| Electronics > Repair |
| laptop power IC died, help iding it, yQDQA/yQDQ4 marking, acer ph315-55 |
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| DavidAlfa:
Ceramic caps LOVE to short out. I've fixed a ton of expensive laptops where the culprit was a shorted 3.3Vaux cap, happened specially in Lenovo and Acer devices. Inject 3.3V limited to 1A and see what heats up, if the short is very hard then it might need a lot more current, sometimes up to 5 Amps! 3.3V is basically connected to a thousand parts, you can't really diagnose a hard short even with the schematic and / or boardview, maybe with a microOhm meter, but not a common device. A typical DMM won't be able to show anything either, as the smallest step is usually 0.1Ohms. The easiest way is the current injection, if you have any small PSU at home. You could make your own with an ATX PSU, connecting the 3.3V output through 2.2R 5W power resistors. Buy two, first connect only one, so the current is limited to 1.5A. If nothing heats up, connect the second resistor in parallel for 3A. The resistors will get pretty hot, so keep them away from everything, will melt plastic parts and cause burns if not handled properly. |
| SeanB:
You can see the cooked ceramic capacitor next to the PL silkscreen on the board, 2 ceramic chip capacitors, and an inline ferrite, with the capacitor looking very smoked, and a bead of silver extruding from it. Remove and replace with a new one, probably something around 22uF 10V, not too critical as it is X7R, and likely varies wildly anyway. you can even scrape off more of that soldermask by the capacitor, avoiding the tented vias, and solder in a 22uF 16V tantalum there, and get the same performance, just with less fireworks, as there is room, and there is enough height for a tant there anyway,. |
| DavidAlfa:
But PL311 is the input (19V), not the output. |
| SeanB:
Then use a 25V part, again with replacing a multilayer ceramic any value from 4u7 to 22uF will work there. |
| Anthocyanina:
thank you, i'll see if i have a supply that can source enough current to try that. about the capacitor. it fell off when i was probing last week when i first encounter the problem. i cleaned the pads today, the only new development, regarding the hardware, is seeing there is still a short on that rail. there's another development, i plugged the os drive to my desktop, booted from it, and see the shutdown happened as scheduled according to the event viewer, so whatever killed that chip and anything else that is dead happened either on shutdown or after the computer was already off. I had scheduled a shutdown(falling asleep to a netflix show) so i was asleep when the computer died, but good to know it didn't happen when the computer was still on, that could be a clue, at least going from the power sequence timing in the pdf. thanks again! (still would appreciate a boardview if anyone would like to share) edit: thinking about it a bit more, it seems whatever happened at the exploded IC's location was not the cause, but a symptom. its output doesn't have current limiting protections in place, so i think it likely that the 1 ohm short on the rail pulled too much current and caused the explosion. this does not explain the shorted cap at its input tho, nor how it could have happened at or after shutdown, hmmm! |
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