Author Topic: Removing PCB burn (Read 21665 times)

stewmath · « **on:** December 04, 2011, 10:48:27 pm »

Hi all

I 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.

Psi · « **Reply #1 on:** December 04, 2011, 10:52:07 pm »

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.

stewmath · « **Reply #2 on:** December 04, 2011, 11:08:59 pm »

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?

Psi · « **Reply #3 on:** December 04, 2011, 11:13:40 pm »

if its just a burn 'mark' then yeah you should be able to clean it off with some isopropanol and a hard brush
But if its actually 'charred pcb' you will have to carefully scrape it off

stewmath · « **Reply #4 on:** December 04, 2011, 11:23:58 pm »

cheers psi for the advice, i will give it a try.

hacklordsniper · « **Reply #5 on:** December 05, 2011, 05:57:32 am »

Maybe its just flux?

stewmath · « **Reply #6 on:** December 05, 2011, 09:08:23 pm »

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.

hacklordsniper · « **Reply #7 on:** December 05, 2011, 09:09:38 pm »

Quote from: stewmath on December 05, 2011, 09:08:23 pm

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.

Then that is surely flux from hand soldering. Dont fix what is not broken

stewmath · « **Reply #8 on:** December 05, 2011, 09:20:42 pm »

It is broken though, lol. pcb dont power up and no voltage getting to the board so im going to replace the jack.

hacklordsniper · « **Reply #9 on:** December 06, 2011, 06:51:09 am »

Quote from: stewmath on December 05, 2011, 09:20:42 pm

It is broken though, lol. pcb dont power up and no voltage getting to the board so im going to replace the jack.

Ups, 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).

stewmath · « **Reply #10 on:** December 06, 2011, 10:45:06 am »

I use flux pens, any idea if they need cleaning off. I clean them off anyway just to be sure.

joelby · « **Reply #11 on:** December 06, 2011, 12:32:41 pm »

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.

hacklordsniper · « **Reply #12 on:** December 06, 2011, 12:52:08 pm »

Quote from: stewmath on December 06, 2011, 10:45:06 am

I use flux pens, any idea if they need cleaning off. I clean them off anyway just to be sure.

I'm using a "no clean, water soluble flux". I don't clean it but if i need i don't need any special chemistry

stewmath · « **Reply #13 on:** December 06, 2011, 01:54:26 pm »

The one im currently is SMF12P flux pen, im not sure if its a no clean if im honest.

Fraser · « **Reply #14 on:** December 06, 2011, 08:44:46 pm »

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 conductive

You 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). Once all carbonised 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.

stewmath · « **Reply #15 on:** December 06, 2011, 08:50:53 pm »

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.

hacklordsniper · « **Reply #16 on:** December 07, 2011, 07:19:08 am »

Quote from: stewmath on December 06, 2011, 08:50:53 pm

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.

Probably you are facingg a connector soldered on both layers, be careful as its quite tricky compared to single layer desoldering

stewmath · « **Reply #17 on:** December 07, 2011, 09:03:05 am »

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.

hacklordsniper · « **Reply #18 on:** December 07, 2011, 10:30:04 am »

Quote from: stewmath on December 07, 2011, 09:03:05 am

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.

If 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).

stewmath · « **Reply #19 on:** December 07, 2011, 10:56:34 am »

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.

hacklordsniper · « **Reply #20 on:** December 07, 2011, 11:05:35 am »

Quote from: stewmath on December 07, 2011, 10:56:34 am

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.

The slowly break the connector and remove pin by pin. The heat the pin and remove it with tweezers

stewmath · « **Reply #21 on:** December 07, 2011, 11:09:44 am »

Quote

The slowly break the connector and remove pin by pin. The heat the pin and remove it with tweezers

Yeah 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.

stewmath · « **Reply #22 on:** December 07, 2011, 08:53:28 pm »

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.

hacklordsniper · « **Reply #23 on:** December 08, 2011, 09:09:47 am »

Sometimes this jacks can have multiple ground pins (maybe you are probbing them) and some charger have a third pin also

stewmath · « **Reply #24 on:** December 08, 2011, 09:29:48 am »

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.


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Author Topic: Removing PCB burn (Read 21665 times)

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