[SYDNEY] Request for repair/help - Page 1
Forum section: electronics / repair

author: jars121
author_rank: Regular Contributor
timestamp: March 28, 2020, 07:29:00 am
content: Evening everyone,I'm trying to resurrect my dead laptop, which has sat in my desk drawer in parts following some water damage.The good points:I've gone over the board in detail, and am fairly certain the damage was isolated to a single PMIC.There was only minor surface corrosion in the neighbouring area, which I've cleaned with isopropyl.With the help of some online commentary I was able to identify the PMIC manufacturer and part number.I sourced a compatible replacement PMIC (the OEM of the chip was obscure so I opted for a TI equivalent part).Despite there being no schematics available for this model, much of the power circuitry is carried over from adjacent model lines, so I've been able to verify the circuit by comparing it with schematics available online.If I'm unable to resurrect this particular motherboard, I'll be able to replace it with a refurbished one. This certainly isn't my preference, but fixing this board isn't be-all and end-all.The not so good:Some of the pads of the PMIC were damaged and/or badly corroded, so this isn't a simply resoldering job.I was able to desolder the dead chip without issue, but due to the missing and/or badly corroded pads, I wasn't able to solder the new part on. I don't have a circuit repair kit, so I made do with a single strand of wire which was about the right size for the 0.2mm SMD pad.In solder on the above jumper wire, the two badly corroded pads directly underneath more or less dissolved.So, as you can see, 3 sides of the QFN PMIC are fine. I imagine with the right tools and plenty of experience, replacing the missing pads and cleaning up the left hand side of the PMIC wouldn't be an insurmountable task. I gave it my best shot, but as I don't have a usable microscope (the photo was taken with a USB microscope that has a working distance of about 1mm, so you can only use it for inspection as opposed to actual rework), trying to solder a <0.2mm wire with the naked eye wasn't likely to work out (at least with my skill level).I'm based in Sydney, and would prefer someone local for the time being.Thanks!

author: JKKDev
author_rank: Regular Contributor
timestamp: March 29, 2020, 12:04:21 pm
content: I know it's not what you were looking for but hear me out. If (and only if) all the traces that lead to the chip can be jumped successfully you could try making a small PCB that would host the part and larger pads to solder wires to and glue it down. Then you just jumper all the contacts to some reasonable place and you are done

author: aqibi2000
author_rank: Regular Contributor
timestamp: March 29, 2020, 02:06:18 pm
content: Buy some UV curing mask and you just need some patience with some strands of wire.QFN pads are easily rebuilt

author: jars121
author_rank: Regular Contributor
timestamp: March 29, 2020, 07:17:23 pm
content: Quote from: JKKDev on March 29, 2020, 12:04:21 pmThanks for the inputI had actually considered doing just that, and may end up doing that in the longer term. I've actually come across a very reasonably price replacement motherboard which I've purchased, so the need to repair this one isn't as urgent as it was. I'd still like to get it back up and running though!Quote from: aqibi2000 on March 29, 2020, 02:06:18 pmThanks for the tip, I'll look into the curing masks