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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

    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?

    I think we'd all like an easy fix, but with the information we have available today what Troy did is likely the best we can do. Cutting three tracks and some fiddly at best soldering on of some wire links isn't for everyone though.

     

    Beyond that we need to wait to see what Pete comes up with.  If the full gerbers were available someone would have a look and see if there was an easier way to seperate the lan9512's 1.8v from the rest of the board, but even then from what the schematics suggest there's probably a 1.8v plane on layer 5 which could make it essentially impossible...  If we're very lucky there might be a single via in a favourable place that could be carefully drilled out, but that's just about as bad as Troys wire links.

     

    Tooms idea of a marginally higher 1.8v feed from an external switching regulator may be the simplest after-market mod to accomplish even if it's not ideal. There seems to be a fair bit of interest all round in replacing the linear regulators, several designs have surfaced already.

Reply
  • in reply to electron2

    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?

    I think we'd all like an easy fix, but with the information we have available today what Troy did is likely the best we can do. Cutting three tracks and some fiddly at best soldering on of some wire links isn't for everyone though.

     

    Beyond that we need to wait to see what Pete comes up with.  If the full gerbers were available someone would have a look and see if there was an easier way to seperate the lan9512's 1.8v from the rest of the board, but even then from what the schematics suggest there's probably a 1.8v plane on layer 5 which could make it essentially impossible...  If we're very lucky there might be a single via in a favourable place that could be carefully drilled out, but that's just about as bad as Troys wire links.

     

    Tooms idea of a marginally higher 1.8v feed from an external switching regulator may be the simplest after-market mod to accomplish even if it's not ideal. There seems to be a fair bit of interest all round in replacing the linear regulators, several designs have surfaced already.

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