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HP Pavilion ze4300 power button/PSU problem - power wont hold ON

Hello,

Im trying to figure out a fix for this Laptop that was working fine, was installing a load of updates and the machine had been running fine (fan was on and getting warm) then phut !.. it all goes out since then if you press the momentary power button you get all the lights come on but only for a second or 2, then they all go out.

Battery is fine, as is the powerpack ive stripped the unit down to motherboard (less HDD and CD) to try and work on it, seems to me like whatever 'holds' the power on when you release the key has failed (theory sounds simple!) but does anyone know where to start, i dont have any schematics or knowledge of this laptop.

Measuring around the motherboard im seeing 5v on the switch pcb, 16.5v near the battery 3.3v near the switch connector.

Any ideas very welcome!
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Benboben
Asked:
Benboben
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1 Solution
 
rbudjCommented:
Do the fans spin when the laptop is turned on?
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edbedbCommented:
Check your RAM. Try reseating the modules. Replace it or try starting the computer using 1 memory module at a time in different slots.
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rbudjCommented:
You did not mention that you opened the laptop but I have seen this happen with a crimped ribbon.
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BenbobenAuthor Commented:
Thanks for the suggestions, ive just tried removing the dram modules (2) and also the wireless adapter and re-checked - same thing, power doesnt stay on.  You press the power button all the lights come on (no fan activity) then even if you hold the power button down, all the lights go out after 1-2 seconds.

Im thinking its unlikely to be trapped cables, as the laptop died while it was running but was getting hot, so im thinking a MOSPET or transistor that holds the power on could have failed, just no idea where to start looking !
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nobusCommented:
here my laptop troubleshooting guide :
-remove all external devices
- if no display - test with an external monitor
- test if it runs from battery alone, or from AC alone
- test also with a known good battery !
- remove battery and AC adaptor, hold power button for 20 sec, connect AC and reboot --> any display ? if NO -->
- disconnect all disk and cd drives, battery , and other cards and peripherals, leave only 1 ram stick
- boot -->any display ?
- if NO remove all ram and reboot --> if NO beeps, mobo or cpu bad ; if it beeps, replace ram stick
-if you can access the bios battery, remove the battery, AC, and bios battery for a minute to reset the bios
or test it, it should read 3 V
*** you can test the disk on another pc, if you like !
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BenbobenAuthor Commented:
Nobus, thanks for the ideas.

I tried the battery out no AC, but get the same result on battery only or AC only.

I dont think the power rails are holding up long enough for anything to get started, I cant see anywhere a bios battery, is it possible this machine doesnt use one? do some laptops use flash or E2PROM instead? or could it be hidden under the motherboard somewhere?.  If that was flat tho, wouldnt you still have something working ie screen etc? perhaps with some error messages?
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nobusCommented:
>>   If that was flat tho, wouldnt you still have something working ie screen etc  <<  not necessarily, it depends on the bios, and the board

is there one?  i'm not sure; page 2-62 talks about one to replace, but never show it
also- they say that it must beleft charging for 24 hrs?  all the cmos batteries i've seen were cell batteries -unchargeable

did you also reset the laptop from the switch (under the hole in the bottom) - if not try that also

servixce manual :  http://www.karlin.mff.cuni.cz/~motl/hp-keyboard/manual4700.pdf
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BenbobenAuthor Commented:
Nobus,. many thanks

I dont think it has a battery for cmos, it mentions E2PROM so perhaps it uses this,

I tried removing batt + AC, holding reset down but still no difference, still think its something on the motherboard.  

Could there be a temp sensor that switches the power off if it gets too hot thats gone o/c or similar?

The service manual link is very useful, ill take a read of it, i wonder if i can somehow get a schematic?
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nobusCommented:
i never found any schematics of any motherboard - if you can find some, please post them
did you try trhe reset button ?
since you have it open, AND it is useless as it is, i would also remove and reseat the CPU - and inspect the pins
also renew the heatpaste !
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BenbobenAuthor Commented:
Did some more checking, incase something like the AC adapter power socket faulty causing the battery to be flat, anyway the power in from the adapter is solid, and i can find 3.3v and 5v rails on the motherboard when on the adapter only.  I think the processor power isnt getting started, dont think im going to fix this without a psu section or motherboard schematic, is there any way to get them for this laptop ?
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nobusCommented:
see my post above ..
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BenbobenAuthor Commented:
Ill try removing the CPU and seeing if the rails come up with it out, do you think this is a good or bad idea?
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nobusCommented:
>>  seeing if the rails come up with it out,  <<  rails? cpu ?  never saw a cpu with rails plse explain
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BenbobenAuthor Commented:
Meant "power" rails, I missed a word out :)   As you say i doubt anyone releases schematic info so i probably wont be able to locate whatever has failed. Ill try the CPU idea next.
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BenbobenAuthor Commented:
Tried removing the AMD athlon processor, same response to pressing power button, re-placed it and no difference,, looks like its a throw in the bin job !
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nobusCommented:
it starts looking that way, yes
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BenbobenAuthor Commented:
Thanks for your help
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