Another dead tablet

[joeqsmith]

Another one of my tablets failed.  The power supply is located under a metal can near the center of the unit.  I was going to attempt to repair it until seeing the damage.   I like these tablets because of their small size and ability to run Labview.   There is just not enough room to carry around a 10"   

Looking at new tablets, they all seem to ship with Windows 10 and most are fairly large.   My experience with Windows 10 has left a bad taste in my mouth that no amount of dental floss and rinse can remove.   

I am thinking to see if I can get Windows 8 to run on a cheap tablet from NuVision or something. 

[TerraHertz]

Was that a heating cascade started by component failure, or liquid ingress causing corrosion then heating?

[NiHaoMike]

Looks like a leaking supercap, similar to what caused some Fluke multimeters to fail.

[joeqsmith]

Well, I can't say the this tablet has not seen a fair amount of abuse.   It gets taped to the one bike and I use it to log data.   So some temperature swings, sits in the hot sun and vibration.   I don't ride the bikes in the rain but it's possible it may have had some moisture inside from condensation.   There were no signs of anything else happening except this area of the PCB. 

The tablet had been working fine and I went to turn it on and it was dead.  I put it on the charger and the charge light would not come on.  I popped the cover, checked the fuses and they were all fine.  That's when I lifted the cover. 

Looking at it closer, there is a fair amount of copper splattered inside. 

I was able to remove a few of the parts from this board to repair another tablet that had failed. I have some time now to try some of the newer ones. 

 

[joeqsmith]

Before I started to strip the board for parts, I hit it with some cleaner.    Looks like both SW, BTST and PMID pins are gone along with a couple of pads.  The link is to the datasheet for the charger IC. 

http://www.ti.com/product/BQ24196

[TerraHertz]

Electrolysis is a bitch.
But the question is, where did that conductive paste come from in the first place? It looked like more than just water ingress plus corrosion products... maybe.

I couldn't see anything that looked like a supercap, and anyway why would a tablet with permanently connected battery need a supercap?

Did you ride your bike through a mist of cat pee or something?

[joeqsmith]

The cat uses a litter box and the dog goes outside.    With it being in the center of the tablet, under that cover, I would think I would see signs of moisture around other areas but it all seemed clean. 

When it starts to cool down at night, we get a lot of condensation.  I use Cat Crap to help curb it on my helmet.   Maybe it was a buildup overtime from condensation but this is the only area that was effected.   I may need to conformal coat them. 

[BillB]

Maybe if you put it behind the fairing, rather than using it as the fairing it might last longer. 

I kid!

[Monkeh]

There certainly appears to be a supercap right there, coincidentally at the top of the affected area..

[joeqsmith]

I pulled the cap and it does appear that it leaked.  This tablet has been held to the bike by velcro, it's seen ground speeds most tablets would dream of.  It's been dropped, heat cycled in a trailer and with all of that, worked flawless.   Now a few cent cap leaks and destroys it.  A proper ending for it would have been having it fly off the bike and skip down the pavement.   

[joeqsmith]

Inspected the working tablet and it looked fine, until I removed the cap.  Looks like it wouldn't have survived much longer.   So thanks for asking.  I wouldn't have checked otherwise.   

I've been looking at the manuals for some of these inexpensive sub $100 tablets.   They don't have the GPS like this one does but have same memory.  My guess is the processor is going to be a wash for what I use them for.   The one thing that may be a plus is it looks like they solved the power problem.  To use the Lenovo, I had made a custom USB harness with a button to short the two data pins while you turn on the tablet.  It thinks it is hooked to a charger.  Then you release the button and it stays charging but frees up the USB port.   The manuals for the newer ones look like you just plug it in.   

Some have HDMI, so I could put a big screen TV on the bike. 

[stj]

oh shit, i just got a lenovo tablet!!! 
what model is that???

[edit]
o.k. board is from a MIIX2 8" model.

[joeqsmith]

Yes, both of these were.   I looked at getting another Lenovo but they didn't seem to offer anything like these.   Let me know how yours holds up.   

[stj]

one thing i noticed, there are a LOT of those MIIX2 pcb's on ebay - all "untested" (we know what that means)

[joeqsmith]

Looks like power is a problem. 

https://www.ebay.com/itm/Lot-of-6-LENOVO-MIIX2-8-ZIJH0-WIFI-TABLET-MOTHERBOARD-90005270-LA-A591P/162583713884?epid=2262495518&hash=item25dabe985c:g:dBgAAOSwQjNW-Z4v:sc:USPSFirstClass!49085!US!-1

[amyk]

The electrolyte in supercaps apparently contains sulphuric acid. Now you know why they're so devestating when they leak...

[joeqsmith]

I used some of the early supercaps and still have a few of them and they have never showed signs of leaking.  Wiki has some good overviews on them. 

The super cheap Windows 10 tablet arrived.  Very little bloat/ad ware installed beyond Windows 10 itself.  The Windows 10 tablet mode is alright but it does not appear as smooth as 8.  Zooming is slow.  I'm not sure why but when I launch an application, it does not come to the foreground.  Perhaps there is a setting for that. 

I had hoped that they would have sorted out the charging problem but it works like the old Lenovo and can't charge while using the USB port.

The really odd on is the resolution.   The lenovo was 1280 x 800 compared with  1920 x 1200.  So I would expect the software I wrote for the older screen size would be very small but they are not.  Strange stuff.   

For just browsing the web, email and stuff the majority of the people would actually use, it seems fine.


https://shop.nuvision.com/products/copy-of-tm101w635l-10-1-2-in-1-windows-pc-tablet