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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167 comments to HP laptop go-slow caused by power supply

  • tom

    Had the same problem with hp probook, when on ac power it slows down to the point it is unusable but when on battery it runs fine. I have changed my default power settings to be the same when on battery and ac power and it seems to have solved the problem. Has the same fix worked with anyone else with the same issue or has it atleast alleviated the processor load. The charger seems to have something to do with it as well as it doesn’t charge the battery fast enough or could it be the battery that is going bad and causing it.
    Anyhow it is worth trying changing power setting options before buying a new charger or the battery.

  • AndrewID

    If the voltage of the center pin differs from 5V, the processor will run on 10% of its nominal performance.
    Check the connection of the center pin. If it shorted to the main supply line, it will behaves the same.
    Under load, you should measure 5V on the center, and 20V on the main supply (center ring) pin.

  • Do Kien

    I have the same problem with all of you. when I plug the adapter in, the battery not charging and also the CPU usage rise up to 100% and can’t running laptop. So I try to change my adapter by my friend adapter, my laptop become normal. In my conclusion, this problem cause adapter and need to change our adapter.

  • tom

    It is shorted. Is there a way to open up the adapter housing without destroying it. Is it casted plastic? I’ve chiped the edges trying to get it open.

  • jagath

    I had a same problem in my hp probook lap top,it is very slow when i connect the power adapter(processor usage going to 100%)but some time it’s working normally,in this time battery is not charging. when battery is charging processor going to 100%.I’m change power adapter but there is same problem……if u have any reason plz mail me ((((jagath8977@gmail.com)))

  • TR Colasanto

    This posting saved my sanity. If I hadn’t experienced this myself, I would never have believed anyone that told me this. I had the same exact symptoms with an HP Probook 6370b running Win7 Pro 64-bit. CPU pegged at 100% for no reason. Machine was not even usable. After reinstalling my OS and all drivers, I still had the same problem. It was only by accident I realized that when it was unplugged I didn’t have this problem. I stumbled upon this post, replaced the AC adapter, and all my problems were gone. Machine runs great now. It’s ridiculous that the machine throttles back because of this “smart” pin but gives no indication of what’s going on.

  • john

    Thanks for all the help everyone. I own a 6710b laptop and purchased a so-called genuine charger from ebay. It was a counterfeit and caused my computer to slow down also. In addition, it would not connect to the internet when using a Homeplug device. When I adjusted the laptop power option properties like recommended in previous posts it seemed to fix the slow down problem, but still would not connect to the internet. I ended up going to Staples and purchased a genuine HP charger that was on sale for $50 and that fixed all issues.

    I was curious about the voltage readings, so I measured both chargers. The fake one measured 19.47 – 19.51 volts on the center pin and 19.76 – 19.81 volts on the outer ring and for the real charger I got a steady 19.00 volts on the center pin and 19.55 volts on the outer ring.

  • Dan

    I have experienced the exactly some trouble at my daughter´s HP-Compaq 6710b – from time to time it ran very very slow, unusable for a work. After I had checked everything what I could check I noticed that the trouble never occur when the notebook is battery powered. Finally I found out that the cause was an ocasional short-circuit between the lead to the center pin and the +19V line inside the cable near its ending inside the adaptor. The cable has one central thin wire (control) – inner shielding (+19V) – outer shielding (GND).

  • I have a HP 8730w elitebook with the same problem. I tried everything when I read this post here. My laptop was extremely slow, not usable. I disconnected the powersupply and it works ok.
    I also went in here: http://h30434.www3.hp.com/t5/Notebook-Lockups-Freezes-Hangs/Win7-running-jittery-slow-for-no-reason-Hp-dv7/m-p/327927 and found a solution to test the speed using the dpc latency check. When I disconnected my power supply the DPC software showed normal behavior, when connected it showed bad behavior.
    I have just bought a new laptop because of this problem and realize that I only needed a new power supply.

  • houcinec

    le probleme c’est que le chargeur et en panne . les composant electronique de l’alimentation interne du pc et endommager (chargeur coup circuit) si tu demmarrer le pc avec le batterie seulement le pc et demmarrer sans aucun problem si tu poser dans l’alimentation le pc demmarer plus lent et ne fonction pas normalement. conclusion ( le probleme et materiel ) un cercuit de l’alimentation et endommager :)

  • Prabin

    I have Hp Probook 5330m Laptop when i connect charger my laptop get slow but there is no problem with batry i dont known what is the problem ??
    if anybody have idea about this please suggest me
    rockstarprabin@gmail.com

  • Waleran

    I had this problem with my HP 6320 laptop. 100% CPU when on AC power but OK when on battery. I bought a new power adaptor and plugged it in but it made no difference.

    So I checked the connection socket on the laptop and found that some of the pins inside were bent. I straightened these out and bingo, normal CPU % on AC power.

    There are 7 pins inside the power socket! Well done HP – a fragile interface inside one the most used sockets. There is an outer square of 4 pins, then an inner pair of two pins and then a central (or maybe slightly offset centrally) pin.

    So I don’t need a new laptop after all! Thanks to previous contributors for the initial solution.

  • This is your way if you wish to use replacement charger:
    Make voltage divider like mentioned before and aim getting 5,75V out to middle pin. You can get it work by using 10K and 4,7K resistors. This results 6,2V, which is close enough to fool your HP.

  • Romonus

    I all and every thing to speedup compaq 6510b Laptop nothing has helped, it just running like a buffalo cart. I think HP persons forgot to give importance to performance.

  • ellinor

    i got the amd version of nx6325.
    with a non stock power supply or the docking statiomn my notebook became very slow, even with linux running!
    i found out that the L2-cache got disabled when the middle-pin doesn’t supply at least 4V.
    the result is, that the system behaves just normal in bios, grub or memtest, but gets slow after leaving real-mode.

  • Aida noridania

    this topic saved me hours of searching. i had to check a HP notebook but got another HP notebook myself. The one i had to check was extremely slow. Switched the adaptor with mine and it ran suddenly fine like nothing’s wrong. Odd case but i wonder how many did think their laptop was broken while in fact it was completely functional…

    thumbs up this helped me BIG very BIG time!!!

  • Alick

    Did the new power supply fixed this annoying slowing down problem? I have tried almost everything under the sun. Please let me know. thanks!