HP DV6 Laptop not turning on - Fused mosfet? - Page 1
Forum section: electronics / repair

author: smanet
author_rank: Contributor
timestamp: June 24, 2016, 11:09:26 pm
content: First of all, I'm very new to this sort of repairs. I have done some very small electric repairs but nothing involving SMD.My wife's laptop is not turning on anymore after it went to sleep mode. I saw this is pretty common for Pavilion DV6.I have found a video on youtube that explains how to open it, mainly to clean up the dirty of the years and replace the thermal paste on GPU and CPU.So, after trying to disconnect everything, leaving only the motherboard and the power button attached, I have tried to turn it on without any luck.I was looking for burned/fused components all around the board without finding any.I have then decided to take off the heatsink and the fan.That operation reveled what I have identified as a fused MOSFET (I hope I'm describing it with the right terms!).It should be this one:https://www.fairchildsemi.com/products/discretes/fets/mosfets/FDMS7698.html.Could you please let me know if I'm right, having a look a the photos attached?I'm able to find spare parts of that component for around 4 pounds (for 10 pieces), however I'm without a soldering iron right now and I was wondering what would be the best for the job. So far, I have used only a normal solder.I believe SMD components will require extra care and special equipment, which I'm happy to buy if it can resolve this issue.Any advice for me?Thank you in advance

author: wraper
author_rank: Unknown
timestamp: June 24, 2016, 11:13:28 pm
content: You need hot air for this one. There is a thermal pad soldered to the PCB underneath, so you basically need to heat up the whole part to remove it or solder back. Probably doable with soldering iron, bet then you will need to preheat the board anyway, otherwise solder won't melt.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 25, 2016, 12:41:35 am
content: Meh, two irons with large chisel tips and flux and lots of solder. I've removed thermal pad parts like this, of course the part is dead after and you need the "touch" to not fry the pcb.

author: Monkeh
author_rank: Super Contributor
timestamp: June 25, 2016, 01:29:20 am
content: It's likely you can replace the whole board for similar cost to the tools required to have achanceof repairing it.I'm all for repair, but if you've never tackled this sort of task, you're probably better off replacing it.If, by remote chance, you happen to be in Cornwall, I have the tools.

author: smanet
author_rank: Contributor
timestamp: June 25, 2016, 11:55:42 am
content: Thank you all for the replies.I understand that it's a hell of job, but I'm wondering if Icando it on my own.I have found this on ebay:http://www.ebay.co.uk/itm/400778925552Would that be enough? And what temperature should I use to don't fry everything?Thank you again!

author: Monkeh
author_rank: Super Contributor
timestamp: June 25, 2016, 11:58:17 am
content: You'll need to get the part and copper under it up to around 220C, so you're not going to get anywhere with less than 350C aimed at it. Flux gel is also needed (I suppose you could get away with a flux pen, but gel is much better for these reflow times), which isn't cheap.

author: System Error Message
author_rank: Frequent Contributor
timestamp: June 25, 2016, 01:27:05 pm
content: before you start repairing see about discharging static by disconnecting all power and battery and holding the power button. Than start diagnosing the board and repairs.Some laptops are designed to fail within some years so find that component that is designed to fail and stop it working. If you think the mofset is fused which is also likely than try replacing it.Hot air guns are good for working on PCBs but make sure to cover other areas first. If you plan on repairing laptops commercially you will need a decent one.Louis Rossman has many videos on repairing various things, you ought to watch them. He also responds to PMs on youtube most of the time.

author: smanet
author_rank: Contributor
timestamp: June 25, 2016, 02:02:09 pm
content: Thank you again.I have tried to disconnect everything, even for an entire night. I have also remove the cmos battery without any luck.Last time it failed, less than a month ago, the laptop fried the hard drive PCB.I believe that the mosfet is fused, I have attached the photos to get advice if that could be a case.However, I believe they're not supposed to have a holeI don't plan to repair laptop commercially and, hopefully, this will be a one time only.That said, I have used soldering irons in the past and I'm happy to own one.Not sure if the one on the ebay link I have provided is decent though.I would love to hear any advice on how to cover the other areas (in fact I was wondering if I was going to de-solder too many things with the hot air gun!).I will try to watch as many tutorial as possible before proceed, I believe I will not have many chances to perform the same operation.

author: Monkeh
author_rank: Super Contributor
timestamp: June 25, 2016, 02:03:38 pm
content: You don't have to worry about desoldering things, they won't move unless you move them. You DO need to worry about plastic parts which may melt. To stop that you need to avoid the hot air hitting them. If there's nothing plastic nearby, you're fine, if there is, a simple piece of cardboard taped to the board to prevent the air making contact will be fine, it won't burst into flames.Again, for a one time repair, please examine the price of a replacement board and decide if it's worthwhile making the attempt.

author: amyk
author_rank: Super Contributor
timestamp: June 25, 2016, 06:41:35 pm
content: Hot air, definitely hot air.

author: smanet
author_rank: Contributor
timestamp: June 25, 2016, 06:46:16 pm
content: I was checking ebay for a spare motherboard and there only 4 and none in UK and only one in Europe.Anyway, no less than 60 pounds (excluding vat and import duties I guess).I know that it will fix it for sure, but I'm planning to keep to soldering iron and hot air for the futureNot sure on the quality of that one on Ebay though.So I guess I can give it a try.There's no plastic around the area, I'll watch some video to be sure that i'll try this right!.Thanks again for the great advises!

author: poot36
author_rank: Frequent Contributor
timestamp: June 27, 2016, 04:21:47 am
content: That is the VRM for the CPU if the mosfet failed it most likely took out the CPU by applying the full 19V of the power adapter to the CPU. Also this model is known for the video chip dying. I don't think this is worth it to try and repair. If you want to continue with the repair check all the other mosfets for shorts and also if possible check that mosfet driver is still working and is not also blown.

author: smanet
author_rank: Contributor
timestamp: June 28, 2016, 08:09:24 am
content: I hope that the CPU is still fine, I believe the mosfet failed gradually (if we can say that) as sometimes I was still be able to get some power light connecting the adapter.I wasn't aware of so many GPU failing with this model, however this one doesn't have a Nvidia chip but AMD.That said, it's the only mosfet I found in that state and I did look around the motherboard without finding any other blown element.I have ordered a soldering station (I didn't have one and it may be useful to me) and the part (10 mosfet for 5 pounds and few pence).If it works, great. If not, I still have my soldering station for another adventureThanks again for checking!

author: poot36
author_rank: Frequent Contributor
timestamp: June 29, 2016, 05:28:39 am
content: You may get away with removing the two mosfets the constitute 1 stage of the voltage regulator module (VRM) and it may still function. Depending on how badly damaged the mosfet is even hot air won't remove it due to it effectively welding itself to the copper trace below. Luckily yours does not look that burnt yet. If you remove the burnt looking one and the one beside it you will effectively disable one stage of the VRM and it should stay on if that was the only damage to the laptop. Or if you are lucky there may be a solder jumper that you can remove to completely remove power from the entire VRM and once again allow you to try to power on the laptop. I recommend a solder sucker or deslodering wick or brad for removing the solder jumper if the board has one. I just hope your soldering iron is at least 45W or more for removing the mosfet. I have seen a few AMD APU chips die just like the Nivida ones so you are not out of the woods yet.

author: smanet
author_rank: Contributor
timestamp: June 30, 2016, 08:33:45 am
content: Thank you all again for all the recommendations.With my new WEP 862D+, I was able to removed the burnt mosfet (I had to go up to 430C in order to remove it!) but I'm still not able to power on the laptop nor I see any light on when plugging in the power adapter.Yesterday I have double checked the power adapter on both the power jack itself and from the connector (disconnected from the motherboard) that goes into the motherboard and everything seems fine to me (more than 19V seen on the multimeter).However, when the connector is connected to the motherboard, I can see only very low voltages (in the order of 1.5/2V) and the two mosfet 4835d will became very hot.A google search revealed that they're most likely the major cause when a HP laptop (DV6 or DV7 series) doesn't turn on at all, as they may be shorted.I have a few questions:- How can I test them? I have found some directions on how to do that with the multimeter in both diode mode or resistance mode on Internet but I would love to hear from you too. Especially, should I take them off the motherboard for testing? This is should be the datasheet for the replacement parts too:http://pdf1.alldatasheet.com/datasheet-pdf/view/519768/VISHAY/SI4835DDY-T1-E3.html- What would be the best replacement part if one or more are failed? I can find "easily" them here:http://www.ebay.co.uk/itm/2-Unidad-SI4835DY-T1-E3-SI4835D-SI4835-4835-SOP8-100-Original-/172192029843?hash=item281771dc93:g:KsgAAOSwFqJWkpzkor on RS online (but I have to buy at least 20!).- I'm trying to understand what the other two mosfet 4134 are for and if I will need to check them.I have attached some images for reference.Thank you again for all your helpMuch appreciated

author: smanet
author_rank: Contributor
timestamp: June 30, 2016, 08:09:58 pm
content: Using instructions here:https://endless-sphere.com/forums/viewtopic.php?f=16&t=19645,it seems to me that both 4134 have failed, while 4835 look healthy.I'm happy to remove them to test them off circuit, just wanted to confirm if the tests are fine, especially the first one.I have used PIN 1 (S) and PIN 4 (G) and I got reads between 300 and 600.For 4835, I have just inverted the polarities for the first test and they showed open circuit (multimeter only displayed a 1).Another guide was this one:http://linuxehacking.ovh/2015/07/22/how-to-easily-test-n-channel-or-p/Any feedback is appreciated

author: poot36
author_rank: Frequent Contributor
timestamp: July 04, 2016, 01:56:39 am
content: If you get any reading from the gate to any of the other pins when the mosfet is out of circuit it is bad (unless your meter can supply enough voltage to turn on the mosfet). If you measure between the drain and source you should get no reading or a reading of the internal body diode depending on which way around the meter probes are. If you get any other readings the mosfet is bad.

author: smanet
author_rank: Contributor
timestamp: July 04, 2016, 09:15:39 am
content: Thank you poot36!I have followed all the guides and I have even taken off circuit the mosfet but they have all passed the tests.I'm investigating now the IC power controller TPS51125:http://www.ti.com/product/TPS51125and while checking the VIN pin, it should get 19V while I can see something fluctuating from 0.5 to 2.5.I was checking this russian forum (http://notebook1.ru/forma1/viewtopic.php?f=232&t=76663&start=0) talking about it. Google translator helpsI think I have found the schema of board here:https://gofile.io/?id=LidOQ4(I cannot attach it directly as it's 2 MB), but I didn't have time to give it a proper look and I'm also unsure if I will understand it properlyI was able to extract and add the pages relative to the charger, so they're attached here.

author: Monkeh
author_rank: Super Contributor
timestamp: July 04, 2016, 10:23:54 am
content: And now we play the hunting game.For a start, verify B+ itself does not have a short to ground somewhere.Seeing as PQ820 blew up, which is the high side FET of one stage of the CPU power regulator, money is on the fault being there. Remove PL807 to PL809 and check for a short to ground only on the FET side of them (the CPU probably will not appreciate your multimeter's voltage).E: Oh right, it's socketed. You can actually just pull the CPU to make these measurements and leave those big inductors alone. You may need to pull the FETs or cut the jumper at PJP822 to verify B+ doesn't have another fault.

author: smanet
author_rank: Contributor
timestamp: July 04, 2016, 05:23:32 pm
content: Thank you Monkeh.It would make sense to me that the power will not reach the cpu power modules until I turn on the laptop.Am I right in thinking that?This is the reason while I'm not concentrating the effort of the zone when the mosfet fused yet.I'll try to find a good ground to make all the reading of B+, but if you have any suggestion I will appreciate

author: Monkeh
author_rank: Super Contributor
timestamp: July 04, 2016, 05:26:13 pm
content: Quote from: smanet on July 04, 2016, 05:23:32 pmGenerally, yes.QuoteThis is the area in which violent damage occured. It is the most likely place to find further damage. Any of the other FET pairs could be damaged (and with them, the CPU). Clear the already suspect circuit before looking elsewhere.

author: smanet
author_rank: Contributor
timestamp: July 12, 2016, 08:54:15 pm
content: So I have removed the CPU and checked all the mosfet around the CPU power module but I couldn't find any suspect.Unfortunately jumper PJP822 doesn't exist on the motherboard!PQ812 and PQ813 are still getting very hot.Measurements on the connector (Pin 1 and 2), on PC850 and on PQ812 (Pin 3) showed a voltage between 0.5 and 2.15, which I guess it's not correct.Checked again the voltage of the power adapter and verified a 19.18V.If you think that I should concentrate my effort on the CPU power module, I will go ahead and take off pairs of mosfet and re-test.Do you have any good advise for me ?

author: mich41
author_rank: Regular Contributor
timestamp: July 13, 2016, 05:59:51 am
content: Did you check all VSTBY lines (and B+) for shorts to ground? I mean - black on ground, red on line, see what comes up in "200 Ohm" and "diode" ranges.

author: smanet
author_rank: Contributor
timestamp: July 13, 2016, 06:01:45 pm
content: I have tried that but I'm unsure if I have that correctly. Could you please point me some elements, based on the schema, where I should check the short for?I'm really sorry but I'm really a novice to this, willing to learn a lot with this experience.During my own tests, I got a possible short (diode mode showing 001.5 or less) between ground and pin 1/2/3 of PQ813 (one of the two mosfet which get insanely hot when the adapter power is applied to the board).Again, I'm not sure if I'm doing this right.Elsewhere I have read that hot components should mean that the component is broken, but I have tested them all.... I'm confused at this point

author: Monkeh
author_rank: Super Contributor
timestamp: July 13, 2016, 08:05:31 pm
content: Quote from: smanet on July 12, 2016, 08:54:15 pmThis indicates a short to ground. Neother PQ812 nor PQ813 can cause this. Either B+ directly or the output of a supply fed from B+ has a fault.According to the schematic and what pictures I can find with useful resolution, there are jumpers for isolating B+ from each rail. Find them, open them up (this will likely involve using a knife. Very, very carefully.), and go from there. PJP822 is the first one to try, for the CPU regulators. If you can't see it, remove the tape from the edge of the board.

author: mich41
author_rank: Regular Contributor
timestamp: July 14, 2016, 06:49:50 am
content: Quote from: smanet on July 13, 2016, 06:01:45 pmUse the schematic. Find any PCB trace, element pin or connector which is wired to the voltage rail you want. For B+, this might be pin 16 of PU9 or pins 5-8 of PQ809. For V5STBY, pins 1,2,3 of PQ809. For 3.3VSTBY some of the resistors near PSU input or PL806. I don't have the full schematic so you'll need to look yourself if there are other standby lines. All of them come up a soon as power is applied so any of them could be the one shorting all the current to ground.Quote from: smanet on July 13, 2016, 06:01:45 pmThis point is wired directly to 19VADP and to B+ through a 0.01 resistor, so there must be a short from 19VADP or B+ to ground. Most likely some component connected directly to 19VADP or B+ and to ground has an internal short (like PU9 or C1146, but ignore caps until you check ICs and transistors first). It's also possible that the short goes through multiple broken components in a row - for example PQ809 and PQ808 (just example, you said you checked those) or through the PQ811 transistor combo or through PQ811 and something on 3.3VSTBY. So even if we know there is short on B+, check for shorts on standby rails too.Quote from: smanet on July 13, 2016, 06:01:45 pmHot means there is excessive current flowing through them. This indeed could happen if they were connected to ground and internally fused, passing all current from adapter to ground. But they are neither internally shorted (at least you said so) nor connected to ground (the only path to ground goes through pin 4 and some resistors and resistors are probably the least likely parts to get shorted in 19V circuit). So they are getting hot because they pass PSU current onto B+ rail and something takes it from there to ground. This something is probably getting hot too, so go and check temperature of other things connected to B+ or 19VADP.EDIT:Oops, I missed Monkeh's reply on page 2. Sure, you can open those jumpers to disconnect things from B+ rail until the short is gone. But I'd start with looking for hot chips and transistors connected to B+. Then search schematic for "B+ -to- ground" transistor combos like PQ808,PQ809 or PQ811 or the CPU transistors where you started and check for shorts from between the two transistors (there should be a coil there) to ground. Those are switching voltage regulators, if you find a short on one's output you may avoid messing with jumpers.

author: smanet
author_rank: Contributor
timestamp: July 14, 2016, 08:38:30 am
content: Thank you Monkeh and mich41 for bearing with me! I really appreciate.I'll perform some additional test as mich41 pointed and check if there's any other element that becomes hot while the power is applied to the board.I would like to open the jumper as a last resort (I'm still trying to understand how to use the knife over there, my experience with jumpers on motherboards is a bit diverse!!)I have attached again the schema and full high resolution photos of the motherboard, your expert eyes may see what I can't!!Here is the link:https://gofile.io/?id=HbanaKPage 40 and 41 shows the charger and CPU power part.Thanks again!

author: Monkeh
author_rank: Super Contributor
timestamp: July 14, 2016, 11:42:21 am
content: Oh.. good.. they decided to ruin the jumper footprint on that revision so it's almost useless. Thank you, nameless chinese PCB manufacturer, may you rot in hell for all eternity.As mich41 said, now it's time to look for the other hot parts. Let it warm up for a few seconds and just run the back of your hand down the board. Wherever it feels warm, take a closer look. Again start around the CPU regs, and pretty much anything with an inductor near it. If those input PFETs are hot, something else is much hotter.

author: smanet
author_rank: Contributor
timestamp: July 17, 2016, 08:29:02 pm
content: Just an update: I didn't have time to follow all your advises yet, but I have left the board attached to the power adapter for a few seconds and PQ812 and PQ813 are hot as usual.But PQ802 is getting hotter than them both and I can't sense anything else getting hot near the CPU.However, this is in page 43 of the schema and it's in the other side of the CPU socket, in respect of where the other mosfet blown.As PQ802 is of the same kind of the mosfet blown and as I have other 9 as a spare, I will try to replace it.Or should I try to see if the board is alive without it?Of course I will follow mich41's advise as soon as I can to have a better idea if something else is failing here.Thanks!

author: Monkeh
author_rank: Super Contributor
timestamp: July 17, 2016, 08:36:33 pm
content: Yes, remove it and see if the rest of the rails come back to life. Do not install the CPU.One or both of PQ803 and PQ804 may also be at fault. PQ819 may well also be faulty, I don't recall if you checked that.

author: smanet
author_rank: Contributor
timestamp: July 17, 2016, 10:42:12 pm
content: Thanks Monkeh, I didn't inspect that side to the board yet.Searching for hot elements seems an "easier" way for me at this time, however I will inspect mosfet in that area too, hopefully tomorrow.Thank again for your help

author: mich41
author_rank: Regular Contributor
timestamp: July 18, 2016, 06:01:19 am
content: No PQ802 pin is connected to ground so something else in this area must be screwed as well. Probably transistors listed by Monkeh or PU802. Before removing this transistor, check for more hot parts. If you already removed it, check whether it's pin 4 or pins 1,2,3 that are shorted to ground by this unknown busted part.BTW, you said you have replacement for PQ802. Don't install it yet as it may blow up again if this other fault remains unfixed.

author: smanet
author_rank: Contributor
timestamp: July 18, 2016, 08:48:56 pm
content: So, no other mosfet nor the PU close to PQ802 were getting hot, only PQ802.The good news is that now, after removing it, I have got back my 19V everywhere, starting from the power socket connector to the TPS51125:http://www.ti.com/product/TPS51125.However, now TPS51125 is getting very hot. The VIN reports a good 18.80V input (even with battery I can see around 12V there), I can see Vreg3 with an output of around 3.90 (maybe too high?) but Vreg5 has only around 1.70/1.80 as output.I didn't replace PQ802 just yet, could be something I should do before blame IC power controller?Thanks!

author: Monkeh
author_rank: Super Contributor
timestamp: July 18, 2016, 09:01:50 pm
content: And on down the rabbithole we go.Nether LDO output is used for anything but the TPS51125, which is good.Check the external FETs (PQ808, 809, 811), it's possible one or more of them has broken down gate insulation.E: I have to ask.. what on earth did you do to the poor thing?The poor power supply is riddled with bullet holes!

author: smanet
author_rank: Contributor
timestamp: July 18, 2016, 10:14:45 pm
content: Quote from: Monkeh on July 18, 2016, 09:01:50 pmWell, it's what I'm trying to figure outI mean, it's not my laptop but I know my wife used to keep it running all day long so... it definitely had hard timesSo I will check PQ808, 809 and 811 between gate/source and gate/drain right? So for PQ811, let's say, pin 8 with pin 6 and then with pin 2. Also, pin 1 with pin 6 and then pin 2 again (at it has 2 gates from the schema)Meanwhile, should I replace PQ802?Thanks!

author: Monkeh
author_rank: Super Contributor
timestamp: July 18, 2016, 10:22:35 pm
content: Quote from: smanet on July 18, 2016, 10:14:45 pmWell, a closer look at the schematic and I can't see any attempt whatsoever to protect from ESD or other transients (there's whole papers on inrush transients with low ESR input capacitance etc, suffice it to say 'cables hurt'), so it's not too surprising. Schroedinger's laptop.QuoteThat's the ones. Also check m2 (that's underneath, so pick it up off the inductor) to both gates.QuoteOnly if you've verified the low side FET (PQ803, PQ804) has no short across or to the gate.

author: smanet
author_rank: Contributor
timestamp: July 18, 2016, 11:07:24 pm
content: I forgot that I have taken down PQ808 and PQ809 as I was getting strange readings when they were on the PCB and they were just fine.So I hope they are just fine, as I'm getting (again) strange reading between the gate and source/drain of PQ809.PQ811 will require a closer investigation as it's very small and I need to check it carefully, but from one first check, it seems alright to me.PQ803 and PQ804 don't look shorted, so I will try to replace PQ802 to see if there will be any change.I'm really trying here, I hope I can arrive to a point where something will start to work again

author: Monkeh
author_rank: Super Contributor
timestamp: July 18, 2016, 11:14:24 pm
content: Quote from: smanet on July 18, 2016, 11:07:24 pmYou might get odd readings on the high side gates in circuit due to the drivers.If all four (PQ811 being a dual) FETs appear intact then the TPS51125 itself is probably at fault. Try applying power without the FETs installed and see if the LDO rails come up normally.PQ802 being out won't bother this chip at all, without the rails PU9 generates, the CPU regulator will never get enabled.

author: Omegaman
author_rank: Contributor
timestamp: July 18, 2016, 11:57:24 pm
content: smanet: I would like to try and help you, if I can. I first want to say that it is best that you do not power the board up until you find and fix the issue. If you do, you may damage something else. I believe I have read all posts to date but if someone already suggested this then I apologize (I may have missed something).I do not believe your problem originates with B+. I believe others have mentioned this. Since PQ820 looks like it got very hot and melted a hole in it, you likely have a short of some kind on CPU_CORE (the signal, or net "CPU_CORE", which you should find in your schematic). You should check, with power off and no charger plugged in or main battery installed, with your ohm meter between PL808, Pin 2 and GND. You can check across PC92 (a cap, should be a rather large one to do this). You should not get anything close to zero ohms ( I am assuming you have the CPU removed from the socket here). Also, you need to check PL808 to GND (ohm meter across PQ819, Pin 19 & Pin 3), PQ822 the same pins, & PQ824 the same pins. With the CPU removed from its socket you should not get low resistance on any of these. The signals (nets) you are checking here for a short or low resistance to GND are - VREG_SW2_OUT, VREG_SW3_OUT, VREG_SW1_OUT, & CPU_CORE.If you can, please post the resistance values you measure on these four (4) signals/nets. Knowing these values may help to get closer to the root cause of your issue. I don't know what state your board is in right now, that is, what you have removed, have changed, ect., but if you would maybe you can let us know. I see you have been getting quite a number of suggestions from folks. There are some great people on here that can & will help you with your problem. I think to find the root cause of your problem it would be best if you have replaced PQ820 and put all other components (good ones of course) back on the board. It will be easier to troubleshoot if all components are back in place.Looking forward to your reply.Omegaman

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 12:10:42 am
content: Quote from: Omegaman on July 18, 2016, 11:57:24 pmApplying power to the board is the only way to determine where the issue is and whether it's fixed in many cases.QuoteThe fault around PQ820 seems to have been cleared, another one reared its head (PQ802, the high side for the graphics core buck) and has been cleared, and now a third device connected to B+ shows issues. I am still suspicious of the low side FETs, though, and confirming nothing further downstream (other than the CPU, which I suspect is toast) is damaged isn't a bad idea. I'd also point out that these are fairly robust chips and all sections of the CPU regulator have inductor current sensing and should have shut down long before PQ820 cooked that badly.A major transient on B+ via the AC adapter seems the likely cause.

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 12:22:01 am
content: smanet: I wanted to make a couple of other comments here that may be of some help.1) CPU_CORE, or one of the other three (3) signals I suggested you measure could be shorted to something other than GND, B+ for example. This short, however, may not be the root cause of your original problem as when PQ820 burnt up it likely shorted CPU_CORE to B+ through net CPU_PWR_SRC. Once you replaced this FET the short to B+ should have went away.2) With the CPU installed you will measure resistance to GND of CPU_CORE very low, probably about 1.5 ohms.3) PQ820 burning up could suggest the original problem may have been related to PQ821 and/or PQ823. This is because if, just as an example, one of these two had some issue then PQ820 would need to supply both its current and the current of the other FET or FETS, and this (if that happened) would cause more current to flow through PQ820 then it can handle. This FET can handle somewhere between 10 - 13 Amps Maximum.4) I believe you said that PJP822 is not on the board. This is a jumper so may not look like what you were looking for. It is not a chip but just a solid large bare wire, or could be just a trace that replaces the old part that used to be there in older revisions of the board.Omegaman

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 12:37:53 am
content: Monkeh: Thank you for the update. I was not sure just what had been done and what state the board is now in. I agree with you that these components are robust and there is considerable protection, such as over current protection, on these circuits. I also agree that the most likely cause of the original problem could very well be the AC Adapter, if it wasn't some kind of liquid found its way into the laptop. He probably would have found indications of liquid inside I would think.Although it is true at some point powering it up and checking voltages becomes the only way to troubleshoot a problem like this, there is much that can be done without power with an ohm meter. I think all troubleshooting with an ohm meter that can be done should be done before troubleshooting with power on. Maybe he is at that point now, so I don't disagree with you just believe it is better to do what you can with an ohm meter first.Excess current should have cause the controller to shut off power, but, obviously for whatever reason it did not or could not as PQ820 does look to be burnt up. Not sure what that tells us, if anything at all useful.Thanks again for updating me on the progress that has been made on this issue. Sounds like you guys are making good progress.Omegaman

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 12:50:35 am
content: Quote from: Omegaman on July 19, 2016, 12:37:53 amMost likely that the fault current went through the low side FET (for both this regulator and the failed GFX regulator) either due to breakdown of the high side FET during a low side on period or breakdown of both FETs in a row. The extent of damage across multiple circuits suggests overvoltage breakdown as the culprit. I've blown a few synchonous bucks up this way before with negligable load present.E: It may also have dumped straight through the CPU, once the high side's short all bets are off, eventually the load side of that inductor's going to get hairy.

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 01:16:51 am
content: Monkeh: I agree. It seems like there likely was some kind of transient or multiple high transients on B+, causing the original problem. Did he say anything about a power outage when or just before his problem first happened?I think the problems he is now chasing could have been caused by PQ820 when it shorted out B+ (18V or so) to many other different components. I also agree that the CPU would be highly in question, if CPU_CORE ended up with B+ on it. Unfortunately, most major power planes and some ICs are sourced by B+, which means this may be a difficult problem, set of problems, for smanet to find and fix if this theory is correct.Omegaman

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 01:27:30 am
content: Quote from: Omegaman on July 19, 2016, 01:16:51 amNo, nothing in particular, but if somehow the soft start circuit didn't function, merely plugging the adapter in can generate a transient of 2-3x supply voltage. They took no real steps to protect against that in the design as far as I can tell. Accident waiting to happen.QuoteEspecially as there are no jumpers to isolate things, they appear to have been replaced by mere silkscreen outlines. Right now we've got no power rails at all (PU9 providing the permanent +5V and +3V3 rails is not up with an apparent fault on its 5V LDO, looking like it's internal to the chip, it drives only that IC and the external gates). No other apparent shorts on B+, so the other supplies may be alright, but they won't come up without the 3V3 rail anyway. Just hope they, and all their downstream components, were protected by the CPU regulator's brave sacrifice..It's quite the rabbithole to go down, but that's the way of it. Great learning experience, though.

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 03:40:35 am
content: Yes, a true learning experience for sure. If I understood your previous post, I am assuming that B+ is up? You did not say if it is working or not but did say you did not think there was any more shorts. Boy, that is good news!The parts 5VLDO, "LDO5", is only used to power the charge LED (if it is turned on), and two (2) pins on PU9. TONSEL (pin 4) which sets the freq, and SKIPSEL (pin 14) which sets the operation mode - if LDO5 is on then OOA mode, and if off (pin is low) PWM mode. Neither should prevent the two (2) standby voltages 5VSTBY and 3.3VSTBY from coming on.EN0, PU9, pin 13 is the global enable for these two (2) powers. Have you happened to look at PR82, a 620K resistor? This resistor enables these two (2) powers and then ENTRIP1 (PU9, pin 1), and ENTRIP2 (PU9, pin 6) turn on 5VSTBY & 3.3VSTDY respectively. These active high signals (ENTRIP1 on PR834, & ENTRIP2 on PR89) set the threshold for RDSon. If low each will disable its standby power.Since EN0 disables ALL circuits, it might be worth looking at.Good luck.Omegaman

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 03:54:17 am
content: Quote from: Omegaman on July 19, 2016, 03:40:35 amAs of his last few posts, B+ is up to normal ~19V, indicating the shorts on it are cleared, but no other rails will ever come alive until +3.3VSTBY is restored.QuoteThe 5V LDO is used internally to power the chip and drive the external MOSFET gates, hence the large capacitor required on the output. No +5V, no gate drive, no standby rails.QuoteIf EN0 were tied to ground the LDOs would be at 0V, instead we're seeing 3.9V on LDO3 and <2V on LDO5. The very high 3.3V rail is worrying, and the low value on LDO5 and the very hot chip suggest thermal limiting due to overcurrent.

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 04:15:11 am
content: Sounds like some progress. Yes, LDO5 is used for internal analog & gate drivers.When you said there were no power rails I thought they were zero. Yes, it sounds like over-current. That 3.9 on 3.3V is not good at all. The less than 2V on 5V almost certainly is a current problem. When you say hot chip, is it PU9 or one of the FETs?Hopefully more progress will be made tomorrow.Omegaman

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 06:07:41 am
content: smanet, Monkeh, and all others. After doing some thinking on this problem here are some thoughts. I am just pretty much thinking out loud here and hope that maybe something here might be of some help to smanet. The step-down controller, PU9 (TPS51125RGER) may be bad at this point, but maybe something below will help to determine that.1) My understanding is that 5VSTBY is approximately 1.8V & 3.3VSTDY is approximately 3.9V. B+ is now up, and is about 18V. The below is based on this understanding.2) If 5VSTBY was drawing more current than it should, then PU9 should shut off 5VSTBY. Both 5V_DH & 5V_DL should be low (measured at PQ809, pin 4 & PQ808, pin 4 respectively). The threshold voltage for this would be approximately 163mV, measured across PR834. When EN1 (signal on PR834, pin 1) goes below this threshold, if PU9 is working properly, it will shut off 5VSTBY.3) If 5VSTBY is under voltage by 60% of its target PU9 should shut off both 5VSTB & 3.3VSTB. 5VSTB is only 36% of 5VSTB target value. This should shut off both the top and bottom FETs of both, measured at PQ809, pin 4, PQ808, pin 4; PQ811, pin 8 & pin 1 respectively, i.e. 5VSTB high side FET, low side FET; 3.3VSTBY high side FET, & low side FET.4) If 3.3VSTBY is over-voltage enough, approximately 115% (3.3V x 1.15 = 3.79V), the top FET (PQ809) would shut off, measured at PQ809, pin 4 = 0V) and the bottom FET (PQ808) would turn on, measured at PQ808, pin 4 = 5V).5) You might measure VREF at PR77, pin 1 (resistor not populated). This should be 2.00V.It seems that there is a chance that PU9 is bad. There could instead be something pulling 3.3VSTB higher then it should be, but PU9 should have handled that. Then 5VSTBY is very low, so there is probably more to it. These measurements should help to determine if PU9 is bad. Hope this is of some help.Good luck!Omegaman

author: mich41
author_rank: Regular Contributor
timestamp: July 19, 2016, 06:12:00 am
content: Quote from: smanet on July 18, 2016, 11:07:24 pmDo you how the short circuit through PQ802 reached ground and why this isn't going to happen anymore?Quote from: Omegaman on July 19, 2016, 04:15:11 amI think he meant no standby lines, which are those switchers driven by PU9. LDOs are internal to the chip and they work, just wrong. Or at least Monkeh assumes that standby lines are down because of funky PU9 LDO5 voltage, actually smarnet didn't measure them or didn't share the results.As for CPU regulator, the desktop VRMs I've seen claimed to have overvoltage protection which turns on all low side switches if output rises above some 1.6V or so. There's a chance for CPU to survive high side breakdown it this protection works fast enough. And I presume that the low side also has chances to survive a transient shoot-through due to its higher current rating.Still, this short through PQ802 is suspicious - IMO there should be no sub-1Ohm path from PQ802 to ground with power off but it seems that one exists.So, smanet, what's going on in there? Are any pads under PQ802 shorted to ground? This seems unrelated to PU9, btw, we are fighting on two fronts here.

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 08:21:25 am
content: smanet: If you have PQ802 removed from the board, I would make the following 2 measurements.1) Measure across the pads of PQ802, say pin 5 to pin 1. You should get a high reading on your ohm meter.2) Measure both sides of PL802, pin 1 & pin 2 to B+, on either PJP804 pin 1 or FL1 pin 2 (this inductor is not populated). You should get a high reading on your resistance measurement.3) Measure both pins 1 & 2 to GND on PL802. Now this may be a problem for you. I don't know what kind of meter you have. The measurement you will get will be likely less than 10 ohm, even less than 5 ohm. If your meter can do it, zero it out first by touching the probes together and if your meter supports it zero it by pushing the button RES. Your meter may be labeled something else, or may not have this feature. If it doesn't, note the reading you get when the probes are shorted together. Subtract this reading from the reading you get when do the measurement.If these measurements check out, it is my opinion that it would be pretty safe to put your new PQ802 on the board. You did say you have 9 of them.You seem to be dealing with 2 different problems.1) Problem with VGFX_CORE, i.e., PQ802 getting hot. The above speaks to this problem.2) Problem with 5VSTBY, & 3.3VSTBY, controlled by PU9. Please see the last post on page 2 of this thread for some information on this problem.It is probably best to work on one of these at a time. You did not provide information as to if VGFX_CORE has any voltage on it (measurable on pin 2 of PL802). If it doesn't, or possibly if it does but is the wrong voltage, it is my opinion that you might be better off to work on the VGFX_CORE (PQ802) problem first and try and fix it first. The reason for this is that if you fix the other problem, number 2 above, depending on what is going on with number 1 above it may turn on VGFX_CORE and risk damaging something else in this circuit. So, this is why the measurements suggested, and why my opinion is you should work on number 1 above first.Good luck, and I hope we are helping.Omegaman

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 11:41:10 am
content: Quote from: Omegaman on July 19, 2016, 06:07:41 amNo, those are the voltages measured on the LDO outputs - if VREG5 (LDO5) is <2V, there is no way it's managing to drive the gates and bring up the main rails. The LDO outputs do not supply anything else on the system.Quote from: mich41 on July 19, 2016, 06:12:00 amIndeed, at such a low voltage I'm assuming it cannot drive the gates. Certainly not usefully.We're definitely tackling multiple faults, the entire power supply is swiss cheese.

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 05:28:06 pm
content: smanet: Hi, hope you are making progress. For the PU9 problem, the signal/net LDO5 (PU9, pin 17 - name of pin is VREG5) powers the internal analog circuits, and the external gate drives for the two switching supplies, 5VSTBY, & 3.3VSTBY and also does connect externally. It connects back to PU9 on pin 4 (TONSEL), and pin 14 (SKIPSEL). Please see my previous post on the function of these pins.LDO5 also connects to the battery connector - CN_ADP801, pin3 (signal name on connector is - CHG_LED#) through a 510 ohm resistor (PR862, pin 1 = LDO5, pin 2 = CHG_LED#). It also connects to PQ12, pin 3 through this same resistor. Finally, it connects to cap CB856.I don't know if you have both the battery and the AC adapter plugged in when you are making these measurements or not. If you haven't done so yet, try and power up with only the AC adapter only (no battery installed). I think the most beneficial thing you could do would be to measure the voltage across PR862 with the battery plugged in, since it should be simple, and with the battery unplugged, or whatever condition you are making these measurements under.Measuring the voltage drop (if any) across PR862 would allow you to calculate the current being drawn from LDO5 here. PU9 can supply a maximum of 100mA. Please note that even if LDO5 were shorted through this resistor, PR862, directly to GND (on the CHG_LED# side of the resistor), it would only draw 10mA from LDO5. If CHG_LED# were shorted to B+, it would draw 35mA from LDO5. Whatever is drawn through PR862, if any, would need to be added to the current for TONSEL, SKIPSEL (both should be very low, probably uA), and the gate drivers of the 2 standby switchers, likely considerably higher that the 2 just mentioned, but still in the low mA range. Likely only 2 of these will be on at any given time.What I am trying to do here is to help you determine if PU9 is bad and needs to be replaced or if the issues you are seeing on these 2 standby voltages could be caused by something external. Since these should be quick measurements, it is my opinion they are worth doing even if they do not reveal the cause.Good luck, and please let us know how it is going.OmegamanQuoteLDO5, which I believe smanet said he measured at 1.8V or so, and it does connect to other places on the board. Please see my comments to smanet above. Yes, LDO5 may not be able to drive the gates properly, but since there is some voltage being produced on it, it will try. The Gate-Source Threshold Voltage of the FETs, PQ808 & PQ809 is 1.8V typical and 1.2V minimum. So, yes it probably can drive the gates on LDO5. Just to be a little more complete, the Gate-Source Threshod Voltage of the other FET used for 3.3VSTBY is 2.3V typical and 1.0V minimum.What my intent here is, is to try and determine if PU9 is bad, or the issue is caused by some external source, before smanet changes PU9 (which seems to be bad). There may be no issue whatsoever with the things I have suggested to smanet, but since they should be pretty easy and quick, I think they would be worth doing. Sometimes surprising things are found where they are least expected.Thanks for your comment. It looks like you have gotten him quite a far along on his daunting task.Omegaman

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 05:40:13 pm
content: Connections though moderate value resistors merely for purposes of driving LEDs are highly unlikely to be a concern. Even if PQ12 were short, the current would be negligable, and PR862 is highly unlikely to have become lower in value!As far as ability to drive the gates, yes, it may reach the threshold - but the drivers will be held off at such a low voltage anyway. See the block diagram.

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 05:54:11 pm
content: smanet: Something I should have mentioned in my previous post is that you could do a continuity check on connector CN_ADP801. Using your ohm meter, with AC adapter removed and battery removed, check between pin 3 and pin 2 on this connector. You also could check between pin 3 and pin 6. You should not get a low impedance (resistance) reading with either measurement. You certainly should not read zero (0).What you are looking for here is if pin 3 is shorted to GND (through the 510 ohm resistor), or more importantly if pin 3 is shorted to pin 2 (B+), through the same 510 ohm resistor. I think pins 3 & 2 are next to each other on this connector. IF it were shorted to B+ through this resistor (PR862), then LDO5 would be drawing an extra 35mA from this supply, which has a maximum of 100mA drive capacity. This would not effect B+ at all, but could possibly cause an issue with PU9.I hope this may help. There may be nothing here, but since it should be fairly easy and quick, it cannot hurt and could possibly help.Omegaman

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 06:28:39 pm
content: QuoteYes, the LEDs are not the concern here. I provided the current draw through PR862 if there were a short to GND, in my post. If LDO5 is shorted to B+ through this 510 ohm resistor (at the connector, CN_ADP801, pin 3 to pin 2) then that could add an extra 32mA to 35mA approximately to LDO5, which has a maximum current capacity of 100mA. This is 1/3 its capability, and could effect the operation of PU9 depending on the current draw of the gate drivers (assuming 2 gate drivers could be on at the same time, one from each supply). I don't know if PU9 staggers in any way these 2 standby powers or not.As to the gate drive, please see page 2 of the FET, Si4134DY data sheet. As I mentioned in my post, the Gate-Source Threshold Voltage is 1.8V typical, and the minimum is 1.2V. So, during normal operation the gates of these FETs will be driven at 1.8V approximately. As far as I know, smanet has not measured the actual gate voltage on either of these FETs (PQ809 & PQ808), and I have not suggested this. My understanding is the values of 1.8V is on 5VSTBY and not the gate of either FET. So, we don't really know what voltage is on the gate of either FET is, and without a scope he most likely cannot measure it. Please correct me if I am incorrect.I mentioned your points in my post, and again the goal here is to try and eliminate an external cause of smanet's issues before he changes PU9. Since these measurements should be very easy and quick, it cannot hurt to make them, and there could be something there, or maybe not. The way to find out is to take the simple measurements.Thanks.Omegaman

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 06:47:08 pm
content: Quote from: Omegaman on July 19, 2016, 06:28:39 pmNo, they would be driven right up to the rails to turn them hard on.. Driving them just to the threshold would not work. Which is irrelevant, because if you check the block diagram for the TPS51125, you'll see it has a schmitt trigger set to keep the drivers off if VREG5 is too low.Neither switching section will be active, and there's no realistic path for enough current to pull VREG5 down that low externally to the chip. Excluding physical damage to the board which certainly does not appear to be present, and is not consistent with the symptoms across the board.

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 07:14:20 pm
content: Monkeh: Yes, you are correct and I agree with the gate drive level during normal operation. I should have said a minimum of 1.8V, but they will be driven much higher and closer to 5V. I sometimes say one thing in my head but write something a little different.QuoteHere, I agree and disagree. If a potential of 1/3 of the maximum current capacity of PU9 is not enough current to effect the operation of PU9, and PU9 is not functioning properly in my understanding, then I am not sure what is. If board damage is present or not, at the connector, is what the measurements I suggested would help to determine. Since we do not know what the original root cause of this issue is, we do not know for sure if there is board or connector damage. Board damage cannot always been seen just by using sight. It is consistent with the symptoms IF there were a short from 5VLDO (VREG5) to B+ at the connector, or anywhere else, in my opinion. It all keys on how much current the gate/gates drive there is. If enough more current is drawn from PU9 than it can handle, then it cannot be predicted what PU9 will do.My troubleshooting techniques, are to eliminate the simple things first, IF they have any chance of causing or having something to do with causing the problem I am working on. This is because, first it is simple and quick, and second, there have been many times when working on a problem one gets caught up on the more complex but more likely causes only to find out a few hours or days later, when they decide to check the simple but unlikely things that they find the cause of their problem. I worked on a problem once for some time and ignored an input to a chip because it just connected to a jumper to GND and the jumper was populated. This was many years ago. So, thinking this is not the cause because this input should be at GND level, I worked on more complex areas of the chip to try and find the cause. After some time I finally decide to, hey, just check that signal at the chip when the failure happens. It glitched up to over 2.5V and ended up being the cause of the problem. The reason for this was that the trace ran all the way across the board (about 16 inches long), and through most of that length next to a high speed signal which cross-talked on to this signal, which should have been connected directly to GND.So, from experience I have found eliminating the simple things, even if they are not the most likely cause, is very helpful and although they are not more then they are, when they are it sure saves a LOT of time.Thanks.Omegaman

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 07:19:42 pm
content: Quote from: Omegaman on July 19, 2016, 07:14:20 pmThe gate drivers will not be active due to the undervoltage lockout. If there were a fault to B+ it would be sourcing current to LDO5, not sinking, and the voltage would surely go much higher than 1.8V unless further breakdown occured inside the chip - in which case it's dead anyway.Anyway, this isn't making progress. smanet can decide how to proceed and let us know what he finds.

author: smanet
author_rank: Contributor
timestamp: July 19, 2016, 08:27:41 pm
content: QuoteI have set the multimeter to 200k, I'm getting something like 13 or 30 (depending on the probes polarity) and then straight to 0.QuoteI have set the multimeter to 200k, I'm getting something like 6.3 and then straight to 0.QuoteI'm getting around 2.6 from each side (I don't have the best multimeter but I'm going to borrow a good one soon).QuoteI have in plan to do that when I'm sure that I will not break anotherBetween Pin 1 and Pin 5 of PQ802, which is off now, I'm getting around 3 ohm from each direction.Doing the same test on PQ803 and PQ804, I'm getting around 1.7 (which would let me think my meter isn't the best, is it?).I have also to report something strange that happened during my last measurements. First of all, without changing anything to the PCB, I have provided power to the PCB and I have started to smell something that was way too hot (or even burning), but I cannot see anything on the board itself that looks like it's gone.That said, I was able to see the 19V for a while and now it's gone again.The funny note, at least for me, is that when I don't have the 19V on the connector, the led on the power jack is blinking (it looks like the board is in standby) and PQ808 and especially PQ809 are becoming really hot as I provide power.I don't know what to believe anymoreIf you like to bear me and ask me for more measurements, I'm happy to do them (please indicate what PIN to check so it will be simpler to me).Otherwise, I will understand youThank you all again

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 08:47:22 pm
content: Quote from: smanet on July 19, 2016, 08:27:41 pmPQ802 is, as we knew, shorted. Dispose of it, it will require replacement - later.Switch your meter to diode mode, this will ensure the correct polarity (some meters are reversed in resistance mode). With the positive lead on drain (pins 5 to 9 on all FETs on page 43) and negative on source (pins 1 to 3), you should read open circuit. Any part which displays a reading in this direction should be removed and the measurement made again on the component directly, if it again conducts, the FET has broken down and requires replacement. Do this for all FETs on page 43, and we'll go from there. Don't replace any components, just remove as needed.E: I should clarify that a reading of a volt or two in diode mode shouldn't be a concern - only low readings, half a volt or below, are really of interest. If the reading is climbing, you're charging a capacitor, that's not a problem.QuoteComponents can get extremely hot without looking like anything has happened - the epoxy the ICs are encapsulated in is very durable. PQ820 only made itself visible because an enormous amount of energy was dissipated at once.QuoteThis is due to the power supply shutting down and restarting due to the short.QuoteYou have a multitude of faults and they are going to be hard to track down.E: Please remove the coin cell while we're working to avoid any oopsies involving it.

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 09:35:46 pm
content: smanet: The best I can tell from your post the measurements you made look to be ok helped by the fact, as you clearly indicated, you did this measurement by swapping the probes and measuring again, however I do not know what you mean by "...and then straight to 0". You can change your meter down from 200K to the next lower setting, probably 20K and you will get a more accurate measurement. If you mean that when leaving your probes on you first measure the values you indicate but then it drops to zero while they are still connected, then you may be charging up something (cap, etc.) with your meter. I do not understand what you mean here so cannot say.I see that Monkeh has some suggestions for you so will let him help you with this as you getting suggestions from multiple people may just make things more confusing for you. I will just make one more comment that may help you to not change out FETs that may not be bad.Make sure when you do any measurements you make on the FETs on page 43 that the CPU is NOT installed. I believe you have it out, but just wanted to make sure you knew that. If it is in, you will measure a very low resistance, almost certainly below 5 ohms on the bottom FETs (those connected to GND on pins 1-3). This would cause you to unmistakably remove FETs that are not bad. This has nothing to do with the FETs and everything to do with the CPU, and these particular FETs cannot be measured in circuit reliably if the CPU is installed.Good luck!Omegaman

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 09:43:15 pm
content: Yes, do not make any measurements with the CPU fitted. Not only will it mess with them, but the open circuit voltage of the meter could damage it (if it's not already wrecked).

author: smanet
author_rank: Contributor
timestamp: July 19, 2016, 10:32:11 pm
content: Quote from: Omegaman on July 19, 2016, 09:35:46 pmYou're right, I can see just for a second the resistance and then the multi meter goes to 0, so most likely the multimeter is charging something.I don't mind to get help from more people, but I need clear directions or I will get lostAlso it's good to see diverse points of view.I have removed PQ809 and I have got back my 19V.I have tested it again with my multimeter and it seems to be shorted now.I have previously tested PQ808 and PQ809 by removing them from the board and, as far as I can tell, they were good, so definitely something bad happened here.I have kept PQ809 and I'm going to run another test tomorrow with a more professional multimeter, maybe the late times doesn't help me too.I will remove the battery and check all the mosfet on page 43.The CPU is not on the board since a while, so it should be safe if it's not already broken of coruse!Thank you all!

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 10:38:13 pm
content: Are you absolutely certain you put them back in the right orientation and with no solder shorts underneath?The specific meter is irrelevant, even the cheapest will work for this. Just use diode mode to be certain of polarity.

author: smanet
author_rank: Contributor
timestamp: July 19, 2016, 10:50:35 pm
content: Quote from: Monkeh on July 19, 2016, 10:38:13 pmYes, I have actually used the pictures taken and posted here to be sure they were exactly oriented in the same way.I didn't see any solder shorts underneath after removing it, if I will put it back, I'll make sure to double check everything again.By the way, my understanding is that if you have a short between 1 to 3 and from 5 to 8 it's not really relevant, as they're all attached together internally. Am I right in thinking this? So basically of course we don't want shorts between source and drain and as well between gate and source/drain.However, I'm not looking to mess up anything but to improve myself in soldering.I think I have the cheapest one and I can borrow a good one, so at least I get to compare.I'll update you all tomorrow

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2016, 11:07:24 pm
content: Quote from: smanet on July 19, 2016, 10:50:35 pmCorrect, 1-3 are common and 5-8 are common. You're looking for shorts between those groups. Remember if you probe source to drain you'll see a diode drop (something like 0.4 to 0.8V, possibly lower, but well above zero), that's normal. This is for N-channel FETs (which all these buck converter parts are, as far as I can see), P-channel like PQ812 and 813 are backwards - diode conducts from drain to source.

author: Omegaman
author_rank: Contributor
timestamp: July 19, 2016, 11:23:32 pm
content: smanet: Thank you for your response. I agree that clear communication is essential, especially when doing this kind of remote troubleshooting. I have tried to be very specific, giving specific reference designators (i.e PQ809) and the pin numbers. I don't think the problem is clarity in this particular case. Please let me explain.What I believe has happened to some degree here is that we are talking two different languages. By that, I am not referring to English versus Spanish or anything like that. What I mean is when someone who is just starting out with electronics, or anything else technical for that mater (I believe you said this is the first time you have done this), is communicating with a design engineer, they are often speaking a different language. This is NOT the fault of anybody, it is just design engineers, and probably most engineers, kind of have their own language. I think some examples will help to explain.Lets take the measurements you took on VREG5 & VREG3. These are the names inside the IC (PU9) assigned by the chip manufactures. Design engineers never, or almost never, use these names. Unfortunately, this caused me to incorrectly associate these with 5VSTBY & 3.3VSTBY instead of LDO5 & LDO3, and resulted, I am sure, in comments I made that did not make sense. Again, this is no ones fault, or if someone is to blame it is ME. I realized this at some point, but much later than I should have. I apologize for that.Design engineers refer to net names, or signal names if you prefer, and not the names inside the IC. You will notice in the schematic that almost no net name is the same as the name inside the IC. This is because the engineer assigns his/her own net names that make the most sense to them. Often, the names inside the IC do not make sense to the engineer for what they are using it for, and sometimes it has multiple functions, 4 or 5 or more with a long name inside the IC with / in between each name for each function, such as GPIO10/ICS1/AD2 and so on.So, it helps if you use the net/signal name (net name and signal name are the same thing). So for example, you measured VREG5 (which is connected on PU9, pin 17) you would say "I measured LDO5 across cap PC60". Because the designer here used their nomenclature for naming components, it helps to say what kind of component it is, cap, resistor, diode, etc. Most Engineering places have their own nomenclature, so this just helps to be clearer. A sudo-standard, quite often not followed, is this - U for digital IC, C for cap, R for resistor, D for diode, etc. Here they use PQ for FETs, PU for ICs, PC for caps, etc. If you are measuring across a 2 pin component, then you can simply say "I measured 1.8V across PC60". This is clear enough for the other person to find it if they have the schematic. If not, it helps to give the signal name as designers are often familiar with those, or can figure them out, and what the component is, cap, resistor, IC, etc.Please let me stress that this is NOT critical of anyone. It is just an explanation of a little of the language engineers speak, or things they are used to hearing. I will also be as specific as I can, but sometimes too much information can be confusing, such as saying "I measured LDO5, VREF5, PU9 pin 17 across PC60, pin 1 to 2". Just saying "I measured LDO5 across PC60", provides all the information needed.Let me know if you have any questions or something I can help you with. I suspect you will be a while checking all the FETs on page 43, so you probably don't need any more suggestions right now.Good luck as always.Omegaman

author: Monkeh
author_rank: Super Contributor
timestamp: July 28, 2016, 02:19:31 am
content: This thread's gone awfully quiet. Have you popped it?

author: poot36
author_rank: Frequent Contributor
timestamp: July 29, 2016, 03:53:58 am
content: Here in Canada you can buy that laptop for around $150 used. I don't think it is worth fixing judging by the fact that it already took out a hard drive and now this problem.

author: Jimzz
author_rank: Newbie
timestamp: September 04, 2016, 06:58:07 am
content: Even i have a same laptop with exact "laptop dead" situation. PQ812 & PQ813, PC807,PC808,PC809 overheats.Could someone send me the updated link to download the same schematic. existing link is broken. Thanks