DELL Inspiron 5150 - Power problem

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I have a problem with my Laptop Inspiron 5150. These are the symptoms:
Without a battery and with the power adapter plugged into the
laptop...pressing the power button causes nothing, only I can observe
the two outer most LED’s of three on the front edge of the laptop to
flash on for a split second every 7 second.
With battery power and power adapter plugged in, the laptop works using
battery and no charge the battery. It seems to be a DC/DC converter that
is on the motherboard, has somebody experienced this problem ? how to
solve it ?

Re: DELL Inspiron 5150 - Power problem

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This problem occurred on a machine (same model) belonging to a friend
of my wife, and I was called in to fix it. The initial problem was that
the DC in jack was broken off. I had assumed this was the ONLY problem.
When I had fixed this, I found the exact symptoms you describe.

I checked output V from the adapter, it was good and stable. I tried
powering the laptop off my lab PSU just in case - still no dice. I told
her to order a new motherboard and she bought it off eBay. Swapped
motherboard, same symptom. Must be a common problem. I traced through
part of the power circuit to check for open resistors and fuses and
shorted semis... nothing.

You'll notice that the +5V standby voltage is present but low. The 3.3V
rail keeps going up and down as the LEDs blink.

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