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HP NC6400 shorting? randomly with reproducible result


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#1
Alysher

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first things first, a bit of background. i have 14+ years of computer repair and hardware troubleshooting experience. in that time if have built hundreds desktops, but until recently had only done like 4 or 5 laptops.

i bought a HP NC6400 off ebay that was for parts or repair and repaired it. i have replaced the case bottom, motherboard, ram, hard drive, heat-sink, keyboard, LCD, inverter and screen bezel. there are also 5 screws missing out of the bottom of the case(waiting on replacements)but after putting this laptop together every thing works fine except this one random issue.

I'm calling this a short cause of whats happening. the screen goes out(light and and picture shuts off)the power stays on, and the mute button on the media board lights up. i can reproduce this if i pick up the laptop, or flex the case bottom (pick up one corner) while its sitting on a desk or table. i have also had BSOD show up a couple of times. i should probably mention that the first time turning the laptop on after rebuilding it started to power up and then started a constant reboot cycle. i pulled the system apart again and checked to see if the mobo was touching something on the case bottom, which was and got fixed. since then i have had the system apart once more to check for things touching which was what i had thought was the issue and i even covered the metal places that i thought might touch the mobo in the wrong places(spots that screws didn't go to)with anti-static tape. upon reassembly i changed the position of some of the case screws to help keep the laptop from flexing as much, and it seems to help, but i still have the same issue.

now could this issue be the missing screws in the case, or am i missing something. since this it the weirdest thing i have EVER seen or experienced i am at a loss as to what to do. any one with any ideas would be more then appreciated
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#2
phillpower2

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:welcome: Alysher

i changed the position of some of the case screws to help keep the laptop from flexing as much, and it seems to help, but i still have the same issue.

Have you used the correct screws in each location, see section A Screw Listing @ http://www.levnapc.c...isni-manual.pdf an incorrectly placed screw could cause this, another possible cause could be the MB to screen ribbon or connection socket/s, check the condition of both, the backlight is another possibility, two things you can check before you do a full dismantle are 1: To check if it is the backlight shine a flashlight into the screen and look closely to see if there is a display in the background (desktop icons etc) 2: To check a display cable/connection problem try hooking the notebook up to an external screen via the VGA port, you may need to toggle between screens using the Fn and one of the F1 to F12 keys or a single function key on the notebook.
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#3
Alysher

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Thanks for the reply phill,

i double checked my screws and the only ones Ive moved are the ones that are interchangeable(the Torx8 T8M2.5×11.0 screws for the base its self, theres a total of 16 of these screws, 3 for keyboard, 2 for switch plate, two for monitor mounting and 9 for the case bottom. i left the monitor ones, the switch plate has none, took 3 from base and used for keyboard). as for the screen, it completely shuts down, and all the connectors are solid, even the external monitor dont work when this happens. i also noticed that if i put a card in the smart card reader the stability goes up more, but it still happens, even taping too hard on the keyboard or pressing too much with my wrist while typing causes the issue to happen.

any other suggestions?

Edited by Alysher, 04 February 2012 - 02:30 PM.

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#4
phillpower2

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You are welcome :thumbsup:
I agree this is an odd one, as the notebook is only loosing the display but not powering off altogether the video chip may be the culprit.
When you connected to the external screen did you get a display at any time at all?
For reference it is Fn + F4 to toggle between the notebook and an external screen.
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#5
Alysher

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no display under external at all, and its not only the video that goes, power may stay on, but i cannot use the laptop at all, it locks up as well. i know i had stated that the mute button lit up when this happens, well i cant shut it off after. i havent checked audio, but im almost sure that i will end up with either audio stopping or a constant sound from the speekers when this happens. now why would this happen when the case is flexed and not be completely gone if it were video. as for reference, yes its fn + f4
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#6
Alysher

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OK, I'm going to add to my symptoms list.....

i checked again that the mute button wouldn't go off and was mistaken, but i cannot turn off wifi...

after forcing the short, if i fail to flex the case back the other way i end up BSoD every time i reboot it. i even had one say something about IRQ_NOT_LESS_THEN_OR_EQUAL_TO. now i have this issue one other time and it turned out to be bad memory. i am going to attempt to remove both sticks of ram(one at a time) and see how the system reacts...

ill post back with results in a while
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#7
phillpower2

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How many sticks of Ram are fitted?
If more than one try a single stick at a time, try each stick in each slot until all combinations have been tried.
What happens if you remove all Ram and power up?
There is a possibility that there is an issue with the circuitry on the MB as in when it gets warm it expands breaking the circuit, you may be able to see this if you inspect it with a magnifying glass.
Did the ebay seller state what the problem was with the item?
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#8
Alysher

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ok its 2 sticks of ram, and have tried all combanations. the mobo is actually a manufacturer referbished one bought off ebay. issue still showed up with all combanations of ram, so since i had the keyboard off i decided to check and see if i can narrow down where its shorting since i was having better luck lifting the side with the mulitbay rather then the side with the audio and hd on it. while i was testing i noticed something. now this model has 2 PCIE slots built into it, one for WLAN and one for WWAN, and since i dont have a WWAN card to put in it let alone a sim card i just let the contacts for the antenneas just sit in the slot.....one of the antenne contacts was touching the mobo as i flexed the case.....so i decided to cover the ends with some anti-static tape to keep them from touching the mobo...

IF this is my issue i am a doofus! talk about boneheadded stupid ideas...

going to do some testing on the machine now....we shall see what happens.

i didnt check with no ram in system....will do so soon

Edited by Alysher, 04 February 2012 - 06:25 PM.

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#9
phillpower2

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Good luck.
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#10
Alysher

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well no luck. i have narrowed the short down to the mobo its self. not the case or any of the peripals attached to the system(modem/pcmcia/bluetooth/wlan) now i know this isnt a good way to check things but this is what i did....i removed the mounting screws for the movo and tried to reproduce the short. i then picked up the mobo by the lan connector and got the short(mobo flexes after the modem mounts) i also picked the mobo up by the multibay connector and didnt get a short uless i dropped the mobo from about a 1/4 of an inch away from the case where the lan connector sits in the mobo.

now i know this isnt a very good idea, but all saftey precautions were taken. i looked closely at the mobo and i *THINK* that there is some excess solder around a compoent. would this cause the issues?

i know that the board is manaufacturer refurbished, but i REALLY dont want to send it back to hp for repairs. nor spend any futher money getting a new one.

thoughts anyone?
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#11
phillpower2

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i *THINK* that there is some excess solder around a compoent. would this cause the issues?

If it contacts with another component or circuitry yes, what is the component involved, the video chip perhaps!

i know that the board is manaufacturer refurbished, but i REALLY dont want to send it back to hp for repairs. nor spend any futher money getting a new one.

Notebook repairs are both time consuming and expensive and where the MB is concerned it is more often than not less expensive to replace the MB or complete notebook, hence the reason why ebay is inundated with notebook MBs.
Is this happening with just the battery fitted, battery and AC adapter or the AC adapter only connected.
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#12
Alysher

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not the video chip, there is a component that is on the other side of the Pci-e ports that looks as if the solder touches the other leads on it...and since i have a HORRID camera i cant really take a picture of it properly

and this issue happens under battery, ac and while both are in...

its OK, since the computer is my GF's shes decided to buy a new mobo for it...i normally wouldn't spend her money but the options for this mobo are slim at this point...thatnks for all the help.
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#13
phillpower2

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Thanks for the update and I am sorry we were not able to provide a solution, this would appear to be a time when a Techs diagnostic equipment is required.
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