How do you test a laptop power supply??

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rufunky · #1 Post by **rufunky** » Thu Nov 16, 2006 8:12 pm

Whats the best way to test a laptop power supply? I have a multimeter but I don't know how I would use this to test it.

#2 Post by **jdhurst** » Thu Nov 16, 2006 8:23 pm

You may be out of your depth (respectively said).

First, get the hardware maintenance manual, although I don't think that will shed much light.

Second, know that your power adapter puts out a constant, regulated and reasonably noise-free 16 Volts (or other voltage depending on the machine).

So then there is an input on the motherboard for the 16 Volts, and it will distribute that to the inverter (for high voltage) and the regulators (for low voltage).

But (big but), for the most power (connector and inverter aside) a power failure on the board probably requires replacing the board.

So taken altogether, a multimeter may tell you if the power brick is working (but I think you would have known that). Otherwise, it won't provide much value. If the connector is broken, the machine won't run; if the inverter is toast, there is no light for the display; otherwise, I don't think the remaining power failures can be independently repaired.
... JD Hurst

#3 Post by **Kyocera** » Thu Nov 16, 2006 8:26 pm

Put it on DC volts, if you have a stepped meter put the volts around 20 or higher, place one probe in the center hole of the plug that plugs in to the thinkpad and the other probe on the outer ring (sleeve) check the LCD for a voltage reading if there is a minus sign in front of the reading it means the probes are backwards, no biggie the reading is still close. You should get a voltage close to what is rated on the sticker on the power supply. You can test amps to if your MM is equipped with a plug in for measuring amps, usually a third place to plug in one of the probes designated with a number followed by "A".

rufunky · #4 Post by **rufunky** » Thu Nov 16, 2006 8:43 pm

Kyocera wrote:Put it on DC volts, if you have a stepped meter put the volts around 20 or higher, place one probe in the center hole of the plug that plugs in to the thinkpad and the other probe on the outer ring (sleeve) check the LCD for a voltage reading if there is a minus sign in front of the reading it means the probes are backwards, no biggie the reading is still close. You should get a voltage close to what is rated on the sticker on the power supply. You can test amps to if your MM is equipped with a plug in for measuring amps, usually a third place to plug in one of the probes.

actually it's on HPZV5000 I Guess I just automatically posted in here cause I have a T40

..

The problem is the Laptop shuts down for no reason. when you push down on the plug where it plugs into the laptop it stays on and will even stay on for a little bit after letting go.

I opened the laptop and checked for a broken solder on the main board were the adapter plugs in and all seems fine. I just tested the power brick voltage and it's reading at a steady 18.4 V and its rated at 18.5 V so that seems ok as well.

#5 Post by **Kyocera** » Thu Nov 16, 2006 8:58 pm

You may have what is known as a cold solder joint or possibly a crack around a trace on the board near where the terminal plug is. If you have a soldering iron you can reheat/melt the joints where the plug is, to in effect re-solder them. Just get the iron hot and touch it briefly to the solder joints already in place.

rufunky · #6 Post by **rufunky** » Fri Nov 17, 2006 2:24 am

Thanks Kyocera, I will have to completely pull the main board for this so I'm going to try a couple more things first. I will let you know the out come either way.

#7 Post by **Kyocera** » Fri Nov 17, 2006 6:50 pm

I found a great link here about soldering in general which may be helpful:

http://www.aaroncake.net/electronics/solder.htm

rufunky · #8 Post by **rufunky** » Fri Nov 17, 2006 8:42 pm

Great link.. Thanks

fcampbel · #9 Post by **fcampbel** » Sun Nov 19, 2006 9:41 pm

I had a power cord break where it enters the plug. The computer would be running fine, plugged in. Then, it woudl give the unplugged sound. Over time it became more and more frequent. I too looked for a broken solder point, finding none, I tried a different power adapter. It did not cause the same problems. When I cut open the plastic lengthwise and dissected the plug, I found that the braided ground wire was broken and twisted. there was evidence of sparking where the wires would brush against each other. Enough of the small bare wires would touch to make it appear that everything was operating normally and then, without warning, the power would stop.

christopher_wolf · #10 Post by **christopher_wolf** » Sun Nov 19, 2006 9:48 pm

fcampbel wrote:I had a power cord break where it enters the plug. The computer would be running fine, plugged in. Then, it woudl give the unplugged sound. Over time it became more and more frequent. I too looked for a broken solder point, finding none, I tried a different power adapter. It did not cause the same problems. When I cut open the plastic lengthwise and dissected the plug, I found that the braided ground wire was broken and twisted. there was evidence of sparking where the wires would brush against each other. Enough of the small bare wires would touch to make it appear that everything was operating normally and then, without warning, the power would stop.

I had that happen on an old HP OmniBook of mine, just about the same thing. I did manage to get it fixed and it worked, but I was always careful about leaving the plug root in a bent position for an extended period of time.

fcampbel · #11 Post by **fcampbel** » Sun Nov 19, 2006 10:16 pm

I could use an extra power supply. I got a replacement tip from Radioshack but it seemed much less robust than the original and I started worrying about whether they were made to handle the current. I wouldn't want them to start heating up in there. Besides, I'm not very good at soldering. I always melt the plastics in the plug before I get the wire attached. I tried a couple of times and then ran into the filter magnet. If I try again, I'll have to cut off the magnet. If I can figure out how, I can get it loose and move it farther down the cable. Do you know where to find the specs and sources for the plug for an A21p or T42p? And I think maybe my soldering iron tips are too big. Since you did it successfully, any advice for me?

christopher_wolf · #12 Post by **christopher_wolf** » Sun Nov 19, 2006 10:54 pm

I had to use a pretty fine tip, 1mm I think, to get through and very carefully soldered it together. Originally, I didn't think that solder alone would do it, so I thought about inserting a tiny piece of fine wire, but it worked once I sealed everything back up tight enough. At the time, I didn't see anything much that was indicative of sparking.

I was glad I didn't have to get a replacement plug.

How do you test a laptop power supply??

How do you test a laptop power supply??

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