HP laptop go-slow caused by power supply

Wasted some time recently looking at an HP Compaq NX7300 laptop, with Vista, that was running very slow.

No, not just normal Vista sluggishness. Really slow, as in you click the Start menu, wait a bit, and eventually it opens.

Temporarily disabled everything we could think of using msconfig (System Configuration Tool), still slow.

Checked the event log for disk errors, nothing wrong.

All very tedious as any actions took much longer than usual.

Found someone with the same problem on HP’s support forum here – but as so often with the Web, no solution is reported – though the guy does say, “can I assume that the cooling / cpu / power is defective”?

Called HP, and the guy diagnosed a faulty hard drive, though I was sceptical since his argument was that the self-test completed more quickly than expected, though it did not report any errors.

While scratching my head over this, I recalled that this laptop has what HP calls a “Smart AC Adapter”, which has an annoying proprietary connector featuring an additional central pin. According to this thread it actually supplies two separate power lines. The discussion includes this remark:

I tried to substitute the original HP AC adapter, with a general purpose AC adapter, applying a resistor divider between input cylinder- central pin-output cylinder, in order to get the second voltage.  But the laptop did not function normally: it was very slow

and someone adds

The slow function of the system with the alternative power source may be due to the system’s picking up a low voltage on the ‘monitoring’ pin.  This would indicate a low battery or weak charger and the system responded by cutting back on CPU/mainboard frequency to conserve power.

Could this be a clue? We started the laptop on battery power; suddenly it worked fine again. Plugged in the power cable, it slowed down. Removed the power cable, it speeded up again. Bingo.

New power supply is on order. It occurs to me that this could still be a problem with some internal connection, but I’ll be surprised if the new mains adapter does not fix it. Just occasionally the reason for a slow computer is nothing to do with Windows.

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169 thoughts on “HP laptop go-slow caused by power supply”

  1. i have 2 HP laptop, after 2 year both of them got this problem and the main cause of problem is their power adapter, as you know HP is generating very hot heat in the power supply system, this heat cause the power supply to damage itself and after 1-2 year , the problem got big and show itself to you.
    i tested a lot of things and find out that the problem is caused by the power.
    the test is this: run the laptop with the AC Adapter only and see if the problem exists, now run the Laptop with the fully charged Battery only and plug the AC Adapter out , if the problem goes and everything work great , the problem is caused by the Power Adapter.

  2. I have the same problem…at first when i experienced the problem,some friend of mine adviced to restore BOIS settings and save the changes. It only worked there and after a day i plugged the laptop in a deifferent adaptor and the same problem showed up again. I actually suspect the power supply like evryone says.

  3. I had the same problem on a HP nx6320 laptop running XP SP3. When on battery the CPU usage was less than 5% on logon but with the AC Adapter, the CPU would bump up to 100%. I quickly realized that Anti-virus software and the Task Manager (anywhere from 15 – 60%) were using almost 100% CPU. Initial suspects were botnets & rootkits as the AV usage was high. Did not find anything there. Next, I doubted whether the adapter the temperature of the motherboard to go up. I used CPUID’s Hardware monitor to look at the temperature of various on-board sensor’s. Most of them reported 102 – 140 degree F (40 – 60 deg Celsius) which is pretty normal. Swapping the battery of a colleague’s HP nx6320 also did not help. Finally swapped the AC Adapter and it worked like a charm. The CPU usage immediately dropped down to an avg. of 2% on no load.

  4. IS THIS HP’s way of selling Chargers. Is the charger programmed to go faulty after warranty period. This seems to be very frequent problem. HP should come out with customer information and replacements at its costs immediatly

  5. @Tom, #40:
    Thank you for your measurements! I had the same problem as most here – extremely slow operation and full CPU use with power cord connected, normal behavior with only battery.

    I measured my plug’s voltages and got pretty much the same voltages as Tom:

    “PS that slow Laptop
    19.85 V center pin
    19.85 V center ring”

    I opened up the plug and found the cord badly damaged. Also, the central pin and positive connector were bridged. I removed all the cords, cut it to get good cords, and soldered them back again. I then got these voltages:

    “PS that works good.
    19.44 V center pin
    20.01 V center ring”

    This solved my problem! The computer started up nicely and no problem whatsoever!

    If you are having this particular problem and have some know how in soldering, go ahead and try. It is possible that some of you have the problem on the mobo, but it’s always worth a try.

    Another possibility is to try another HP adapter. A third possibility (which I didn’t have a chance to test) is getting the docking station (I have a nx9420 which has this parcticular item) which has a 120W ac adapter.

    Hope you get your problem solved!


  6. I had the same problem with a HP Compaq 6710b. Ended up re-imaging 2 different laptops, resetting the bios and re-creating the users roaming profile, etc, etc. One one attempt to re-image, it took 7 hours to install windows!! lol. Swapped out the power supply and all works great – Thanks HP :-/

  7. Thank to this thread, i solved my HP nx7300 low performance problem. Laptop has finaly risen from 100% CPU usage to normal CPU usage and regular operating conditions.

    As considered earlier here, putting 47k resistor instead of HP’s default 10k resistor (between the inner ring conductor and center monitoring pin conductor) worked fine.

    On the other hand… everything in electronics is about compromise, and I wonder what are the consequences of lowering the center pin voltage in such great manner. For example, could that cause the battery not charging to an optimum value? Some questions are yet to be answered – hope someone finally reaches Hp. Good luck ~

  8. Finally!

    I had the problem – on battery only all worked well. Plug in the AC and it slowed to a crawl. This also meant that the battery was not charging. Change the AC supply and all is fast again.

  9. THANK YOU,THANK YOU. I have a HP Compaq Presario V6700 and it was so bad it took 15 minutes to open the browser. Then it would freeze. It was consuming 100% of the CPU. I bought new power supply yesterday and it instantly works so much better. Still have Vista and a hoggy virus software, but at least it is now usable. I don’t understand most of what you all said, but it was enough to save me from throwing this laptop out and gettin another.

  10. I had the exact same problem described by Tim with a Compaq 6910p. Vista was incredibly slow and the CPU was going 100%. I got the exact same message “smart AC adapter” problem. I disconnected the power supply from my laptop and immediately everything went back to normal!

  11. hi,
    im used compaq B1200 series laptop, recently my laptop performence slow while power up at the same time CPU shows 100%useage, run on battary perform excellent i checked and change new adoptor but problm on power up again, please give helping hand about my issue

  12. Having same problem right now with HP 6510b. Started seeing some issues with the charge now working correctly (battery not charging, sometimes wouldn’t show charge indicator when plugged in). Then yesterday CPU got bogged down – pegs at 100% and computer is slower than slow. Run on battery ok – plug it in WHAM dead slow. Plug that adapter into another HP computer same thing happens, use a good adapter on mine no issue.

  13. i have hp compaq presario cq61. when i unplug the charger the laptop is getting stuck. and when i use with batery power it is damn slow. my baterry is charging and some times it doesnt charge. when i roll on the battery icon it says not charging sometimes. what can i do.?

  14. hi,
    im used compaq B1200 series laptop, recently my laptop performence slow while power up at the same time CPU shows 100%useage, run on battary perform excellent i checked and change new adoptor but problm on power up again, please give helping hand about my issue

    i have the same problem.my compaq B1200 is so slow. when on battery it works fine but when i plugged it on AC it turns so slow that a simple alt+tab took 10seconds to appear..

    is buying a new ac adapter a solution to my problem?

  15. After almost a year I am still with the same problem, got a new AC adapter(this time original, not chineese),my laptop worked fine for three months, but again slow on power connection., so I think there is something more than the AC adapter.

  16. @Pedro so it worked OK with the new power supply for 3 months? If so, you could try returning the new power supply as faulty?


  17. I have the same problem with HP HDX16. After disable HP Wireless Assistant and set power policy to High Performance the problem goes away

  18. I have the same problem with my HP nc6320 the CPU jumps to 100% when the charger is connected and then drops instantly to 5% when I switch it off. Its also not charging the battery anymore.

    I did notice that there is a kink in the cable between the transformer and the connection to the laptop and by manipulating that I was able to find a spot when the cpu would drop and the battery would charge again.

    my next step would be to cut out the kink and see if I can salvage the charger without spending on another.

  19. Anybody who is struggling with this problem should do what amber0989 did. I thought my hard drive was finished when this problem occurred. I would have never though that the power supply would slow down my computer but when I accidental pulled out the ac adapter from the computer while loading a web browser I new it has something to do with the power. So I found this forum and after reading all comments I came to amber089’s solution and became very pleased when my computer ran at optimal speed.


  20. I own an HP Pavillion a1209n, and its about 4 years old, after a while it started running slow. I Did a total restore on it, wiped the hard drive twice and it worked better for a while, then It started Shutting itself off. No warning, Out of the blue. Never knew when it would do it and afterwards, Id have to wait 15 minutes and unplug the cord from the back before it would start up again normal. I did some research and found i could be the power supply so i took another compatible power supply out of my grandparents computer(they passed it on to me) and put it in my computer and all of a sudden my computer is running Faster! I did this about 3 hours ago and we will see if it shuts itself off again I hope not.

  21. I’ve had the same problem with my nx7400. My power supply arrived from Amazon this morning and it worked! Laptop now runs perfectly, with and without power supply!

  22. Thank you so much.I wasted so much time in figuring out what was wrong.. finally I got a answer with you guys. I replace the AC power adapter and the CPU is back to normal.
    Thanks Guys….

  23. Thank you! My adapter had the same issue, after attaching a new connector it started working fine. 🙂

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