Electronics > Repair
laptop power IC died, help iding it, yQDQA/yQDQ4 marking, acer ph315-55
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Anthocyanina:

--- Quote from: SeanB on December 11, 2023, 02:29:36 pm ---Then use a 25V part, again with replacing a multilayer ceramic any value from 4u7 to 22uF will work there.

--- End quote ---

yes, thank you, i know that will need to be replaced, but since there are still other dead parts in the board, i'll need to find them before replacing other parts
Anthocyanina:
so a few months i won a proper bench power supply and have been using it for regular home lab stuff as well as to try to find the short in this board, i've current-limited it to about 500mA and have been trying to find what gets hot, and nothing, so i set the limit to 1A, and at 1A i get about 300mV at the soldered terminals on the board, but with the 3.3V bus having so many components connected to it, the short might be very far from it, and i still can't find what gets hot, maybe the ~1W that's being put through the circuit it spread too thin and nothing gets hot with that? i've been trying the alcohol method, but everywhere it evaporates equally fast, so i haven't detected the short that way, so, what would you recommend? should i try with higher currents? any tips for finding shorts? i've seen people using the flux mist method, but i don't have access to that as i'm completely broke.

finding shorts in other stuff i've repaired has never been this difficult.

thank you
perieanuo:
usually my current limit was at least 8A to find what component is heating with back of my hand. thermal camera if you can get one will point also.
of course, at that current, the shorted capacitor just burns out, but i was on time constraints. most of laptops worked without even replacing the shorted cap, eliminating him was enough.
of course, try to raise current from 3A up if you wanna play.
br
DavidAlfa:
Keep increasing the current 1A at a time, waiting at least 30 seconds before increasing again and touching here and there for something getting hot.
Don't go right away to 5A or whatever, you will cause more damage to the the board if something burns out.
Anthocyanina:
ok! so today i decided to pick this thing up again for more testing, and i had given up on this laptop so i just turned the current to the max, at 3v and that surprisingly was using 10w, so i start poking around with my finger and found a seemingly empty spot on the board getting uncomfortably hot after a few seconds. i turned the board around, and i don't see anything, just some tape+shielding material that i had completely ignored last time, so this time i just peeled it off a little bit not expecting to see anything there, but this is what i found. this IC by the USB ports(in the attached image (it looked physically ok)). i removed it, tested again, this time the draw was about 3w, but it was getting hot in the same area, so i completely removed the tape and found another identical IC also getting very hot. I removed that one, and the short on the 3v rail was gone.

while removing the originally exploded IC, i accidentally removed some passives around it, easy enough to repopulate. But! now that i found the short on the 3v rail, i wanted to try powering up the laptop using the soldered wires that i used to find the short to get 3v up.

I tried this, and nothing at all happened. no charging lights, no signs of life at all. i only supplied +3VALWP, but the exploded IC also seemed to supply +3VLP. Looking at the power sequence, +3VLP comes on when the power button is pressed, or 2.23ms after AC_IN, not clear if it's the delay that brings it on, or if it's the power button press.

What would you recommend? should i also supply +3VLP with another psu?

as i'm still broke, i think i would only buy the exploded IC if it was confirmed that the problem is gone, but maybe that IC itself is necessary to dtermine if the problem is gone.

It's been about a year now since this died, and i've been taking a look at it every now and then, to see if i come up with something, and today has been the most productive day in finding the problem with this laptop!
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