I bought a Nexus 7 Google tablet for family use in 2013, the 32GB unit with the cellular option. The family likes it, no complaints, its a nice device. My wife uses it daily for various different tasks, primarily relaxation, mainly NetFlix and Kindle e-reading.
On an unrelated note: I’m pretty sure she’s made a permanent place in her life for a tablet experience. She uses the household tablets much more than she uses her notebook. I get the sense that she thinks that “Notebooks are for typing work” and “Tablets are for relaxation”. I think I agree.
Oh yeah, the Nexus story. Last week she pointed out that it was no longer charging. It had apparently been “acting up” for quite a while. I switched her to an older iPad and I relegated the Nexus to the shelf for later inspection.
I got around to looking at it today.
First thoughts; Looking at the USB connector, it feels like it has too much movement in it, when the charging cable is connected. The male charging end was moving by 4-5mm in total. That’s more swing than I remembered. I had a hunch that maybe we’re just dealing with an overly assertive user, or general wear and tear. Over time, had the internal solder joints for the 5v rail simply worn out?
I checked the external power supply and cable with another Android device. Its working fine, meaning the problem is within the tablet.
The tablet itself didn’t power on with the charger attached, regardless of how I positioned the usb cable. While this doesn’t necessarily disprove my loose connector theory, generally it points at something else. I continued with the debugging.
I popped the back cover off the tablet easy enough, using a spudger and started looking at the USB connector area itself. A close inspection of the connector showed obvious signs of wear on the delicate internal mating pins. If you look at the mechanicals you can see that inside the housing of the connector is a delicate 5 pin plate. At the rear of the housing, where it attaches to the PCB, are the typical 5 pin mounting/power points.
Internally, the connector looked worn but was firmly fixed in place. Attaching the USB charger and measuring power on the rear mounting pins resulted in a very reliable 5V. The problem wasn’t the USB connector and its apparent 4-5mm motion. The amount of motion in the connector is simply the result of a cruddy mechanical design. I don’t like it at all.
Moving on, I looked at the battery. I measured two 3.8v rails, nothing unusual here. I hooked up the oscillocope to the terminals to see what would happen if I looked at the 3.8v rail while attempting to power the device up. Interesting, I see a small amount of ripple (± 150mv) on the supply, for a few seconds, then nothing else. While attempting to power the unit up, something is drawing current, causing an apparent drop in power. And, best I can tell, the battery has power. The power switching can now be ruled out.
Summary? A dead processor, or other critical component.
No audio is heard when power is applied. No lights appear, no vibration, a completely dead unit. This likely rules out the screen, the battery, the controls and I’ve already ruled out the charger.
While I can’t be certain, given that it has power already in the battery, its probably not the charging circuitry either.
Other than maybe putting the device on the shelf, and repurposing the hardware in a future project, its a dead weight. It went into the garbage today.
Copyright © 2015 Steven Toth