How do i Test a power jack with multimeter?

Posted on 2011-03-20
Last Modified: 2012-05-11
I need specific information on how to use a multimeter to test power on a HP DV6500 Laptop power jack.  

I have opened the laptop.
I have a multimeter with many settings.

What settings Do i need to have multimeter on?
Where do I place the multimeter prongs?
What "reading" will tell me it is working okay?

Thank you,
Question by:aacrz
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Accepted Solution

Reece Dodds earned 250 total points
ID: 35177099
Are you testing the AC Adapter (charger) or the jack where the charger plugs in to on the laptop itself??

If you are testing the AC Adapter:
Multimeter set to DC +/- 20V.  
Red lead touches (VERY CAREFULLY) the centre pin.
Black lead touches the outside of the connector.

Author Comment

ID: 35177138
Reece, I am testing the power jack.
Thank you for the settings, but I am unable to touch anything from the inside, may need to take out the whole board, and perhaps touch connectors at the bottom.  

This laptop will not power on.
I have tried another charger, taken out the battery (don't have another battery), but it will not power on.

Expert Comment

by:Reece Dodds
ID: 35177173
ok.  it's likely that the dc in jack is faulty (the only way it can fault is if it's connection to the mainboard is severed (via dry solder joints or a proken pin).

If the dc in jack is not faulty, then the power regulation circuitry could be the problem. In which case, you'd have yourself a faulty mainboard.

Either situation, you will unfortunately get access to the mainboard.

What is the product number (P/N) of your laptop, I will try to find you a service manual.
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Author Comment

ID: 35177199
when i plug the laptop power jack, the ring led comes on. So possibly bad motherboard?

Expert Comment

by:Reece Dodds
ID: 35177252
download this
it may be slightly different for your model, but i think this manual covers all of the DV6500/6600/6700 variants.

It is looking to be mainboard
LVL 15

Assisted Solution

Perarduaadastra earned 250 total points
ID: 35177325
If you're wanting to test the jack on the motherboard of the laptop itself, then it's wise to make a visual inspection of the socket and its mounting before using a multimeter on it. Unfortunately, this usually means removing the motherboard from the chassis to obtain the required access.
I'm assuming that your laptop uses a centre pin positive, which seems to be the most common layout.

Laptop power jacks are frequently troublesome because they are so vulnerable to damage from the AC adapter plug being knocked while it is inserted into the jack. The first thing to look for is physical damage to the socket and to its connection on the board; it's not uncommon for there to be cracks in the prongs by which the socket is connected to the board, and such cracks are often very difficult to see.

Set your multimeter to test for continuity - many such meters have a setting that allows the instrument to generate a simple tone when continuity is present; if yours doesn't have this feature then set the resistance scale to its lowest range and then test for continuity between the contacts inside the socket and where the prongs come out on the underside of the board. There are often three connections between the socket and the board, and the middle one usually goes to the positive pin in the centre of the socket. The outer ones are usually ground (negative) and correspond to the contacts in the "walls" of the socket, so to speak. There should be continuity between each connection on the back of the board and its corresponding contact in the socket; if there isn't, then that's probably where the trouble is.

Also check the quality of the solder on the underside of the board where the socket pins come through - the solder should be smooth and shiny. If it's dull and frosted, or burnt in appearance, then you have a dry joint and therefore a poor connection that must be cleaned and re-soldered before it can be expected to work properly.

The fact that the ring LED comes on but the laptop doesn’t, is a bad sign and suggests that the power control circuitry is no longer fit for purpose, and that in turn makes it likely that the board will need to be replaced (as reecem27 has already suggested), but as you have to take the machine apart anyway to get this far then it seems reasonable to rule out physical damage before condemning the mainboard.
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Expert Comment

ID: 35178974

Expert Comment

ID: 35182069
If you want to test the output of your laptop power supply look at the transformer and see if there is an output voltage printed on it somewhere it should have an input of 220-110 VAC and the output should be in VDC. Look to see the plug orientation. It should show pos or neg in the inside or outside of the plug. One you see how the plug is set up set your voltmeter for DC and in the range of your adapter put the neg lead on the neg side of the plug and pos on the pos on the pos side and you should get a reading close to the output printed on the transformer. This will tell you if your cord is putting out the correct voltage.
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Expert Comment

ID: 35182702
for most it is between18.5 and 20 V

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