Sony VAIO laptop power supply LED goes out when plugged into laptop

Power supply is original and OK
When i plug charger into laptop, the charger LED goes out and laptop will not start
Battery is flat
Same result when i try with battery out of laptop as in
I am not pressing power button
There is no charge status LED on laptop
I tried removing power supply, taking battery out, turning laptop upside down, pressing power button for 45 seconds to release latent charge/static, putting power supply back in without battery.
Charger works on other laptop
Is this a short? How do I test to component level for the short?
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B HCommented:
does a different power supply work in the suspected problem laptop?  

have you confirmed the voltage output matches what the laptop expects?  (i have to ask, maybe a mixup with the power supplies?)

to test for a short, you're going to need a voltmeter, screwdriver, and to completely disassemble the laptop... it's a lot of work.

phil_swiftAuthor Commented:
I dont have another 19.5v power supply.
I have to buy a voltmeter to doubloe check output but I heard this can vary 2 or 3 volts when the PSU is not loaded.
I assumed if it powered another Sony laptop and it is the correct model for mine it is ok, maybe not...
I have some experience of taking laptops apart. I want ot fix it not buy another.
B HCommented:
so, this power supply that might belong with the problem laptop - does work on another laptop?  are they very similar in model numbers (the laptops)?

if you have two laptops, why only one power supply?  

i think the laptop is trying to pull too many amps, thus killing the power supply (temporarily).  

if your laptop wants 19.5v at 5.0 amps:
- you can get away with 18v-21v at 5.0 amps
- you can't get away with 19.5v at 4 amps

assuming the physical connectors even work (apparently they do tho)
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B HCommented:
oh - you might be able to find the short on the motherboard if one exists it's probably at the dc connector where the power supply plugs in.  that's not too hard of a fix, but usually requires desoldering and soldering on a new one.

if it's in a tiny resistor or worse a printed circuit, you'll need to be a master with a solder iron to get that fixed without destroying the board,  but it could be fun too

chances are it's a mismatched power supply.  toshiba standardizes all their recent laptops and power supplies, but sony (like HP) likes to do their own unique stuff with hardware and not follow any kind of rhyme, reason, standard, or uniformity

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it is possible you'll be able to locate a short - if it is near the dc-input jack.otherwise, it can be the charger section of the mobo is bad.
unless you're very handy with smd soldering, and have access to all bits and pieces needed - forget repairing it.

you can try these guys :
phil_swiftAuthor Commented:
Hi, it is the correct power supply model. I have tested it and it's output is 19.5V. I did not mention that I have replaced the power socket already and soldered a new one on. I now have a multimeter and will start using the resistance setting to check for a short circuit. I believe the power supply LED goes out to show that the internal trip has gone thus protecting the power supply. Thank you to everyone who has input, i will award points soon. Phil
phil_swiftAuthor Commented:
Laptop rescuer sounds good but Im in England and they are USA so I will try and find an English version of
B HCommented:
you might get lucky on ebay by finding a motherboard for that model cheaper than sending it in for repair :)
phil_swiftAuthor Commented:
The new power socket had slightly different tags to solder to and they had a thin sliver exposed on the side. I didnt check as it looked exactly the same. The + tag was shorting out on a this sheet metal clamp holding it in place. I insulated it and it all went fine after that. I am going to use an illuminated magnifying glass for board work from now on!
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