Author Topic: Potential power issue with EthD  (Read 2595 times)

Offline txag2008

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Potential power issue with EthD
« on: June 29, 2015, »
I've used my EthD the past two years for my shows and it's worked fine.  This week I've decided to pull it out of storage and play with some lights. When I hooked up the etherdongle to power and cat5 to my computer/hub I have no lights on either the Magjack or the green LED on the board.

I've been noticed the 3.3v regulator was very hot. I can unplug the wallwart and plug it back in and within 10 seconds the 3.3v regulator is too hot to touch. I measured voltage from the wallwart and got 10.2vdc (this is from a co-op and the label shows it to be 6vdc.)

What is the best way to test the 3.3v and 5v regulators? I have a good multimeter but not sure which pins to test. Also, is this high of voltage typical from the co-op wallwart and is the EthD tolerant of it?
« Last Edit: June 29, 2015, by txag2008 »
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Offline tbone321

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Re: Potential power issue with EthD
« Reply #1 on: June 29, 2015, »
No, it looks like the regulator in the wall wart has failed.  Before going any further, you need to replace that wall wart with one putting out the correct voltage.  After that, check the voltage on both the 3.3V and 5V regulator and see if they are both functioning.  The fact that the 3.3V regulator is getting that hot is not a good sign.  If the 5V shorted out, it may have caused serious damage to the board. 
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Offline n1ist

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Re: Potential power issue with EthD
« Reply #2 on: June 29, 2015, »
Before you panic - linear wallwarts like this (just a transformer, rectifier, and filter cap; there is no regulator in there) show the approximate output voltage when fully loaded.  Unloaded, they will definitely read higher.  I just grabbed one from a Lynx wireless (rated 6V/300mA) and unloaded it measures 9V.  10.2V is probably correct for that one, as it is a 1A transformer.  As a matter of fact, RJ is counting on it being higher than 6V as the 7805 wants 7V or so minimum. 

Check the output voltages of the two regulators.  For the 7805, the center pin is ground and the right one (looking at the front of the package) should measure 5V.  For the 1117, the left pin is ground and the center pin or tab should be 3.3V. 

/mike

Offline txag2008

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Re: Potential power issue with EthD
« Reply #3 on: June 29, 2015, »
When plugging the wallwart in at first, the 1117 reads 3.7v but then begins to climb and got up to 4.8v before getting very hot and I unplugged the power.

 The 7805 read 6.2v at first but then began to climb and got up to 7.8v before I unplugged the power.





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Offline txag2008

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Re: Potential power issue with EthD
« Reply #4 on: July 02, 2015, »
Hate to be desperate, but any advice?

Is this indicative of a a failed wall wart?  Failed voltage regulators?
« Last Edit: July 06, 2015, by txag2008 »
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Offline txag2008

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Re: Potential power issue with EthD
« Reply #5 on: July 06, 2015, »
I just found the data sheet for my particular wallwart. You are not allowed to view links. Register or Login

It shows that an unloaded voltage is 10.2vdc. This makes sense now because I was measuring the plug of my wallwart with it unplugged from my EthD.  I just remeasured and when plugged in to the EthD I am getting 5.92vdc.

Initially I thought my power supply was bad, but with these new information it seems fine.


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Offline n1ist

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Re: Potential power issue with EthD
« Reply #6 on: July 07, 2015, »
Sounds like you may have a short on the 3.3v line.    Also, make sure you didn't swap the two regulators.
/mike

Offline txag2008

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Re: Potential power issue with EthD
« Reply #7 on: July 07, 2015, »

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Sounds like you may have a short on the 3.3v line.    Also, make sure you didn't swap the two regulators.
/mike
The two regulators aren't swamped since I've used this EthD in previous seasons just fine.

I just replaced the 3.3v regulator. I am now reading 3.4V and it increases to 3.8 before I unplug the power supply.  On the 5v regulator I'm reading 5.9v and it raises to 6.9v before I unplug the supply.

Is it a possibility that the capacitors coming right off of the power supply terminals are causing an issue?


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Offline tbone321

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Re: Potential power issue with EthD
« Reply #8 on: July 07, 2015, »
You should still check and clean the board.  Did you remove the EDT from its case?  What I am wondering is how you are exceeding the output voltage of the PS.  You said that you measured the voltage output of the wall wart under load and were getting 5.9V.  If that is the case, how are you getting 6.9V on the 5V regulator?  If you were really pushing close to 5V on the 3.3V side, there is a good chance for significant damage to the 3.3V components. 
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Offline txag2008

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Re: Potential power issue with EthD
« Reply #9 on: July 07, 2015, »
Yes the PCB is out of the case and I have inspected it over with no apparent signs of anything wrong.

I just took a minute to take some readings on the input side of the regulator.

Power supply loaded: 6.01v  (measures this for about five seconds after being plugged in and then starts to bounce around and begin to rise)

5v regulator
In: 5.98v
Out: 4.15v (measures this for about five seconds after being plugged in and then starts to bounce around and begin to rise)

3.3v reg
In: -.57v
Out: 3.51v (measures this for about five seconds after being plugged in and then starts to bounce around and begin to rise)

Obviously the things that stand out are the input voltage on my 3v regulator and the fact that both of my output voltages rise after initially being plugged in.



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Offline tbone321

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Re: Potential power issue with EthD
« Reply #10 on: July 08, 2015, »
These symptoms look a lot like the ETD may have been accidently been plugged into one of the hubs controller outputs.  If this is what happened, the magjack will need to be replaced.  If not, I would check your PS for AC leakage.
If at first you don't succeed,
your not cut out for sky diving

Offline txag2008

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Re: Potential power issue with EthD
« Reply #11 on: July 08, 2015, »
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These symptoms look a lot like the ETD may have been accidently been plugged into one of the hubs controller outputs.  If this is what happened, the magjack will need to be replaced.  If not, I would check your PS for AC leakage.
I guess that is possible, but even if the Magjack is damaged how would that effect the oddities in voltages I'm seeing at the regulators?  (I'm not trying to question you because I know you're much smarter about this stuff than I)

You mention AC leakage at the PS, I think my next step is to replace the PS since my latest measurements showed the voltage at the board bouncing around after being plugged in for a bit.
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Offline tbone321

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Re: Potential power issue with EthD
« Reply #12 on: July 08, 2015, »
The magjack will be damaged if it gets 12V on some of its pins.  The problem with silicone components is that when damaged, sometimes they open up and sometimes they short out.  If the magjack shorted out, it may be what is putting such a huge load on the 3.3V regulator and since the 3.3 is fed from the 5V regulator, it will put a high demand on it as well.  The condition that you are seeing appears to be what is called thermal runaway but I'm not sure what is changing.  It could be that the overheating regulators are beginning to allow more voltage which allows more current which gets them hotter, causing them to allow more voltage and on and on it goes.  I would remove the magjack and power up the board and see if the 3.3 still overheats.  If not, then you know what needs to be replaced and hopefully, the excessive voltage from the overloaded 3-3V regulator didn't damage the PIC's.  Remember that the green LED is not a power LED, it is an indicator that the EDT is operating properly.  If the magjack has failed or is removed, it will not light so don't worry about that one until the magjack has either been replaced or proved to be ok.
If at first you don't succeed,
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Offline txag2008

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Re: Potential power issue with EthD
« Reply #13 on: July 08, 2015, »
Thanks so much for the help so far.  I have an update from this evening.

Removed magjack and saw the same exact errant readings as before at both regulators. I then removed the 3V regulator and then the power supply was reading 9.3v (I assume it's higher cause it's less loaded?) and the 5v regulator read 9.3v at input and exactly 5v output. I then put a new 3V regulator back on and now I'm measuring the same errant voltages as before.


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Offline tbone321

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Re: Potential power issue with EthD
« Reply #14 on: July 08, 2015, »
Well, that shows that there is a short on the 3.3V side.  As Cory suggested, I would post a clear and well lit close up picture of the front and back of the board so that we can take a look at it. 
If at first you don't succeed,
your not cut out for sky diving