Nexus 7 2013 Charging problem - Page 1
Forum section: electronics / repair

author: Prime
author_rank: Regular Contributor
timestamp: October 16, 2017, 01:55:39 am
content: So I've run into a problem with my Asus Nexus 7 where it no longer charges off the USB port. I don't think the tablet is hanging, I've tried most of the soft fixes I've found for that and had no success. Nothing happens when I charge it, t isn't even warm to the touch.The background to this is that I have a 15Ah SNUG powerbank with a qualcomm quick charger 3.0 plug, a skross world adaptor with a two port USB charging interface, and a Nexus 7 2013 tablet.I plugged the tablet and power bank into the charger and it started making strange noises, unplugged one and the noise went away. Charger still works but smells like death inside (can't open it yet) but seems to still charge. Tablet charged for a while and now longer charges.Bought a new wall adaptor while I was in Darwin. Plugged power bank into new charger, power bank charged up up to 100% (a bit too quickly for my liking) and then refused to charge anything else. Also smells like death inside.So I'm assuming the skross charger was the culprit.But my actual question is this, surely a modern smart phone or tablet isn't likely to be affected by a bum charger? As all the battery protection, and charge management sits within the device, surely it can handle a defective USB charger? From my experience with USB devices, the charge rate has more to do with the device than the charger as the device will pull the current it needs, rather than what the charger is capable of supplying, with the charger rating being the peak value?The other question is, does anyone know if the QI charging system is downstream (after) or upstream (before) the USB charging circuit? I'm hoping I can by a wireless charger as a fix but would like to know if it will actually workThanks

author: stmdude
author_rank: Frequent Contributor
timestamp: October 16, 2017, 07:01:51 am
content: Quote from: Prime on October 16, 2017, 01:55:39 amI've worked on this (different OEM though), and the answer is (as always), it depends.We had various forms of protection (reverse polarity, over-voltage (within reason), filtering, etc), but there were still ways to break our devices with misbehaving chargers. One in particular comes to mind, and it was a (likely defective) charger for a Kindle ebook reader that one of our internal testers noted "made the phone hot".Turns out the charger was outputting a 7V 60Hz square-wave... Yea, that would have broken our device, had it been left there for too long.Typically, our priorities were:1. Safety - Catching peoples houses on fire is _bad_ PR2. Performance - Charge as quickly as we can, but still honoring priority #23. Compatibility - Because playing the "which charger works with my phone" game gets old real quick.4. Reliability - Well, because it should break within the warranty period at least.Quote from: Prime on October 16, 2017, 01:55:39 amThe Qi receiver outputs 5V, so it feeds into the same USB charging chip. It might be a different input on it, so there's a slight chance it'll work.

author: Prime
author_rank: Regular Contributor
timestamp: December 10, 2017, 07:59:47 pm
content: Quote from: stmdude on October 16, 2017, 07:01:51 amThis is a fair and valid set of design requirements I guess.I opened it, hooked the battery up to a charger. The daughter board is bust because the tablet booted when I charged up the battery. Will have to find a daughter board on eBay and repair it when my funds allow.Sent from my HTC One M9 using Tapatalk