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laptop shorting out power supply when connected

Hi, when using my laptop in the car I had lost the end pin connector for the universal in-car power supply, and rather than buy a new power supply had instead cut the molded connector off of an old mains adaptor for the same laptop and bared back the wiring to fit into the pin connectors on the end of the cable of the in-car charger. But not thinking had forgotton to check which pin was pos. and which was neg. and must have had the polarity round the wrong way resulting in a spark at the connector as I was inserting the wires and the laptop switched off immediately. Also tripped the blade fuse for the power supply.
After replacing the blade fuse the charger works fine (with the correct adaptor!!!) on any other devices and wasn't damaged.
When home I plugged the laptop into the mains charger and the green light on the power brick went out as soon as it was plugged into the jack pin on the computer and would only come back on after being disconnected from the mains to reset it . Using the power supply on an identical laptop we have found it works fine but will trip as soon as it is plugged into the now faulty laptop.
When the laptop is switched on with the external power source removed and running on it's own battery it works fine, but when the external power is connected the computer switches off and the mains power trips.
I have removed the motherboard and had a visual inspection of the components and board and don't see any signs of damage or smell any evidence of a burned out part or pin.
I was hoping someone could help me in determining what I have done & whether or not the computer may still be repairable. I have not checked whether the jack pin is shorted out yet ( I will do this when I go home tonight)
but other than that I am at a loss as to what else would cause this fault.
The laptop is an Acer Aspire 5536 about three years old.

Hopefully someone out there has some ideas.

Downingtown, PA
·Verizon FiOS
It may, probably does, have a means of protecting someone from CONNECTING THE WRONG POLARITY.

Could be an open fuse, diode. Shorted diode. Some ohm readings of the input would be helpful. But certainly trace the circuit from the adapter connector and measure the components.


Thank you sparkchaser for your quick response, I'm going to test it with the multimeter when I finish work in about an hour or so and hopefully be able to track down the problem.
I had also thought that it may be a fuse on the board but had discounted that theory as I don't think that it would cause a short on the power supply as it has but infact just sit without power as the fuse would cause an open circiut. But I think maybe as you suggested possibly a diode has been damaged.

Technically feasible
West Hartford, CT
reply to elroy
I vote for a shorted polarity diode somewhere near the power jack.

·NorthWest Tel
+1 vote for diode.

Get your multimeter and start testing diodes around the power jack and power circuits area.

Any diode that reads close to 0 in both directions is what you're looking for. If you find one, de-solder it, test it out of circuit to confirm. Once diode removed, laptop should power up (with proper polarity of course!!!). If you want to retain reverse polarity protection in the future, replace new diode. Rating of diode isn't super critical. It's actually considered sacrificial.