Author Topic: DLA Active Hub Failure  (Read 2245 times)

Offline mkozik1

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DLA Active Hub Failure
« on: January 07, 2017, 04:28:20 PM »
Good evening,


Wondering if I can pick your brain to understand why my Active Hub is failing.  Last year I connected the micro SC's to my active hub and everything was running just fine.  One night I went outside and it was dark.  I checked all components and found that my active hub was not showing the green power light.  I did some digging and found that when using the optional power connections, when I turn on the power supply (nothing connected to the board) the green light comes on strong and then fades away after a little bit.  So ..... Thinking this might be the optional components, I tried a PC power supply and this seems to like to let some of the factory smoke out of some of the (I believe) RS-485 chips(?)  I had another sitting on the bench, so I soldered it up (without the additional power connections) and utilized the same PC power supply and all worked well through the rest of the year. 


I appreciate your help in advance,

- Mark

Offline corey872

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Re: DLA Active Hub Failure
« Reply #1 on: January 08, 2017, 07:20:01 AM »
Good, detailed / high res pictures of the board often helps.  And it would be really good if you could id the actual components failing.

If everything was working fine, then died at some point later, that 'typically' means either water/moisture intrusion somewhere in the system, or some connection shorted somewhere.  It is possible, though much more rare for some component to just 'fail'.

If it is a 485 chip, those are basically just transceivers for the data signal.  Since that is a low volt / low power signal, there is not much way to actually 'smoke' the chip, though one possibility might be to dump a high current 12V source right on the data inputs or output.  So possibly look for any miswired or shorted 'power to data line' connections.  A solder bridge on the circuit board might be another option, but since you say it was working, then quit it would not be likely.

You might try troubleshooting with all outputs disconnected.  That would isolate the issue to the hub itself, or the attached elements.  If the board is the issue focus on it.  If it works with nothing attached, possibly re attach the outputs one a time to find the problem.
Corey
 2018 uSC, Afterburner, uAmp co-op - pending May-June 2018.  Remaining boards are now FOR SALE

Offline mkozik1

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Re: DLA Active Hub Failure
« Reply #2 on: January 08, 2017, 07:03:34 PM »
Hi Corey and thanks for the suggestions.

The board is actually housed inside and no moisture got on it.  The power supply used is showing to be good, not overpowering the board.  All of the testing I did WAS done with nothing connected in an effort to isolate the problem.  I am not sure if the images will come through, but I am going to give it a shot!!




Offline corey872

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Re: DLA Active Hub Failure
« Reply #3 on: January 08, 2017, 08:00:49 PM »
Images came through fine.  I don't see anything amiss in the 'usual suspects' category... chip inadvertently inserted backwards, flipped polarity on a capacitor (though a couple are hidden behind the heat sinks), solder bridges, etc.  Though again, as you say, the board worked at one point - so most of that would be unlikely.

It seems like the 'green light on then fade out' might have been an over current tripping on the original power supply and possibly the PC supply had enough power to push through that limit and burn some things up?  I don't see any chips obviously burnt - can you describe which ones seemed to smoke?

You say power supply is good and not overpowering - this is the original supply or the second PC supply?

Back to assuming the 485 chips are smoking, another possibility might be failure of the 5V regulator.  I believe the 485's are spec'd for 7V absolute max Vcc.  So if the 5V reg shorted and dumped 12V on that rail, it might have taken out the 485 chips and caused the original supply to shut down on over current.
   
For a next step, you might try pulling the smoking chips (at a bare minimum) or all socketed chips and going back to the aux power supply.  See if you can get it to turn on and stay on.  If so, probe the regulators and any other spots on the board looking for correct voltage.  If the supply still seems to shut down, I'd pull the 5V reg for a start, then try again.  Then move on to the 3.3V reg if that didn't work.

Offline mkozik1

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Re: DLA Active Hub Failure
« Reply #4 on: January 08, 2017, 08:12:35 PM »
Hi Corey,

I looked at this again tonight to see if I can tell exactly which component was causing the smoke when the PC supply is connected and it is so fine and slow that it is VERY difficult to see just where it is coming from.  I am not sure if it is from the chip or the regulator, but the area in red is where I am seeing it.  I tested some points on the board with the 12v power supply connected and the LED off seeing 12v in many areas which I thought it should be and it was good to go.  I checked the PC inputs finding good voltage there, around the RJ45 connectors, they are good and the monster resistor finding voltage there as well (and it was getting hot).  I also found 3.3 volts in a few spots but as you mention it below, I do not recall seeing 5v anywhere.  Other than the regulator, where else should I be seeing that?

Offline CaptainMurdoch

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Re: DLA Active Hub Failure
« Reply #5 on: January 09, 2017, 11:39:04 AM »
I thought that you weren't supposed to use the PC power inputs with the 12V option installed because the 12V option adds the 5V and 3.3V regulators where the PC power supply is also connected to those spots on the board, so powering via PC power supply is essentially feeding power into the output side of the two regulators.
-
Chris

Offline taybrynn

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Re: DLA Active Hub Failure
« Reply #6 on: January 09, 2017, 12:42:02 PM »
I thought that was true also ... either regular AC or 12v not both ?

Offline jnealand

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Re: DLA Active Hub Failure
« Reply #7 on: January 09, 2017, 01:02:29 PM »
I've wondered about that myself, but I have looked thru DLA and I have not been able to find any definitive info.  I've thought about adding the option to my boards just to give me a backup power device as I have more 12v PS than spare PC PS these days.
Jim Nealand
Kennesaw, GA all Falcon controllers, all 12v Master Remote Multisync with Pi and BBB P10 and P5

Offline mkozik1

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Re: DLA Active Hub Failure
« Reply #8 on: January 09, 2017, 01:12:37 PM »
So .... Two questions (and pardon my ignorance) 

1) If applying power via the PC connectors, would/could this cause smoke to be released on the regulators?  Or is it just a directional thing?

2) Would the next course of testing for me be to remove the option and test with the PC supply again?

Offline jbsquires

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Re: DLA Active Hub Failure
« Reply #9 on: January 09, 2017, 04:19:44 PM »
Yes to number two:  Remove the 3.3 and 5 volt regulators from the 12 volt option and re-test

Offline mkozik1

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Re: DLA Active Hub Failure
« Reply #10 on: January 09, 2017, 04:27:58 PM »
Oki Doki - Will do that this evening

THANKS for everyone's help thus far!

Offline corey872

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Re: DLA Active Hub Failure
« Reply #11 on: January 09, 2017, 06:07:10 PM »
...
1) If applying power via the PC connectors, would/could this cause smoke to be released on the regulators?  Or is it just a directional thing?

Guess I had not heard of the 'either/or' issue.  In a perfect world, it would not make a difference, though if PC supply were a bit higher voltage than the regulator output, the regulator would see it as a reverse current.  Depending on the type of regulator, that could be significant.

Either way, pulling the regulators is a good (but not easy) next step.  Sounds like the original power supply was shutting down for some (still unidentified ?) reason.

Offline tbone321

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Re: DLA Active Hub Failure
« Reply #12 on: January 09, 2017, 08:20:32 PM »
The problem was discussed a long time ago on DLA and the thought was that if you connected a PC supply with the regulators in place, unless the PC supply voltages were an exact match to the regulator outputs, they would fight and possibly overheat or cook the regulators. 

Offline mkozik1

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Re: DLA Active Hub Failure
« Reply #13 on: January 09, 2017, 08:22:26 PM »
Understand that I am NOT trying to use them both at the same time - I am only testing with one or the other to see what might be the problem.

Offline tbone321

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Re: DLA Active Hub Failure
« Reply #14 on: January 09, 2017, 08:39:37 PM »
That is unknown to the regulators on the board.  When you connect the PC supply, it is supplying voltage to the 12V, 5V, and 3.3V rails.  The onboard regulators see an input voltage and put out a regulated output voltage.  If the output voltage seems too high, it will sink some current to drop the voltage.  The problem is that when this happens, the PC supply will see the voltage drop and flow more current to bring the voltage back up which causes the regulator to sink more current, causing the PS supply to flow more and on and on it goes until something overheats and cooks.  If the voltage is too low, the regulator will flow more voltage to the output where the PC supply will see it and sink more current to bring it back down and again, it goes around and around until something maxes out or overheats.  The problem for the hub is that the PC supply is designed to output MUCH more current on both the 3.3V and 5V outputs than the hubs regulators can handle.

 

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