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Author Topic: Laptop not starting, no power problem  (Read 1441 times)

Laptop not starting, no power problem
on: March 09, 2010, 17:51:28 PM
Hi, dont know whats wrong with this, its a toshiba u300 laptop, with the battery in it doesnt start, no lights no nothing, with the battery out if I put the power lead in and out a few times it will boot, I can then put the battery in and remove the power lead and it works fine, the battery charges fine, with the power lead in.
If I remove the battery and the power lead, hold the on button for about 20 seconds, put the battery in it will boot, then if I turn it off it wont boot again unless I remove the battery again and hold the on button.
I dont know if anyone has any idea what this could be, it seems the power has to be drained for it to boot, Ive had it to bits but cant see anything, but then Im a mechanic and I dont think a hammer will fix this.
 Thanks for looking.
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Re:Laptop not starting, no power problem
Reply #1 on: March 09, 2010, 18:43:38 PM
Sounds like a short on the power - or the power adapter could be on its way out.

Seen plenty of PCs that looks like a dead PSU, but unplug the PC from the mainboard & the HDD, CDROM,etc. - plug back in
& everything works again.. usually caused by a short or a PSU thats on its way out.
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Re:Laptop not starting, no power problem
Reply #2 on: March 09, 2010, 19:53:05 PM
Thanks for the reply, it cant be the power adapter because Ive not used it all day, but what you said just made me disconnect the power adapter plug from the mainboard, this never helped but Ive now found something that does.
I found the cmos battery was dead so fitted another, this never helped but it made me check the board with a voltmeter, only the cmos battery in, I found a capacitor(the biggest one) and some chips around it had 0.8v, these were near the main battery and power adapter sockets, when you said about the power adapter and I disconnected it, I put the main battery in and it booted, turned it off then it wouldnt start again, I checked the voltage that was 0.8v before and it was 3.5v and decreasing as I left the voltmeter on, when it got below 2.0v the laptop boots, so it seems the voltmeter is drawing enough power for the laptop to boot.
I dont know if anyone can follow this(Im finding it hard) but Im going to try it a few times and come back with the result.
 Thanks.
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Re:Laptop not starting, no power problem
Reply #3 on: March 09, 2010, 20:49:47 PM
ok just been trying again, at first it didnt work, as putting the voltmeter on didnt make it boot, I removed the battery and held the power button for 30 seconds, then it booted, then I checked the volts and it was 12v going up to 13v then suddenly dropping to 3v then 2v and the laptop booted, I did this 3 times and it worked every time, I then just left it a while and it wouldnt boot, I check the volts and it was 13v then suddenly went down to 2v then it booted again.
Ive now done it several times and the voltmeter is making it boot, so some questions,
Does a voltmeter draw current
Why does removing the battery and holding the power button down then make it boot(what is it doing)
what would be holding the volts that stop it booting(and why)

Ive just left the laptop after turning it off to write this, I just tried to start and nothing, checked the volts and it was 11.5v slowly going up to 12.4v then dropping quick to 3v then a bit slower to 2v, then I tried to start and it booted.
So Ive found the problem I just dont know what it is lol,
Any of you electronic guys want to have a say?

I know this is long and hard to follow, but its the best I can explain.
 Thanks.
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  • Offline Serious

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Re:Laptop not starting, no power problem
Reply #4 on: March 09, 2010, 23:05:03 PM
Usually a dodgy charger cant supply enough power to both charge the battery and boot the computer, so nothing much happens unless you remove the battery. This might also indicate a problem with the battery. It needs to charge up the capacitors to a suitable level before it boots, which normally takes a fraction of a second.

The capacitors are for power smoothing and can hold charge for quite some time, ask someone thats touched one in a TV or even camera flash. Unless we know exactly what you are checking with the voltmeter it isnt much help.

Saying it cant be the power adapter because I havent used it all day is being excessively hopeful. It doesnt matter how long you havent used it for a failing PSU will cause issues.

The voltage across the input from the PSU should match the rating, worth checking this. Should be about 19v for a laptop PSU. Actual voltage will be printed on the label but Im damn sure it isnt 12v.
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  • Offline bear

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Laptop not starting, no power problem
Reply #5 on: March 09, 2010, 23:07:32 PM
My travelmate 5320 did not want to boot, my friend told me to remove CD/DVD player and refit and the f**ker booted !!!
I also refitted the memory sticks for good measure but they were fitted good and I believe the rmoval/reftting of the player did the trick !!! Worth a try just one screw to remove player. I figure a bad power connection can make current
flow wrongly ?
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Laptop not starting, no power problem
Reply #6 on: March 09, 2010, 23:29:24 PM
Quote from: bear
My travelmate 5320 did not want to boot, my friend told me to remove CD/DVD player and refit and the f**ker booted !!!
I also refitted the memory sticks for good measure but they were fitted good and I believe the rmoval/reftting of the player did the trick !!! Worth a try just one screw to remove player. I figure a bad power connection can make current
flow wrongly ?


Ive got it in bits, just the mobo, chip, a stick of ram and the power switch, think that rules out the optical drive.
Ive looked all over for a bad/dry connection, cant see anything, strange thing is theres an earth cable that goes from the main power connector to the plastic body, why would they do that?
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  • Offline Beaker

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Re:Laptop not starting, no power problem
Reply #7 on: March 10, 2010, 00:39:33 AM
seriously, try a different power supply.   If the PSU brick is bumping up the power feed when the computer starts to demand more then youll have problems.  My old HP used to only feed about 5v when the laptop was off, but when you turned it on the circuitry detected that, and started throwing 19.5V down it  
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  • Offline bear

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Laptop not starting, no power problem
Reply #8 on: March 10, 2010, 01:05:06 AM
If I understand correctly u can get it to boot with a charged battery with the powersupply disconnected , doing the voltmeter thingy if so the PSU should be ok I think
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Re:Laptop not starting, no power problem
Reply #9 on: March 10, 2010, 07:10:52 AM
For the price of a PSU on the bay of E, Id go down that route.

Theres a place near me that do laptop repairs if it gets that far.
http://www.realelectronics.co.uk/
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Laptop not starting, no power problem
Reply #10 on: March 10, 2010, 10:23:26 AM
Quote from: bear
If I understand correctly u can get it to boot with a charged battery with the powersupply disconnected , doing the voltmeter thingy if so the PSU should be ok I think

Correct

Guys Ive got about 5 psus, the psu is not the fault,  its a laptop if a fully charged battery doesnt make it boot how can a non connected psu be at fault.
I need to know why discharging the board allows it to boot.
My guess(and its only a guess)is, when the laptop is turned off the capacitors should discharge, but they(or it) doesnt.
 Thanks.
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Re:Laptop not starting, no power problem
Reply #11 on: March 10, 2010, 19:52:29 PM
Ive been reading up on batteries, and they do a lot more than youd think, although it can run the laptop for over a hour, I wonder if it should discharge the capacitors when the laptop is turned off, and its not doing it.
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Re:Laptop not starting, no power problem
Reply #12 on: March 18, 2010, 20:40:28 PM
It was the battery :nana:
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Re:Laptop not starting, no power problem
Reply #13 on: March 18, 2010, 21:10:57 PM
Quote from: filbert
It was the battery :nana:


kind of weird it wouldnt work without a battery
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