DC Jack spark

[bascotie]

Hi guys,

I fix computers for a living, but component level repair has always been something I felt I didn't know enough about, due to not knowing enough about testing electronic components.

In a more recent example that I'm trying to understand, i replaced a dc jack on a laptop motherboard. After quite some effort, I was able to remove the jack, remove enough of the solder to plug in the new jack, and solder it back in.

The laptop works, but when I plug the power adapter in 'hot' (when i plug the adapter into the outlet first, then the laptop), I get a small spark.

So I have a couple questions.

1) Since the problem is more immediate, how can I trace the cause of something like this down, and fix it? I did order another dc jack and am waiting on that, just in case it's the jack itself that's faulty.

2) For my line of work, is there a good electronics learning resource I can use to do my job better when it comes to component level repair?

Thanks!

 

[Harald Kapp]

1) The spark comes from the adapters output charging the laptop's internal capacitors almost instantaneously. Check the output voltage of the adapter when not connected to the laptop. Is it within the rated voltage? Some adapters may have an open circuit output voltage that is considerably higher than rated. The voltage will drop to nominal once the laptop is connected. A higher than nominal voltage may, however, damage the notebook. The manual for my notebook explicitely requires to plug in the adapter to the notebook first, then to the mains outlet. This is a good idea in your case, too.


2) Google 'basic electronics tutorial'

 

[bascotie]

1) The spark comes from the adapters output charging the laptop's internal capacitors almost instantaneously. Check the output voltage of the adapter when not connected to the laptop. Is it within the rated voltage? Some adapters may have an open circuit output voltage that is considerably higher than rated. The voltage will drop to nominal once the laptop is connected. A higher than nominal voltage may, however, damage the notebook. The manual for my notebook explicitely requires to plug in the adapter to the notebook first, then to the mains outlet. This is a good idea in your case, too.


2) Google 'basic electronics tutorial'

Thanks for the fast reply Harald.

It is a 19V 7.9 amp adapter, which is what this notebook uses (150W).

I also tried a 90W 18.5 adapter, which does turn it on and still sparks when plugging in the charger.

I was as careful as I could be while doing the job. Here's an image to give you an idea of what I was working around:

As for question 2, I guess I was hoping for a more 'specific' type of electronics knowledge to get a head start, so that I could move into this specific type of repair work more quickly. I'll have to start with the basics again after all

 

[shrtrnd]

I've got five HP laptops now.
The spark occurs when I plug them ALL into their power adapter.
I've tried plugging the DC plug in first, and then the AC power end, and I get the spark
at the power input!
I don't know why, Harald Kapp's explaination makes sense.
It's gotta be a design 'flaw', and doesn't interfere with the computer operation, so I just
live with it.
I suppose you can figure-out something to eliminate it, just wanted to say that I think
it's 'normal' for some systems.

 

[bascotie]

I've got five HP laptops now.
The spark occurs when I plug them ALL into their power adapter.
I've tried plugging the DC plug in first, and then the AC power end, and I get the spark
at the power input!
I don't know why, Harald Kapp's explaination makes sense.
It's gotta be a design 'flaw', and doesn't interfere with the computer operation, so I just
live with it.
I suppose you can figure-out something to eliminate it, just wanted to say that I think
it's 'normal' for some systems.

It looked pretty safe to me, considering it wasn't a big spark, and considering I see outlet plugs do it all the time.

The thing is, my customer in this case says it didn't do it before, so I think it's gonna be hard to convince him that it's normal, unfortunately.

Guess I should've stuck with software support

 

[shrtrnd]

I seriously doubt it just started happening.
Your customer probably just noticed it for the first time and got scared.
Good luck dealing with this.

 

[bascotie]

I seriously doubt it just started happening.
Your customer probably just noticed it for the first time and got scared.
Good luck dealing with this.

So there is no way it could be due to replacing the dc jack?

 

[Elecbegginner]

I would clean the surface with some PCB/flux cleaner , and do a nice soldering , and see what happens .

 

[bascotie]

thanks. will try that once the new jack comes in

 

[KrisBlueNZ]

It's normal. Most likely the customer just didn't notice it before.

It's common for people to notice things after a repair that they didn't notice before. When you buy something new, and it works, you don't look closely, but when it has been faulty (before AND after it has been repaired), you're naturally on the lookout for anything that seems unusual.

Sometimes after a repair, a customer will notice a problem that is totally unconnected to the repair and must have been present before the repair was made. It's just that their attitude to the device changes. Instead of assuming that everything is OK because it works, they're on the lookout for any signs of any problem.

BTW, don't expect Elecbegginner's suggestion to make any difference.

 

[bascotie]

thanks.

The thing is, I have seen plenty of laptops that do not spark when plugged in, including this same model. Not sure why it would decide to start now..

 

[(*steve*)]

I think you'd find that most laptops would spark a little as the power plug was inserted.

The only thing is, the outer sheath normally connects first, and the spark would be invisible inside the barrel of the connector as the centre pin makes contact.

What you seem to be seeing is a spark between the outside of the barrel and the laptop.

I could see this happening in some cases (including some fault cases) if the laptop was connected via (say) RS232 or USB to another mains powered appliance.

Is it connected to anything else?

 

[bascotie]

I think you'd find that most laptops would spark a little as the power plug was inserted.

The only thing is, the outer sheath normally connects first, and the spark would be invisible inside the barrel of the connector as the centre pin makes contact.

What you seem to be seeing is a spark between the outside of the barrel and the laptop.

I could see this happening in some cases (including some fault cases) if the laptop was connected via (say) RS232 or USB to another mains powered appliance.

Is it connected to anything else?

Not connected to anything else. I've also tested it with just the motherboard and power adapter out in the open. Good to hear that it's normal, just wish I could contain it so that sparks don't fly outwards

 

[KrisBlueNZ]

Good point Steve.

Whether the laptop is already externally grounded shouldn't make any difference because the power adapter's output is fully isolated, but the connector mating order will determine whether the spark occurs inside the plug or at the barrel.

The spark will occur at whichever contact mates last. If the original socket, in combination with that plug, mated the inner conductor last, the spark would have occured inside the plug and would have been less visible. Perhaps the new socket is constructed slightly differently - with the barrel contact in a slightly different place - and with that plug, the barrel connection mates last.

In either case a spark will occur and is nothing to worry about.

 

[bascotie]

thanks Kris, thats good to know