Hello, please forgive my not responding to you right away.
That meter is an older analog meter which uses a magnetic needle to display the reading. It is safe to use, but a bit more difficult to read compared to a digital LCD one.
The good point is, the needle is easier to see a visual response on compared to some digital ones.
The same rules apply here for a analog meter as a digital one, the RED probe is the POSITIVE probe and the BLACK is the NEGATIVE probe.
The configuration of those probes is mostly important when testing DC voltages. The scale on that meter tests both DC amperage (DC A) and DC Volts (DC V). The dial setting for DC power tests should be set to DC V. It appears your meter has a 50 VOLT setting, put the meter dial on the number 50, that's two clicks counter-clock-wise from OFF.
Now in the lower left corner of your meter are two holes marked - COM and + V The BLACK probe goes into the - Com and the RED goes into the +V
Now, have someone help you conduct the next test. If you have opened your laptop to expose the connector that power jack connects to the internal circuit board, per that video you posted Here's the link https://www.youtube.com/watch?v=HKs5Gtwzoso
you can test the RED wire and BLACK wire like that video shows.
Here is a picture for clarity You want to be careful not to allow those two probes to touch while doing this test, because I will be asking you to test a live DC circuit. If those two probes touch, you could cause a dead short and fry a component associated with your laptop.
While the laptop is powered by the AC power adapter, place the RED probe on the RED wire as per my photo above (Note the white connector with the RED, WHITE, BLACK, YELLOW wires going to it) and the BLACK probe on the BLACK wire. The meter's needle should move across the scale in the area of 18.5 volts. Analog meters are a bit difficult to read because each range has it's own scale across the meter's range. The black numbers can be either AC or DC reading numbers, where as AC on the scale is marked by RED lines across the scale. Confused? Don't be, I'll explain.
Look at the black numbers in the lower area of your meter, look for the range scale that goes from 0 to 50, that is the second scale range from the bottom. Notice it goes from 0 across to 50. That is the range you'll be looking at.
Now in that scale you'll see the number 20, that is the area that the needle should rest in when testing that circuit, that is 20 volts DC and your power adapter puts out roughly 18.5 Volts DC. So, that meter should be close to that area, if not a bit below that number. If it is way below that number like let's say 10, that is not good, it would mean your adapter is below it's power range. I doubt that will be the case though.
Now while the probes are on those wires, have an assistant mess around with the power plug and see if the needle responses when the plug is touched. If it does, it means one of two things, one the laptop power jack is defective or two, the adapter's power plug is bad.
To determine if it is the power plug and not the laptop's jack, you can test the adapter's plug by placing the two probes on the power plug while it is NOT plugged into the laptop. It is okay for the adapter to be plugged into the AC outlet and powered up though.
Keeping the meter in the same range, you would place the RED probe into the CENTER hole of the plug, and the BLACK probe on the outer exposed metal ring. Again DO NOT LET THOSE PROBES TOUCH EACH OTHER!!
The meter should respond and a reading close to 20 should be read. Now, move the wire just before it enters the plug, if the meter drops to zero and goes back to 20 again, you have a broken wire just before it enters the plug. This is caused by stress being put on the power plug when it is plugged in and unplugged.
There is a way to repair this problem very cheaply compared to replacing the laptop's power jack.
Please let me know what these two tests have proven and I'll advise you from there.If you have any questions, please do not hesitate to ask me first
Edited by MrBruce1959, 05 June 2015 - 12:33 PM.