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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

  • As shown in Troy Mackay's post on Jul 28 it seems to me that we could mod our PI's to work more as the chips were designed.

     

    I think that this could make the PI more stable, from the looks of it.

     

    I am not a designer Just an old tech, but I think we need to find a way to FIX what we now know is an error in the board.

     

    So could someone do some practical testing to see if there is something that can be done to easly fix the current board, rather than wait for RPI foundation to fix it by waiting for a board redesign?

  • in reply to electron2

    i will love to try out the hack Troy mackay has done also and then test again with that fix on the board, but i have looked into this and i most say it is very well done by Troy as i think it is to small for me todo and i done have an microscope as need for this.

     

    so yes if some one can findout where to make an cut to split the LAN9512 1v8 from the lod 1v8 then i will try this also.

     

     

    Tooms

Reply
  • in reply to electron2

    i will love to try out the hack Troy mackay has done also and then test again with that fix on the board, but i have looked into this and i most say it is very well done by Troy as i think it is to small for me todo and i done have an microscope as need for this.

     

    so yes if some one can findout where to make an cut to split the LAN9512 1v8 from the lod 1v8 then i will try this also.

     

     

    Tooms

Children
  • in reply to Former Member

    It would help to have a nice set of Gerber files with the current pcb layout to take a look a the traces and vias to chose what is the best course of action

    before cutting stuff.

     

    One option could be to just lift the two VDD18CORE pins, put togeher a small board that can be placed on top where the logo is with the 3.3 and 1.8

    swtiched regulators, there are some very efficient and small ones like the LMZ10501 that can handle up to 1A and includes the FET and inductor

    on the chip, add the decoupling caps for VDD18CORE on this board and run a wire to those pins. With some work you could manage to have

    through hole pads to match the pads for the existing regulators.

     

    I think there are two or three tiny ceramic caps that will get hidden under the add-on board. It may work ...

     

    My .02

    -J

  • in reply to Former Member

    Tooms wrote:

     

    i will love to try out the hack Troy mackay has done also and then test again with that fix on the board, but i have looked into this and i most say it is very well done by Troy as i think it is to small for me todo and i done have an microscope as need for this.

     

    so yes if some one can findout where to make an cut to split the LAN9512 1v8 from the lod 1v8 then i will try this also.

     

     

    Tooms

    The microsope is really handy (and didn't cost me a cent), you'd be surprised what you can do when you can see what it is you are doing. I haven't even done a lot of SMD work. I'd love one of those IR cameras though... They'd be a bit harder to find in someones junk bin.

  • in reply to Former Member

    I really don't know how much effort to put on modifying the existing boards, what should happen is the RPF people acknowledge the problem, come up with a workaround, fix it for future boards and analyze the long term effects of THEIR ERROR.

     

    Don't think anybody will be open to a massive recall, but the right thing to do is TO FIX THE ERROR.

     

    My .02

    -J

  • in reply to jamodio

    For $38 I don't expect a great deal of support, but I do expect that for a first revision board shipped naked without accessories or a case in limited numbers that it was never intended for the classroom in this form. More likely their target was developers and hackers to help mature the product, find bugs and develop software. I would hope that there will be future revisions, debugged, upgraded, shipped with a case and basic accessories, but I'm happy to tinker about with what I have; that is, after all, what I bought it for.

  • in reply to Former Member

    Well they missed the target for about couple of million miles. At the development phase price is irrelevant, and on the production phase what matters is cost, and not just components and assembly, you have to factor in that you will also need people and systems if you pretend to do a professional and serious job.

     

    Being a charity or non-profit doesn't mean you have to cry all the time about it, I'm associated with non-profits that deal with huge piles of money and have a full time staff to do the organization's job to deliver on their mission and goals.

     

    I think the argument "you get what you paid for" is very lame, I really don't care much about how much I paid for it or even if I had to pay much more to be part of what was promised to be an initiative to improve education on computer science.

     

    There are no clear indications that there will be future versions or revisions and trying to obtain any information on that front is almost impossible. The only thing they keep talking about is the model "A" which is the same thing less few components and the camera module.

     

    Still is a nice gadget to play with eLinux.

     

    -J

  • in reply to jamodio

    jamodio wrote:

     

    the right thing to do is TO FIX THE ERROR.

     

    My guess is that fixing the error(s) is ongoing right now, and that this is why Pete has returned to the job.

     

    There's total silence from RPF about it only because they can't yet figure out how to spin this into "Our perfect and faultless design is now even more perfect and faultless!".  But I'm sure that Liz will find a way.

  • in reply to jamodio

    jamodio wrote:

     

    There are no clear indications that there will be future versions or revisions and trying to obtain any information on that front is almost impossible. The only thing they keep talking about is the model "A" which is the same thing less few components and the camera module.

    Ironically, the Model A fixes the 1.8V regulator problem by not populating the LAN9512 image, which also allows RasPi to run in a closed plastic case w/o heat problems.  Moderators at the RasPi Forum like to point out that the BCM2835 is used in cell phones without heat problems.  I don't recommend asking them how many cell phones have LAN9512 chips.

  • in reply to morgaine

    It was a good sign that Pete briefly showed up around here and somehow noticed and acknowledged that there are problems, but I'm not quite sure how much leverage he has.

     

    On the thread he showed up and mentioned "the list," I asked about "what else is on the list?" and the only thing I got so far is white noise.

     

    I already gave up trying to understand or figure what is going on with RPF, got tired of the default reaction and answer that "if there is something wrong with the Rpi the problem is YOU".

     

    -J

  • in reply to johnbeetem

    John Beetem wrote:

     

    Moderators at the RasPi Forum like to point out that the BCM2835 is used in cell phones without heat problems.

     

    The moderators live in a fanboi partition of reality where facts are an inconvenient irrelevance.  The BCM2835 is not known to have been used in anything other than Roku 2 until the Pi, and no BCM28xx series VideoCore has ever been used in a cellphone.

     

    It's the same odd partition of reality in which the Pi is called a "low power consumption" computer, the same "low power" that caused plastic components in that balloon payload to melt, and the same "low power" that doesn't allow me to keep my finger on the LAN9512 for longer than reflex time.

     

    Pity that XKCD isn't too interested in us.  There's enough material here for volumes.

     

    Morgaine.

  • in reply to Former Member

    Troy,

    You wrote:

    "More likely their target was developers and hackers to help mature the product, find bugs and develop software."

     

    I think that is a widely held misconception.  Liz has explicitly said the

    product is not in beta test.  Eben has explicitly said it is for sale to

    anyone, not just developers and hackers.  If they were wanting to

    find bugs and mature the product, they would have a highly visible

    bug tracking system, and they would be eager to hear complaints. 

    Instead they ban people who complain, labelling them "concern trolls". 

    Jamodio ought to be a hero on the RPi forum for finding what is probably

    the most serious design error.  Instead, he is banned as a concern troll.

     

    JamesH has made clear that they have no intention of disclosing

    defects to potential buyers, and Abishur banned the guy yesterday

    who advocated disclosing the known USB problems, and who said

    he wouldn't have bought his RPi had he known.  Certainly they don't

    show even the slightest bit of sympathy for those who end up

    feeling duped.

     

    So my impression is that their target market is the unsuspecting

    buyer who is blinded by the low price.  I think they are afraid that

    their sales would dry up if they disclosed that the product isn't finished,

    and they seem to think that they can't afford to lose the sales to those

    who end up feeling duped.