip PL302? exploding.
PM me and I can get it repaired for you.

Thanks for the reply! I would like to have a crack at repairing it if possible. Or is it something that cant be done and the workbench? Can you shed any light on what pl302 is?

 

[GTP]

PL302? is the number next to the chip. I have no idea what that chip is though.
Just by the pattern of the white mark it looks as if it has come from that chip.

 

[coffee]

Your gonna probably need a schematic of the laptop. Go by the manufactuer and model of motherboard listed on the actual motherboard. It will be stenciled on the mb.

 

[Diggs]

I haven't seen anything explode on a board since the capacitors on Gigabyte motherboards years ago. (Cool industrial espionage story BTW.) Way back when the CMOS batteries also used to be soldered down and then leak.

 

[Krynn72]

The PL prefix generally is used for inductors. An inductor should have continuity through itself, so take your multimeter and check. If you do have continuity then I'd probe around for shorted capacitors (the brown rectangles with silver ends).

For future reference, here's a good site that lists prefixes that manufacturers use.
http://adiedkhazbook.blogspot.com/p/blog-page_4.html?m=1

 

[gadgetfixup]

PL1 and PL2 are probably the same value as PL302. They appear to be transient dissipation components. Protection components for the surges that happen when you plug in your charger and unplug it. I doubt you find an issue in this area but it's a good idea to check the voltages just to be sure. That white stuff is probably moisture that has baked to the board and not the result of a component defect. I would look closer at other chips particularly the sound and network ICs. I can't tell you how many completely dead boards we've fixed by removing a blown network or sound quad packs. Look for a bubble or chunk missing from the chips

We pulled that off a Gateway NE56R41U that would power on but no video. Pulled the chip and the laptop works perfectly with the exception the network port doesn't work.

Also check the voltage on the white wire as that's probably the voltage for the MOSFET trigger. Most charging blocks today have 3 voltages, ground, power and trigger (center pin). If you don't have trigger voltage your MOSFETs will stay in the off position and block the 19V to the main rail. Check the 8 leg chip and make sure you have your 19V on 7 legs and not just 3 with the battery removed.

 

[NYJimbo]

That "white" stuff is the result of that rectangular chip PL302? exploding.
PM me and I can get it repaired for you.

Looks more like residue from a spill/drip. The chips dont seem to show any damage.

PL30 looks like a coil, PL4,2,1 look more like ferrite chokes ?

Edit: look at the top of the photo: PBATT AND PQ702 shows the same residue. So I am calling "spill" or (for some reason) "shenanigans" .

 

[fincoder]

Looks like corrosion to me, probably from a liquid spill in the past. It appears to be affecting several components as well. Bin it.

 

[Dan Platten]

A big thanks to everyone who has given me advice on this issue.

PL1 and PL2 are probably the same value as PL302. They appear to be transient dissipation components. Protection components for the surges that happen when you plug in your charger and unplug it. I doubt you find an issue in this area but it's a good idea to check the voltages just to be sure. That white stuff is probably moisture that has baked to the board and not the result of a component defect. I would look closer at other chips particularly the sound and network ICs. I can't tell you how many completely dead boards we've fixed by removing a blown network or sound quad packs. Look for a bubble or chunk missing from the chipsView attachment 7194

We pulled that off a Gateway NE56R41U that would power on but no video. Pulled the chip and the laptop works perfectly with the exception the network port doesn't work.

Also check the voltage on the white wire as that's probably the voltage for the MOSFET trigger. Most charging blocks today have 3 voltages, ground, power and trigger (center pin). If you don't have trigger voltage your MOSFETs will stay in the off position and block the 19V to the main rail. Check the 8 leg chip and make sure you have your 19V on 7 legs and not just 3 with the battery removed.

Have had a good look at the chips including sound, ethernet etc, can't see anything like your photo unfortunately. Seems like most people agree with you that the white stuff is moisture that has baked on the board and not an exploding component. Still tinkering around with the board but I think at the end of the day I will just get a new laptop - overdue for one anyway so I am not that concerned about this one, more so interested in learnign more about MOBO repairs and how they work.

 

[wavey]

If you have access to an ultrasonic cleaner try that if not, an old toothbrush and some isopropyl alcohol might sort it as a last resort.

 

[coffee]

Im sorry, Have you even posted the make, model number off the actual motherboard. Could you also post a good hi-res pic of the full board?

The basic motherboard is going to have a series of "rails" which are basically power feeds to individual circuits that run things like the processor, USB, HD controller ect.. There are going to be a series of power rails and the voltages have to be verified on them. Then there is going to be a circuit that provides a smaller voltage around 3/4 volts approximately that is a "safety check" . If this circuit is active then the laptop will power up. Its a sanity check.

You cannot really just probe around and when you find no voltage then think "Ok, this is where the problem is - I have no power on this chip output". Because the chip or component powering up depends on getting a "OK" signal from another circuit that basically says "Its ok to power up". So, Your really going to need a schematic of the board to start with.

The white stuff is where someone spilled something and it got on the board.

At best, without a schematic you are going to have to start at power input and check where voltage drops. Then there is going to be quad chip somewhere on the board that handles "power up" on the laptop. It determines if its ok to give power to the necessary circuits in the board. Grab the chip model number and get the datasheet on it - if possible.

As per what that chip is (PL***) you can just desolder it from the board and check it with a meter. If its just two legs on the chip it very well could be an inductor.

Just remember that when looking for the schematic for the board you must go by what is stenciled on the board. It totally depends who made the board and what revision it is. Working with a schematic with the wrong revision number can be very frustrating. But if that is all you can get then you will have to keep that in mind and do your best to spot changes in circuit layout and design from one revision to another.

coffee

 

[Dan Platten]

Im sorry, Have you even posted the make, model number off the actual motherboard. Could you also post a good hi-res pic of the full board?

thanks for the reply and detailed info Coffee. It's an Dell inspiron 15 MOBO Model = vbw01 la-9982p. Will have a look for a schematic online tonight when I get home (will double check the revision # too). Appreciate the info you have provided - If I can get my hands on a schematic I will begin reading through and see what I come up with. Thanks again to everyone who has given me advice, this is why I love Technibble

 

[coffee]

I looked on ebay and that board is kinda pricey.

There are a couple of 8 leg ics up near the battery and power connectors. I would look those part numbers up and under power check for voltages and use the datasheets for reference. I couldnt find a schematic for dell at all.

I think most of the charge and power circuits are near the battery and power inputs. So, I would probably concentrate there. What really *ucks is if its a capacitor you will not be able to determine the exact replacement. But for capacitors if you come close you should be ok.

 

[Larry Sabo]

Will have a look for a schematic online tonight

Here's one, but it requires that you be registered on the badcaps.net forum to download it.

 

[NJW]

but it requires that you be registered on the badcaps.net forum

Which is not a bad thing to do, if you have an interest in component-level repair. Lots of experience on that forum, even if you only lurk there. A useful source of capacitors, too, especially in low volume.

 

[Dee]

If you want a crack at repairing this mobo, you will need to learn how motherboards work, the sequence that it does when power is applied (not when power button pressed) i.e there maybe be a charger circuit that will activate which may also provide power to another part that supplies always voltages, there are variants from board to board in how they power up. Learning this will take a bit of time to get use to as it is very complex electronic engineering. A lot of schematics do not provide start up sequence and so knowledge is needed, i.e am I getting RSMST? Need to know the basics of what the big chips do, i.e northbridge, southbridge, gpu etc, some of these are even combined in one to save on costs and energy. There are some youtube videos out there that do a pretty good job explaining this, would be a place I would recommend to start learning this, if this is just a one off then its really not worth the time energy, only if its something your interested in. Search 'power start up of laptop motherboard' in youtube. This is the only proper way of narrowing down where the problem lies, could be a faulty cap, or mosfet or a voltage reg, the fix is easy, finding the fault is the hard part and what takes up time. No power on a board could be a zillion things, needs to narrowed down.

 

[HCHTech]

look at the top of the photo: PBATT AND PQ702 shows the same residue. So I am calling "spill" or (for some reason) "shenanigans" .

Ahh - our old friend: Nanigans of the she variety!