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RG1 1.8v regulator

Former Member

Ok, so in a different thread I threatened to remove RG1 and do some current measurements on it's output after seeing those thermal images that show it's not generating any heat...

 

Well, I did it tonight. Some photos here: https://picasaweb.google.com/selsinork/RPi18v

 

The jumper pins in the output let me either just put a jumper on and verify the Pi boots ok, or wire a multimeter in series to get some current readings.

 

The results were interesting to say the least. I had to go back and check I was reading the multimeter correctly, that it wasn't broken etc.

 

On initial power up I see a negative current for a second or so which then reverses to about 0.5mA (yes half a milliamp, that's not a typo) for a few seconds while we get the first sd-card accesses. Once we're booted and sitting at the login prompt the current reading fluctuates from around 0.001mA to maybe 0.04mA. 

 

I'm using the 40mA range on a decent Fluke multimeter, so I've no reason to doubt the results. There's obviously going to be some inaccuracy down at that level due to length of meter leads etc, but the result is fairly clear.  You'll understand why I was checking the meter was working and I was reading it correctly though image

 

 

So from there onto the next test, lets try completely disconnecting RG1 and see if the Pi boots while using the LAN9512 1.8v 'output'.  Yes it does! 

 

I think that's reasonably good indication that jamodio got it spot on, the lan9512 shouldn't be connected to the 1.8v plane and it's heat problems are going to be largely due to supplying current on it's 1.8v filter pin that it was never designed to do.

 

So anyone willing to pull RG1 off a Pi and verify my results ?

Parents

  • Time keeps going by and I don't see any information being shared by Pete or anybody from RPF about the issues and what we can expect to get them fixed.

     

    -J

  • in reply to jamodio

    Jamodio,

      right, Pete has gone silent, and JamesH says he can't say much.

    Pete said he was in full-duplex communication with SMSC, but

    apparently he's not eager to share.

     

    People have asked for gerbers to see if there's a way to disconnect

    1.8v by drilling a hole in a strategic place, but no response.

     

    That doesn't mean progress isn't being made, such as people

    experimenting with heatsinks.   Maybe SMSC could be asked

    if the networking problems are a plausible result.  Maybe someone

    will use sandpaper to reveal exactly how the power is connected.

  • in reply to Former Member

    coder27 wrote:

     

    People have asked for gerbers to see if there's a way to disconnect

    1.8v by drilling a hole in a strategic place, but no response.

     

    I've seen people ask for gerbers just for openness on principle, but not for that specific diagnostic purpose.

     

    If that request was made in a place which RPF could not have missed, and they responded with silence, it's worse than I thought.  They don't even value help from their dedicated supporters.

     

    The Foundation is rapidly losing all the little credibility that's left.  What a bunch of self-centered and myopic incompetents.

  • in reply to Former Member

    Guys, everybody is blaming the 1.8V problem for the keyboard repeat problems. However, the source of the keyboard repeats has been found, and it is that USB interrupts are delayed more than 1ms. The cause for this is the SD card driver. That is why morgaine is now using an USB stick for his root.

     

    The kernel/sd card driver will be fixed in time. In parallel other people can fix the 1.8V problem, but I haven't seen a confirmed problem caused by this.

     

    The 0.15W extra power in the LAN chip will raise the temperature of the LAN chip by a few degrees. Maybe 10. This should be within range of what is allowable.

     

    Diagnosing "intermittent" problems is difficult. people see patterns way too quickly. You have to try with and without a few times and reproduce the problem consistently with one setup and not with the other.

  • in reply to rew

    Roger,

      I don't think the keyboard repeats problem is quite so well understood.

    User Max still reports problems with the Enter key.

     

    http://www.raspberrypi.org/phpBB3/viewtopic.php?f=28&t=12097&start=241

     

    If SMSC is telling Pete not to worry about the LAN chip, then he would

    probably be eager to share that. 

  • in reply to Former Member

    Coder, SMSC is NOT telling pete not to worry. Someone else asked SMSC and got told: "No way!".

     

    In some "circles", the understanding is that oscilations will result if you parallel two linear regulators. This is not always true. In many linear regulator datasheets they recommend the parallel setup for situations where you need up to 2x the current of just one of the regulators.

     

    With Pete's preoccupation with "sufficient decoupling", this means that I really don't expect any oscilations.

     

    SMSC says the regulator should not provide external current. Fine. But what happens if you do draw current? You might cause the SMSC regulator to drop into the "dropout" region. So it will be in "constant current" mode. So regulation is delgated to the RG1 regulator. Still the voltage will remain within tolerance.

     

    This means that the only problem is that 0.15W is dissipated in the SMSC chip, instead of the RG1. As said before.

     

    With "intermittend problems", and interrupt problems not completely fixed, I'm not too worried about the single report that mentions an enter-keyup event going missing.

Reply
  • in reply to Former Member

    Coder, SMSC is NOT telling pete not to worry. Someone else asked SMSC and got told: "No way!".

     

    In some "circles", the understanding is that oscilations will result if you parallel two linear regulators. This is not always true. In many linear regulator datasheets they recommend the parallel setup for situations where you need up to 2x the current of just one of the regulators.

     

    With Pete's preoccupation with "sufficient decoupling", this means that I really don't expect any oscilations.

     

    SMSC says the regulator should not provide external current. Fine. But what happens if you do draw current? You might cause the SMSC regulator to drop into the "dropout" region. So it will be in "constant current" mode. So regulation is delgated to the RG1 regulator. Still the voltage will remain within tolerance.

     

    This means that the only problem is that 0.15W is dissipated in the SMSC chip, instead of the RG1. As said before.

     

    With "intermittend problems", and interrupt problems not completely fixed, I'm not too worried about the single report that mentions an enter-keyup event going missing.

Children
  • in reply to rew

    It is not clear who is telling who what, but what is pretty clear is that we are not being told anything !!

     

    I strongly believe that at this instance the distributors should stop producing and selling the current revision of the board, which is clearly faulty.

     

    -J

  • in reply to jamodio

    jamodio wrote:

     

    It is not clear who is telling who what, but what is pretty clear is that we are not being told anything !!

     

    I strongly believe that at this instance the distributors should stop producing and selling the current revision of the board, which is clearly faulty.

     

    -J

     

    Jamodio,

      You are not the first to suggest this.

    On the RPi.org forum, user lajos wrote:

     

       "I hope this next suggestion won't be taken the wrong way... but would it make sense to tell buyers that these are known hardware issues, or even stop manufacturing and sales until they are fixed?"

     

    Amazingly, he hasn't been banned, belittled, or had the thread locked.

    So maybe the RPF is actually considering that.

     

    http://www.raspberrypi.org/phpBB3/viewtopic.php?f=24&t=14478&start=10

  • in reply to Former Member

    coder27 wrote:

     

    On the RPi.org forum, user lajos wrote:

     

       "I hope this next suggestion won't be taken the wrong way... but would it make sense to tell buyers that these are known hardware issues, or even stop manufacturing and sales until they are fixed?"

     

    Amazingly, he hasn't been banned, belittled, or had the thread locked.

    So maybe the RPF is actually considering that.

     

    http://www.raspberrypi.org/phpBB3/viewtopic.php?f=24&t=14478&start=10

     

    Don't get your hopes up too high.  While it would be nice to think that RPF have finally woken up to reality and will start being open and honest, precedent doesn't support this possibility very strongly.  Rather more likely is that convincing spin is proving more difficult to manufacture as the evidence accumulates.

  • in reply to morgaine

    Morgaine Dinova wrote:

     

    coder27 wrote:

     

    ...Amazingly, he hasn't been banned, belittled, or had the thread locked.

    So maybe the RPF is actually considering that.

     

    Don't get your hopes up too high.  While it would be nice to think that RPF have finally woken up to reality and will start being open and honest, precedent doesn't support this possibility very strongly.  Rather more likely is that convincing spin is proving more difficult to manufacture as the evidence accumulates.

    Maybe manufacturing spin is taking too much time and effort, so they decided to outsource it to China.  But it'll take a few months to get the process working. image

  • in reply to johnbeetem

    John Beetem wrote:

     

    Maybe manufacturing spin is taking too much time and effort, so they decided to outsource it to China.  image

     

    Gosh no, we only outsource the productive parts of manufacturing that create jobs, grow native production capability, and increase knowledge of technology among the population.

     

    None of that stuff is needed in the West where the biggest growth industry is litigation, where the USPTO's primary role is chilling innovation, where the media companies treat their audience as criminals, where states block science in education, and where governments' only interest in technology to keep their populations in observational prison.

     

    Spin is a key competency right here at home, and a necessary process in making a dysfunctional board brilliant.