Blinking green LED?

Hardware related problems and workarounds

Re: Blinking green LED?

Postby bszente » Sat May 24, 2014 9:58 pm

9600 wrote:but thought this needed stating for the record, as there will be those who are not familiar with the risks and we'd like to grow the community and not prune it :)

True. Thank you Andrew for pointing this out.
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Re: Blinking green LED?

Postby vdasfbtg » Mon Jun 02, 2014 8:21 am

I am also getting a blinking green LED with both power supply I received. I'll try to replace the capacitors.
Regards
-Valentín
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Re: Blinking green LED?

Postby Bikeman » Mon Jun 02, 2014 3:10 pm

Hi!

Just a question but is it actually demonstrated that the capacitors themselves are the root course of the failures? Sure they are bulged in the defective units, but that doesn't exclude the possibility that there's something else wrong with those PSUs which causes perfectly normal capacitors to fail after some time....I really don't know whether I would feel comfortable running those PSUs even with replaced capacitors.

HB
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Re: Blinking green LED?

Postby bszente » Mon Jun 02, 2014 3:54 pm

Bikeman wrote:Just a question but is it actually demonstrated that the capacitors themselves are the root course of the failures?

Capacitors do bulge due to heat, usage or using them out of spec but they do this in time. Not from one day to another but in months. They absolutely do not bulge just by sitting on the shelf. So this leads to 2 possibilities:
  • either the PSUs have been used, so they are not brand new
  • they were originally made with a faulty capacitor batch
We can exclude the first one, because the PSUs did not shown any sign of usage. So only the second option remains. Add the recall info to this (what you have find out), and all will makes sense. So the 2 capacitors did not bulge due to faulty electronics inside the PSU. The PSU was not used at all. The manufacturer used some very low quality capacitor batch. That's all. I would say, they were already bulged when the PSUs were manufactured.

But to answer your original question: at my workplace we checked the output voltage with an oscilloscope with the board powered on and it was steady 5V, no spikes, smooth line. So yes, it is safe to use (at least from my point of view).

With faulty capacitors, before opening the PSU the scope showed very sharp spikes on the output voltage without any load. Under load the reset circuit entered in the play -> the output voltage oscillation between 0 and 5V. This is how we found out the filtering capacitors were dead. We opened it and... you saw the picture :-)

I tell you my experiences with a "high quality" original brand (very good name in industry) mobile car charger that had short circuit directly from the plant (it was not just a manufacturing error, it had a very idiot design, with very high chance to cause internal short circuit due to the incredibly stupid internal cable routing). It burned out my car's fuse instantly :-) Fortunately the charger was easy to fix. Now I trust it better, than a new one, because I know it cannot happen again. The thing is: what you fix, you know it is done, you know what to expect. Otherwise it is just an unknown blackbox :-)
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Re: Blinking green LED?

Postby ARHILL999 » Tue Jun 03, 2014 2:13 am

After using the device headless I decided to try a blue tooth adapter on the USB port. When I tried to power it up I now get the dreaded blinking green led. As noted the power supply led also blinks. I have tried several other 3A power supplies and they all behave the same way. It puzzles me why there is no mention of what the blinking means. Someone noted the power is being reset. What is resetting it and under what conditions does this happen. I am comfortable in stating that my power sources are not the problem. I am going to clear the file systems logs and see if anything gets written. If I let it run, the FPGA gets hot but nothing seems to be running either through the Video or Internet.
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Re: Blinking green LED?

Postby bszente » Tue Jun 03, 2014 7:55 am

ARHILL999 wrote:It puzzles me why there is no mention of what the blinking means. Someone noted the power is being reset. What is resetting it and under what conditions does this happen.

Actually I wrote several times in this thread what that "blinking" means: repeated RESET of the PSU under high load (i.e. short circuit or over the spec current consumption). "Blinking LED" is an unfortunate name, because you assume some kind of error code signaling, but no: the board just keeps resetting because the PSU's protection circuit cuts the current to prevent short circuit. Just measure the voltage on the board's power connector, you will see 0V and +5V constantly changing with the frequency of the "blink".

So to sum it up: when you connect your board with the bluetooth the startup current is higher than without the dongle. If this starting current (Inrush current) is higher than what your PSU's can provide, the PSU will cut everything, hence the "blinking" which is actually a reset. The control electronics in the PSU "detects" this high starting current as a short.

The output filter capacitors (those two bulged capacitors) help in remedying this. Either:
1. Your official parallella PSU has capacitors that are starting to bulge, thus it can provide smaller inrush current which is enough for the board without bluetooth dongle.
2. Your other PSU's have the same situation like 1., or by design they have smaller inrush current.
3. Your dongle has shorts (I would exclude this).

If a PSU is rated 3A, that does not say anything about the supported inrush current. To "debug" your issue, you can try your board with normal ATX computer PSU, that can handle higher currents and see if the board comes up as expected. The red wire is +5V and black is ground from legacy harddisk power connector for example, but attention: the ATX power supplies do not start on their own, so the computer must be turned on.

And the necessary disclaimer: Take extreme care to not short anything in you computer case or on your Parallella board. Do it on your own risk, I do not take any responsibility if you damage anything or if you hurt yourself. :!:
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Re: Blinking green LED?

Postby FHuettig » Tue Jun 03, 2014 5:13 pm

bszente wrote:To "debug" your issue, you can try your board with normal ATX computer PSU, that can handle higher currents and see if the board comes up as expected.


I would strongly advise against this. Using any power supply rated 4A or more risks blowing the 4A fuse on the board (NON-resettable) and then you're toast until and unless you can replace the surface-mount fuse. An ATX supply might be able to push 20 to 40A, it might be an effective debug tool but only if the thing that melts was the problem and not just something between the supply and the problem, like traces on the board. A normal Parallella starts up with fairly low current, half an amp or less, because the FPGA is clear and one Arm core is shut down while the other one is only fetching code from the flash memory. While there will be some inrush current due to the bulk capacitors on the board, that will not be much. If the bluetooth dongle follows the USB requirements it will not draw more than 100mA on startup, with limits on how much capacitance they can put on the bus power too in order to limit the inrush.

In short, a properly-operating power supply rated at 2-2.5A or more should have no problem powering a properly-operating Parallella plus a properly-operating USB peripheral. If that doesn't work then something is significantly wrong. If the problems started when the dongle was added I have to suspect the dongle, or else it's a coincidence that the supply failed just when the dongle was added. But the first sanity check (presumably already done) is to remove the dongle and see if things go back to the way they were. Being able to measure the current would be helpful too.
-- Fred -- Hardware Guy --
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Re: Blinking green LED?

Postby bszente » Wed Jun 04, 2014 6:50 am

FHuettig wrote:Using any power supply rated 4A or more risks blowing the 4A fuse on the board (NON-resettable) and then you're toast until and unless you can replace the surface-mount fuse.

If there is a real short somewhere, which of course can be (let's hope it is not). But yes, you are right, it is better safe than sorry. The thing is, I started with the following assumptions:

1. The board was used successfully headless until now
2. The board was used successfully with other USB peripherals (like keyboard or mouse)
3. ARHILL999 does not use a broken dongle, i.e. the dongle is/was used successfully with other computers as well

Anyway, I think it is important to find out point 2 and 3 as well, but ARHILL999 please follow FHuettig's advice.
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Re: Blinking green LED?

Postby mercimek » Tue Jun 24, 2014 8:31 pm

@bszente: Hi, that’s true that the sometimes manufactures use the low quality capacitor batch and we can find it with oscilloscope but I am wondering is there any other way to test the capacitor especially with the multimeter?
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Re: Blinking green LED?

Postby svidgen » Sun Jul 20, 2014 12:57 am

I've emailed support@adapteva.com several times regarding the PSU. (Someone mentioned sending replacements.) But, I haven't gotten any indication that my email was received.

What's going on?
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