Laptop Repair Attempt - Acer Aspire A515-52G-75YQ - not turning on - Page 1
Forum section: electronics / repair

author: A5tro
author_rank: Newbie
timestamp: February 19, 2022, 02:08:50 am
content: Hi everyone!During the last months I got into electronics and managed to fix a couple of things.This week I wanted to attempt my first laptop repair.Well ... I got to a point where I thought it might be better to ask for help.I am very grateful for everyone who takes a look at this!Short Version:Nothing turned on but it drew 4W from the wall.Measuring voltage rails at inductors: only 19.5V from PSU present.Measuring resistance at inductors (shorted rails?): they look fine (I think?)Searching for hot components: found hot step-down controller on back side (TPS51225C) (dual step-down + 5V LDO +3V LDO (I_max_LDO = 150mA))Measuring for shorts on its pins: pin 3 (VREG3) is only 6 OhmsFaulty controller or periphery? --> desolder controller (bought a cheap hot air station)Pin3 still 6OhmI started checking components that are connected to 3V --> too manyinjected voltage instead: 2V (400mA) (I started lower but couldn't find anything getting warm)The only obviously warm/hot component is UB1 (KB9022Q) which is a big LQFP128 embedded controller. I guess that needs to be programmed for each board-model individually?Could it be something else? Have I done something wrong? If it is UB1, can I still fix it? I have never soldered a package this big and surrounded by so many tiny components. Is there a chance I could program a new controller? I am not sure what to do next. :/Extended Version:I documented what I did along the way by making some slides (measurements and images). I attached them as PDF.Here are the links to the schematics and datasheets that I found online:step-down controller TPS51225C:https://www.ti.com/lit/ds/symlink/tps51225c.pdf?ts=1645122313982&ref_url=https%253A%252F%252Fwww.google.com.br%252FMainboard:https://www.badcaps.net/forum/showpost.php?p=1064521&postcount=5Platform controller KB9022Q: (Did Not Find) but there is a pinout in the mainboard schematicsAgain huge thanks to everyone who takes the time to look at this!BestAdrian

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: February 19, 2022, 04:18:08 am
content: Check any suspect MLCCs(the tan colored surface mount devices).It is pretty common for them to fail, and they almost always fail in a short or fire.

author: A5tro
author_rank: Newbie
timestamp: February 20, 2022, 08:04:05 pm
content: Hi Alex, thank you for your answer!Without any further soldering I measured the resistance across all the caps that are close to UB1. The only ones that measured low where filters across shunts and of course those that are connected to 3V.I guess the only thing I can do in order to isolate the problem is to remove more components.But I found something else while measuring the resistance to ground for all the pins of UB1.On UB1 the pins 53(KSO14), 54(KSO15), 55(KSI0), 56(KSI1) belong to „nt. K/B Matrix“ and go directly to the keyboard connector (no additional components connected). And they all have a pretty low resistance to ground (between 4.1 and 173 Ohm). All the other pins that go to the keyboard connector show "OL" .... and I guess they all should.Also said pins have low resistance across each other.I looked inside the keyboard connector, in case there might have been something bridging the pins, but found nothing.I would interpret this as a short inside UB1 and the only way to make sure (that I can think of right now) would be to remove it from the board.Looks like a good idea to search for big chips in my trash box and practice removing them....And I should take a look at the keyboard.

author: rob77
author_rank: Super Contributor
timestamp: February 22, 2022, 11:30:41 am
content: +3VLP is not going to much places... check the schematic.. couple of pull-ups for signals, power button, lid switch, and the 9022 of course... try to desolder the ferrite bead towards the 9022 and measure resistance on the rail. if still low you know at least it's not the 9022

author: A5tro
author_rank: Newbie
timestamp: February 26, 2022, 03:49:10 am
content: OK, so I calmed down and measured again to make sure I didn't miss any hints to what might be wrong. (I desoldered LB1 for example.)Then I went on to desolder the 9022 .... and had a little upsi ... the chip slipped and knocked 9 SMDs off the board.I picked them all up, resoldered them and measured everything to make sure they were all on their original places.Sadly the keyboard connector now looks a little bit toasty because those components were pretty close to it. But other than that, I think I saved it.I hope the ferrite beads are fine, as I had to heat the area multiple times and one is maybe slightly darker than before?Once the 9022 was removed, the short was gone.And it turns out that just 40km away there is an electronics shop that sells these chips pre-programmed for my exact motherboard! Incredible luck!Now I don't need to buy the equipment for 90€. I payed 25€ for the chip instead.So next week I'll try to solder the replacement on there.Thanks everyone for the help so far!

author: A5tro
author_rank: Newbie
timestamp: March 04, 2022, 09:42:51 pm
content: Short update:I soldered the TPS51225C and the new KB9022Q back on.I inspected all the pins and checked for shorts where I thought it might be necessary.Then I installed the heat sink, screwed the mainboard into the chassis, connected the screen and power cable and turned the machine on by shorting the ON/OFF signal line to ground.The backlight turned on and off a couple of times (restarts?) and finally I had a picture, showing "No bootable Device".I thought "Great! It's fixed!". So, I spend an hour, trying to clean it and get all the flux residue out of the connectors.Then I connected the rest: touchpad, keyboard, daughterboard, battery.I connected power and thought "Great! it is charging!" as it was taking 28W from the wall.I pressed the power button ... and nothing happened.I shorted the ON/OFF-line to ground ... and nothing happend.I disconnected everything and tried again ... and nothing happend.Sooooo, looks like I broke it again?It is definitely not the same error as the first time. +3VLP is not shorted to ground. 3V and 5V are present. The battery seems to be charging (when connected).Powerdraw goes down and the power LED lights for a couple of seconds after pressing the power button. So "nothing happened" was not quite true.Well, when I have time I'll work through the power sequence in the schematic and report back.

author: A5tro
author_rank: Newbie
timestamp: March 05, 2022, 02:28:54 am
content: Okay, that was quick.I started measuring and once I hit the power button, it simply worked again!Super weird. I have no idea what changed.I got into the BIOS (which looks a little strange, as it is missing proper model information and even spells Aspire as "aspier") but couldn't get it to boot from USB sticks.Booting a Gparted-CD and a Win10 installation CD worked though.But unfortunately the trackpad does not work!Power and enable are present but probing the signal lines with my oscilloscope shows that there is nothing to see. Not even a clock signal.I of course tried to activate the touchpad with the function keys on the keyboard. This successfully toggles the enable signal but that's it.TP_CLK and TP_DATA go directly to the 9022 while I2C_1_SCL and I2C_1_SDA are connected to the CPU through two mosfets.I am not sure who is supposed to generate the clock signal here and also why the trackpad is connected to both the CPU and the 9022?Or could this be a simple driver issue?I'll have to buy an SSD first, before I can get into windows and try installing drivers.It seems strange to me though.Edit: Also the Bios is out of date. But I can only update that within Windows as it seems.Update: It works now!Apparently the windows DVD that I had flying around in my live-CD collection was too old. I made a new one and there the touchpad works. Great! So it was a driver issue.(Note: TP_CLK and TP_DATA were not used. The touchpad works over I2C and is only communicating while being touched.)

author: abdulbadii
author_rank: Frequent Contributor
timestamp: March 05, 2022, 03:52:20 am
content: always update BIOS by getting from PC's brand web site, here Acerbetter use/install light OS first to alleviate work e.g. Linux (MX Debian, Artix) then so ready Win 10