determining the problem with power in my laptop - Page 1
Forum section: electronics / beginners

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 22, 2013, 06:54:14 pm
content: today my friend plugged my laptops PSU (19V at 11.6A) in the wrong way out as it is a 4 pin power din. unfortunately the connector is broken allowing it to be plugged in incorrectlyi am currently trying to determine what is broken to see if i can fix it myself as the laptop is out of warranty. fortunately my laptop does come with schematics but i am unsure what could have blown.on page 104 is the schematic for the input jack i have checked the first few components going into the laptop but the others are covered by the casing.I do think that its a fully isolated problem with just the input as the laptop is not turning on with the battery plugged in at all so i am thinking that it could have caused alot of other problems. The reason i have posted the schematic for the input is that i would like someone to check to see if there is any reverse polarity protection within the input to prevent this and if there is why it has failed.service manual

author: c4757p
author_rank: Super Contributor
timestamp: December 22, 2013, 08:22:39 pm
content: It looks like it has reverse polarity protection (PQ7, PQ49, PQ72 on page 104) for the main system, but it looks like a few of the parts of the power input section are not behind the protection. What do you see on the gates and sources of those transistors?Quote from: carbon dude oxide on December 22, 2013, 06:54:14 pmDon't dick around, tear it down completely. You'll need to.

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 22, 2013, 09:24:40 pm
content: Its an awkward laptop to take apart, i did before and it was a nightmare XDIm taking it apart now

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 22, 2013, 09:59:54 pm
content: I just tested PQ79, the source and drain were at 19V and gate was at 2.4V with the AC adapter inThe other two transistors are paralleled so i should not need to probe them should it?

author: ablacon64
author_rank: Frequent Contributor
timestamp: December 23, 2013, 01:31:21 am
content: Quote from: carbon dude oxide on December 22, 2013, 09:59:54 pmI guess you mean PQ72 ? It's ok. Check VA line (PQ38/PQ37 and so on).Most cases when this happens the battery charge IC gets shorted, in your case you should check OZ8681 (PU10).

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 23, 2013, 12:07:25 pm
content: Which pins on the OZ8581 do i need to check for shorts?

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 23, 2013, 12:51:40 pm
content: There is some fom or short when i plug both the AC adapter in or the battery, i can hear a small spark jump when i go to connect them, unfortunatly i dd try continuity testing the pins but there is no direct short accross the inputs.I have finaly foubd the OZ8681 battery charger an its a very small package no more than 4mm big in both directions, the pins are very close together and i am unsure if i can probe them with my multimetre, i may be able to get my scope onto it but that only measures voltageWhat should i do?

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 23, 2013, 12:59:19 pm
content: PR319 is measuring at 1.5K as opposed to 10k like the schematic says, and because its going from VA to ground could this be causing the problem? It is right at the input on the schematic its a nice 0201 resistor i belive

author: ablacon64
author_rank: Frequent Contributor
timestamp: December 23, 2013, 01:15:50 pm
content: Well, get a needle type probe or adapt yours. Does PU10 get hot when you plug ac adapter?Quote from: carbon dude oxide on December 23, 2013, 12:59:19 pmPR139 is a 0402, according to the schematics. Maybe.Have you checked PQ38/PQ37? You can remove PL14 to see what happens.

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 23, 2013, 01:20:53 pm
content: Il have to get my soldering iron outi did do a continuity test and resistance test over the inductor an it was a direct short over PL14. Surly it should have some resistance being an inductor?

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 23, 2013, 03:04:29 pm
content: The PU10 does not get hot wen i plug in the AC adaptor, should i still desolder PL14 its quite dence conponant wise around it and im affrade that i wont be able to take it off without messing the rest up

author: c4757p
author_rank: Super Contributor
timestamp: December 23, 2013, 03:11:26 pm
content: Quote from: carbon dude oxide on December 23, 2013, 12:59:19 pmPR319 is directly across the input. You're measuring the whole power input section in parallel with that. Make sure you are measuring it at a low test voltage that will not activate the P-N junctions of PQ72/49/7 and possibly PD21.Quote from: carbon dude oxide on December 23, 2013, 01:20:53 pmAn 8.2uH inductor in the power path? It probably has very little resistance. It's not failed, I think he just suggested taking it off to break the path through it and test the transistors which bridge that path.

author: amyk
author_rank: Super Contributor
timestamp: December 23, 2013, 03:37:52 pm
content: 1. What voltage do you get across PR319? (VA rail)2. What voltage do you get across PC264? (VA1 rail)3. What voltage do you get across PC78? (VREG5, 5V standby LDO rail)Let's just jump to the standby rails... actually in this model it looks like the main 3V3 and 5V rails are on all the time in standby, rather weird arrangement. Check for VDD3 across C404, C401, C4147, and C420.P.S. this is one of the best laptop service manuals I've ever seen... if only every one sold would come with documentation like this.

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 23, 2013, 03:42:45 pm
content: Quote from: amyk on December 23, 2013, 03:37:52 pmWith both battery and ac adapter pluged in or just the ac adapter?Its the best laptop ive had when its working

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 23, 2013, 06:02:40 pm
content: Ok i measured the votage accross all but 1 on the list, i coul not find PC78 on the board, ive spent quite a while searching and have only found PC76, i did also try to look for PU7 but i could not find that one either so i cant test te 5VREG unless there is another test point. The other two componants both showed a 19V accross them with the ac adaptor plugged in

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 23, 2013, 06:26:28 pm
content: PC78 was had practicaly 0V over it. I finaly found it im looking for the c4xx caps now

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 23, 2013, 06:37:44 pm
content: Ok summary:Voltge measured accross componantPR319 - 19VPC264 - 19V ishPC78 - 0vC404 - 0vC401 - 0vC417 - 0VC420 - 0vThis shows that my 5V and 3.3V rails are non existant right?

author: ablacon64
author_rank: Frequent Contributor
timestamp: December 23, 2013, 08:20:07 pm
content: Quote from: c4757p on December 23, 2013, 03:11:26 pmYes, it helps to determine where the short is.

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 23, 2013, 10:35:00 pm
content: How does removing that inductor help us find the problem? Surly if i remove it the smps wont work and i would still get no power?How would removing it teat the transistors?

author: amyk
author_rank: Super Contributor
timestamp: December 24, 2013, 12:45:31 pm
content: Quote from: carbon dude oxide on December 23, 2013, 06:37:44 pmSo you have VA and VA1 (i.e. PQ72,49,7 should be OK) but no LDO5 nor VDD3. I would then move to sheet 40 of the schematic where those voltages are generated by the buck converter UP6182 (incidentally, it looks to be a direct clone of the TPS51125, if you ever need to replace it - even thedatasheetlooks like a copy-paste job).Check voltages across these, they should be close to PU7 (the '6182):PR91 (master enable pin for the LDOs) - part might not be installed, just check the padsPC90 (LDO3, worth checking although nothing seems to use this rail)PR118 (3V3 enable pin)PR114 (5V enable pin)After a bit more looking through the schematic and datasheets I have a better understanding of the power system: 3.3V buck regulator is enabled all the time and powers most of the standby circuitry (including the EC), while 5V and the others are controlled by the EC (look at signals DD_ON and USB_CHARGE_EN).

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 24, 2013, 09:23:09 pm
content: Ok i just done some measurements and there is 380mv over the unpopulated PR91 pinsPC90 has 0V and PU7 itself has no power going into it over pins 15 and 16 (GND and VIN) so im going to search further down the VIN line to see if i can find faults. Datasheets on my phone dont work properly so it takes a while to find things T.T

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: December 24, 2013, 10:27:32 pm
content: U34 is a power controler and when the AC adapter is olugged in it heats up. Alot. U34 is responcible for producing the VIN1 voltage rail which ultimatly supplys the u6182 chip which supplys the 5v and 3.3v rails.Would you say that is is a sound judgment on what the problem could be as it takes power from both VA and VIN which both have 19V on them

author: amyk
author_rank: Super Contributor
timestamp: December 26, 2013, 12:35:29 pm
content: U34? Unfortunately I can't find any datasheet on the part (although there are plenty of sellers) but if it gets hot then either it's damaged or something on the rail it's connected to is.There's some rather interesting discussion in Russian site here about it though:QuoteMore seriously, I would probably try to replace it at this point, after removing it you can see if the VIN1/VIN is still shorted. It appears to be an integrated high-side switch with quite a high voltage rating, and I haven't been able to find any equivalents.

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: January 12, 2014, 08:09:50 am
content: Right i have soldered a new chip onto U34 and when i plugged te AC adaptor in the battery charging light and ac adaptor light turned on, however the laptop is still not turning on when i press the power button.I have had a look at what else is connected to the VA line and i can only find 3 capacitors all non polarised so they should be fine if there was a short. Does anyone else know what could also be the problem?