Removing PCB burn - Page 1
Forum section: electronics / beginners

author: stewmath
author_rank: Contributor
timestamp: December 04, 2011, 10:48:27 pm
content: Hi allI been dabbling with electronics on and off, but nothing major. Im looking at repairing the DC jack on my laptop and ive noticed some black burn around the solder joint from where it overheated. Is there a good way of removing this burn?Some of the components near it dont seem to be damaged so its just the jack that needs replacing.

author: Psi
author_rank: Super Contributor
timestamp: December 04, 2011, 10:52:07 pm
content: Depends how badly its burnt and how far down it goes.Sometimes if you try and scrape off the carbon you end up reaching one of the internal copper layers.

author: stewmath
author_rank: Contributor
timestamp: December 04, 2011, 11:08:59 pm
content: I was hoping not to scrape incase i damaged a track, is there any cleaning substance for pcb cleaning that can take this burn off the surface?

author: Psi
author_rank: Super Contributor
timestamp: December 04, 2011, 11:13:40 pm
content: if its just a burn 'mark' then yeah you should be able to clean it off with some isopropanol and a hard brushBut if its actually 'charred pcb' you will have to carefully scrape it off

author: stewmath
author_rank: Contributor
timestamp: December 04, 2011, 11:23:58 pm
content: cheers psi for the advice, i will give it a try.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 05, 2011, 05:57:32 am
content: Maybe its just flux?

author: stewmath
author_rank: Contributor
timestamp: December 05, 2011, 09:08:23 pm
content: I could possibly be flux, the laptop had previously been refurbished before i bought it as though its second hand, so they may have put some flux on.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 05, 2011, 09:09:38 pm
content: Quote from: stewmath on December 05, 2011, 09:08:23 pmThen that is surely flux from hand soldering. Dont fix what is not broken

author: stewmath
author_rank: Contributor
timestamp: December 05, 2011, 09:20:42 pm
content: It is broken though, lol. pcb dont power up and no voltage getting to the board so im going to replace the jack.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 06, 2011, 06:51:09 am
content: Quote from: stewmath on December 05, 2011, 09:20:42 pmUps, i missed that. After replacing the jack put a cotton stick in Alcohol and clean the remaining flux (or use flux which is not needed to be cleaned).

author: stewmath
author_rank: Contributor
timestamp: December 06, 2011, 10:45:06 am
content: I use flux pens, any idea if they need cleaning off. I clean them off anyway just to be sure.

author: joelby
author_rank: Frequent Contributor
timestamp: December 06, 2011, 12:32:41 pm
content: Is it a no clean flux? If so, you don't need to clean it. But it doesn't hurt if you do, especially if there's lots of residue left behind.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 06, 2011, 12:52:08 pm
content: Quote from: stewmath on December 06, 2011, 10:45:06 amI'm using a "no clean, water soluble flux". I don't clean it but if i need i don't need any special chemistry

author: stewmath
author_rank: Contributor
timestamp: December 06, 2011, 01:54:26 pm
content: The one im currently is SMF12P flux pen, im not sure if its a no clean if im honest.

author: Fraser
author_rank: Super Contributor
timestamp: December 06, 2011, 08:44:46 pm
content: Regarding the failed mainboard power connector....... have you carried out continuity checks on the PCB tracks and connector pins ? You could have a burn up on the PCB that has actually destroyed the connectivity between the PCB power plane and the connector plated through hole. I have seen this on high current power feeds and it can be a challenge to repair. The charring, if that is what it is, must be removed as it is conductiveYou need to carefully remove the power socket and inspect the condition of the plated through holes. Test continuity, then determine whether a new socket will actually solve your problem.Do not fear the PCB material. Carbonisation is very bad news and should be removed using either a scalpel (not ideal) or a 'Dremel' + small ball mill (preferred). Onceallcarbonised material is removed, the PCB may be inspected for damage properly and corrective action taken. When the inspection and and any repair work is completed, the 'crater' in the PCB may be filled with a non conductive epoxy and if you really wish to be professional, surface polished and then sealed with a suitable coloured PCB lacquer.

author: stewmath
author_rank: Contributor
timestamp: December 06, 2011, 08:50:53 pm
content: I will do the checks once ive managed to get the old jack off, i have a dreadful soldering iron which wont melt the old solder proper so looks like i need a better soldering iron.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 07, 2011, 07:19:08 am
content: Quote from: stewmath on December 06, 2011, 08:50:53 pmProbably you are facingg a connector soldered on both layers, be careful as its quite tricky compared to single layer desoldering

author: stewmath
author_rank: Contributor
timestamp: December 07, 2011, 09:03:05 am
content: I do have a friend that has a decent solder vacuum pump and a hot air reflow station, maybe if i use a small tip nozzle i can direct the air over each pin (one at a time, and suck the solder out)or just aim the air at all 3 pins and try and pull it out with some pliers.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 07, 2011, 10:30:04 am
content: Quote from: stewmath on December 07, 2011, 09:03:05 amIf i have a replacement and i dont care about the part im desoldering i break the part with cutters and remove pin by pin (if its a doublesided board, in singlesided i just vacum the solder out.Sucking the solder can be tricky on double sided boards, can you heat all pins at once with soldering iron? I dont reccomend using a hot air if you are inexperienced or you could blow away quite alot of SMD parts near the jack (it happened to me when i was beginner too).

author: stewmath
author_rank: Contributor
timestamp: December 07, 2011, 10:56:34 am
content: hacklordsniper , im quiet fortunate to have used hot air and infrared at university so it might come back to me. But i think i will try your method of cutting the jack off because i have a replacement part so im not fussed about breaking the old one. The solder is on both sides so it is pretty tricky, especially when my soldering iron at the moment wont melt solder properly for some reason. Probably cuz its lead free solder and the soldering iron is a cheap one for £15 from maplins.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 07, 2011, 11:05:35 am
content: Quote from: stewmath on December 07, 2011, 10:56:34 amThe slowly break the connector and remove pin by pin. The heat the pin and remove it with tweezers

author: stewmath
author_rank: Contributor
timestamp: December 07, 2011, 11:09:44 am
content: QuoteYeah im going to try that later, will just have to leave the iron on the solder for ages before it will melt it, useless iron.Once its off, i can then clean the area, move any remaining burn on the surface and do a continuity check. Hopefully all will be ok to put the new dc jack on.

author: stewmath
author_rank: Contributor
timestamp: December 07, 2011, 08:53:28 pm
content: Well i managed to remove the old dc jack and cleaned up the board. I check the continuity and there must be a short in one of the inner layer tracks because every track beeps. im def sure its not meant to do that. lol. So no idea how to fix that.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 08, 2011, 09:09:47 am
content: Sometimes this jacks can have multiple ground pins (maybe you are probbing them) and some charger have a third pin also

author: stewmath
author_rank: Contributor
timestamp: December 08, 2011, 09:29:48 am
content: This one has 4 pins, so i tested each one. (1GND -> 2,3,4) (2GND -> 1,3,4) and so on. Beeps on every one, seems something is shorted somewhere but i cant see it on the board so it must be an inner track.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 08, 2011, 10:13:02 am
content: Quote from: stewmath on December 08, 2011, 09:29:48 amThat is verry unlikely probably there is something dead after the jack

author: stewmath
author_rank: Contributor
timestamp: December 08, 2011, 10:33:53 am
content: I soldered the new jack on anyway just to test to see what happened. Plugged it in and my laptop power adapter just shorts and turns itself off. I didnt mind trying this because my aparter has an auto turn off if theres a short or overload etc.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 08, 2011, 10:52:33 am
content: Quote from: stewmath on December 08, 2011, 10:33:53 amThats a great way to do more damage before you know where is the problem

author: stewmath
author_rank: Contributor
timestamp: December 08, 2011, 11:02:00 am
content: Would a broken component after the dc jack cause the dc jack to short though?

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 08, 2011, 11:41:59 am
content: Quote from: stewmath on December 08, 2011, 11:02:00 amIt surely does

author: Short Circuit
author_rank: Frequent Contributor
timestamp: December 08, 2011, 11:44:32 am
content: Yes, perhaps a fractured ceramic capacitor, or a broken TVS diode, or the fets from a synchronous DC/DC switcher.Usually hard to find. Sometimes you can find the problem by applying a low-voltage high current and check where things get hot,but that requires a reliable and rugged PSU, capable of delivering 10-20amps at <1V.

author: stewmath
author_rank: Contributor
timestamp: December 08, 2011, 12:16:11 pm
content: @Short CircuitAs you can imagine im still learning, i dont unfortunatly have a psu with those capabilities. Just a very good universal laptop adapter and a couple of decent multimeters.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 08, 2011, 01:59:34 pm
content: Quote from: Short Circuit on December 08, 2011, 11:44:32 amI would not suggest to try that. The problem can be much deeper than at the jack.Did you truy to remove all hardware from laptop (cd drive, memory...) and see what will happen?

author: stewmath
author_rank: Contributor
timestamp: December 08, 2011, 02:04:27 pm
content: @hacklordthe laptop wouldnt power up before, power jack used to smoke as soon as plugged in and then adapter blew up. Thats why im using the universal one with short and surge protection.All hardware is removed because laptop is in pieces and the motherboard is on my worktop.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: December 08, 2011, 02:51:20 pm
content: Then you have a problem in the motherboard. If you are lucky the problem will be close to the DC jack

author: stewmath
author_rank: Contributor
timestamp: December 08, 2011, 03:52:51 pm
content: hack, yeah hopefully its one of the components near the DC jack. I had to replace the DC jack because the old one was buggerd and all burnt around the pins.

author: Fraser
author_rank: Super Contributor
timestamp: December 08, 2011, 08:34:44 pm
content: Hi,My thoughts for your consideration....Power sockets on laptops are open to physical abuse and can break free of the motherboard. This is quite a common occurrence with heavy handed or careless users. It is worth carefully inspecting the area around the power socket as the sort of heating you describe is uncommon in good solder joints working at less than 60A ! I mention this because it would be a pity to fit the new socket before ensuring that all is well below itNow onto your fault. You stated that the meter buzzed across all socket pads... useful but please be aware that an Ohms reading can offer more information than the <20 Ohms buzzer. A physical short circuit is not likely between power plane and 0V unless the unit has been messed with at some point. A shorted component across said power and 0V rail is far more likely as has already been stated.In such a case I would normally break out my Polar Toneohm which is basically a smart milliohm meter that leads the user to the lowest impedance across the power rails and so to the shorted component. Unfortunately these are expensive and normal multimeter's will not do the same job. I have been thinking laterally for you in terms of basic physics.1. You could buy some freezer spray from Maplin (~GBP5) and spray it on the area of interest, say 10cm x 10cm around the power socket. Let it frost over, then apply power to the board from the laptop PSU. The short should cause a heating effect in the area causing the problem and also possibly on the feed tracks to it. The frost should rapidly disappear at those points and may assist you with tracing the fault. The problem will be if the laptop power supply goes into foldback and current limits to a level too low to cause any heating effect. You could also try putting the PCB in the freezer overnight and seeing if a frost forms when removed...that's free2. Buy a cheap Infra Red thermometer. I found some on ebay for around GBP10. These are like tiny single element thermal 'imagers' in that they 'see' heat and so you could apply power to the PCB and use the IR thermometer to trace over the surface of the PCB looking for an area of increased heat dissipation. This would hopefully be the location of the short as the PSU overcurrent current foldback will likely prevent the motherboard powering up to any extent and so little, if any IC activity will be generating heat.3. MK1 eyeball, bright light and a 5X or 10X loupe.... its free and can often spot areas of localised heating. With all the heat generated at the power socket I would expect some pcb lacquer discolouration at the location of the short. A time consuming search process but cheap !I still recommend very careful examination of the area directly under the power socket. If there was a dry solder joint, it could have caused localised heating that in turn damaged the PCB and interlayer insulation...causing a short circuit at the power input point on the PCB.Good luck.... it will be a challenge without the normal repair equipment for this type of fault.

author: stewmath
author_rank: Contributor
timestamp: December 08, 2011, 10:02:19 pm
content: Aurora, cheers for the help mate. I will try the freezer spray idea. Also my multimeter has a built in thermometer so that could be useful.I did inspect the area under the jack under a microscope and it looked fine, apart from the black surface burn which came off with pcb cleaner.