Hi found my hub dead. Took it apart and checked voltage behind power socket. Voltage was zero after checking psu was delivering 5v. Found that smd fuse was hot so removed. The unit was still dead. I also noticed that the component next to it was also hot. This component is to supress spikes. I removed that also and the unit is back up and running. A perfectionist would replace these components but it would be nearly impossible to source them. Not the best fix but I now have my hub online again. Anyone who needs the exact details can contact me.
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This is when it would be nice to have a backup/restore tool. (listening to crickets, also listening to the sound of me beating a dead horse)
I would make sure to have it alt least plugged into a surge protector. Nice fix but it would make me nervous.
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If it is a capacitor you removed, I suggest you replace it. The filtration it provides extends the life of the remaining components. While it may work without it, there is a reason for its existance. Was it next to any heat emitting elements?
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No it wasnt a capacitor. It was surge protection which had gone short and a
blown smd fuse. Yes I will replace the components when I find suitable
replacements. I am guessing when my son set it all up again he accidentally
plugged in the virgin router psu being 12v rather than 5v. Shouldn’t be a
problem unless volts go high on psu, then it will be hub heaven. Bottom
line is it was dead now its working. And its someting to consider if you
have a dead hub. Not the cheapest things to replace. Btw I used to work for
an Icom two way radio retailer fixing duff taxi radios etc.
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Nobody fixes stuff anymore. Replace… sad 
Actually Andy you was right the component marked 120-6l f1 is a cap. The
other is as suspected a “voltage crowbar” to provide transient protection.
Shouldn’t cause probs without them in the short term.
If it’s an SMD capacitor, then it’s most likely there to filter out PSU noise on frequencies that would interfere with the MCU (it appears the hub does not have a full blown CPU?) or the radio components. Should work on the short term, but you’re better off replacing it 
https://www.digikey.com/product-detail/en/vishay-sprague/293D127X96R3D2TE3/718-1745-1-ND/2259966
https://www.digikey.com/product-detail/en/micro-commercial-co/SMA6F5.0A-TP/SMA6F5.0A-TPMSCT-ND/2770551
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Thanks for link you’re a star!!!
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Michael, can you tell me exactly which components you replaced / removed?
I accidentally plugged a 12VDC supply into my hub and smoked the component labeled “MCC SUA” immediately to the left of component “120-6L F1” in your picture.
I’m guessing it’s a multilayer ceramic cap but I have no idea what value to buy as a replacement.
Right now I have my hub running by hard-wiring the 5VDC supply to the battery terminals.
I’m having a nightmare thinking about moving everything to a new hub.
Hi mate
The component you “smoked” was a transient protection device. It tends to
go short circuit when it dies. I have been a lazy git and not replaced
mine. Btw I took out the smoothing cap next to it as well as it was short
circuit as well.
I guess my son accidentally stuck 12v into mine when he mixed up the router
psu with it. I wouldn’t worry too much about it as mine is still running
without either component. The switched mode psu supplied with the hub is
generally very stable.
Regards
Mick
Just re read you email. Desolder the mcc sua test and if still dead take
out the cap too, .
You will know if they are both duff as if you plug the psu back in they
will get hot very quickly. If they have blown and gone open circuit I would
guess your hub would not be working at all.
Thanks Michael. I noticed the two parts listed in the subsequent posts and was able to determine that’s exactly what I need, so they are on order. The transient protection diode actually split open, so I’m assuming it’s an open circuit and why the hub doesn’t work with the PSU through the standard input. I’ve got it temporarily working via PSU through the battery posts.
Hi
No probs. But if the diode blew open circuit then your 12v has got further
down the line. Hopefully the cap went short and put the 12v to deck . As
mentioned you can remove both parts and the hub should work. Mine is still
running without both as Im a lazy git. I have the new mcc sua but not
fitted it yet. The cap is really neither here or there just serves to clean
up any ripple. Personally I’d take the cap out and check continuity. Just
remember both these components go from the 5v line to earth. They are not
critical for proper operation. They are there in case of any issues with
the psu.
Let me know how you get on. Btw I repair amateur radios for fun!! Used to
do it for a living.
Regards
Mick
Replaced the diode (SUA) and everything is working again through the PSU input!
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Hi mate
Great news!! Its handy when people take the time to post fixes. Its not
just a case of saving money, it saves all the hassle of setting it back up.
Merry Christmas.
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Hi all,
Im new to the community and to smartthings. I come from the home assitant and openhab scene. Funnily my first experience with hub v2 has been horrendous. It worked for 2-3 hours after I realized that it was running on batteries with no warning. Checked the psu output with my multimerter and gave 5v disconnected, and weird voltages when plugged in. I opened the case, hooked up the scope to the 5v terminals and realized that the psu was sending an oscilating voltage between -3v and +3v at 50Hz !! wtf!. Finally got a bench psu and confirmed that the hub is ok.
I wonder if there’s other people having a faulty psu, this has never happened to me in my life, even with cheap chinese stuff. Faulty psu from the factory? Anyways, I’m writing this to get this incident registered in the forum, in case someone hits the same wall. Any usb phone charger of 2A or more can do the job.
Thank you for posting solutions to other issues like broken surge protector, or shorted caps in the input, before testing with a proper psu, I did remove and test those components out of the board and they worked as expected. Then the bench psu confirmed it, the psu was faulty.
Cheers
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Hi, i too accidentally plug in a 12v psu and now my unit is dead, can you show me how i can i fix this, thank you
Hi mate
Will dig out the piccy and hopefully get ot to you tomorrow. Its generally the transient protector and a capacitor. Plug it into the normal psu and check for hot components near to the input. Generally they should be too hot to keep your fingers on.
Regards
Mick
Thank you for the immediate reply, i have done what you said but i dont feel any warm or hot parts on the board, i read sockmonkey’s post bypass the socket by jumping the battrry terminals. It actually worked, good that version 2 has battery back up. It will do for now.