Need help figuring out if Tegra is shorted

Discussion in 'Switch - Console, Accessories & Hardware' started by B_N_B, May 6, 2019.

  1. B_N_B
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    B_N_B Member

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    May 6, 2019
    Hungary
    Hi All,

    I have a dead Switch and after going hunting for shorted components, I found a couple with relatively low resistance to ground (lowest being 42 ohms).
    Please see picture attached with the capacitors and inductors that are showing continuity on my multimeter.

    In addition to the highlighted components having low resistance to ground, some of the capacitors around the tegra dye are also giving me around 42-45 ohms as well as the 3 phase buck regulator capacitors next to the wifi/bluetooth chip.

    Could someone with experience and/or a working Switch tell me if these are normal readings?

    Thanks a bunch
     

    Attached Files:

  2. Pintglass

    Pintglass GBAtemp Regular

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    Jan 28, 2019
    United Kingdom
    See attached image tests done with black probe on ground.

    switch mobo1.
     
  3. B_N_B
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    B_N_B Member

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    May 6, 2019
    Hungary
    Cheers Pintglass!

    You are a star

    The weird thing is, I have another broken switch and I get nearly identical readings. I reckon the chances of them having the exact same fault are slim.
    Both were manufactured in October 2016, so maybe the components used on mine are slightly different from yours?

    Would you by any chance happen to know what voltage runs across the cap that you highlighted?
     
  4. Pintglass

    Pintglass GBAtemp Regular

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    Which one are you referring to, i highlighted a few.

    — Posts automatically merged - Please don't double post! —

    @B_N_B

    Could you test this cap for resistance to ground on the soc for me please

    switch10.
     
    Last edited by Pintglass, May 8, 2019
  5. mattytrog

    mattytrog You don`t want to listen to anything I say.

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    What readings are you getting from MAX77620? Is it putting anything out?

    Have you ruled out M92T36 & BQ24193? Or maybe the MAX77621 bucks too? Though unlikely...

    Finally, pi3usb?
     
  6. disco2001

    disco2001 Member

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    Jul 21, 2011
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    hello
    on my non working switch resistance is 0.6 hom at the two side (0.6 = 0)
    so why a CAP ???

    unit is BSOD
    RCM is runing
    paylod seem to hang when trying to use sdram
     
  7. mattytrog

    mattytrog You don`t want to listen to anything I say.

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    Yep. I have a similar unitfrom someone on here. It is a proper headscratcher.

    Testing, I have found that the MAX77620 is dropping voltage somewhere.

    I`ve been through everything... All passives - yes ALL. BQ24193, M92T36, PI3USB, wifi/bt. Replaced RAM modules...

    I`m waiting on a replacement MAX77620 turning up. That is my diagnosis at the moment.
     
  8. B_N_B
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    B_N_B Member

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    I was referring to the cap you marked with the red arrow.

    I'll test the cap when I get home on the weekend.
     
  9. gamesquest1

    gamesquest1 Nabnut

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    try pressing down on the ram, i had a blue screen console and the board was slightly warped pressing down on the ram would allow it to boot normally, but without pressure on the ram it would either just stay on a black screen or boot to a blue screen immediately, and very very rarely boot successfully but freeze after a few minutes
     
  10. B_N_B
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    B_N_B Member

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    May 6, 2019
    Hungary
    Hi mettytrog, thanks for chiming in.

    So on broken switch #1, I have a suspicion it's the M92T36.
    - As per one of yours posts, I measured the voltage on pin 5 (2.85v) and 6 (nothing) and this leads me to think it's the M92T36
    - the 5v rail from the usb is there
    - the battery is not charging
    On the other hand, the MAX77620 does not appear to be outputting 1.8v so I cannot rule this IC out either. (although the M92T36 could be at the root of this too)
    I'm trying to source a cheap IC's at the moment.

    Broken switch #2
    - battery charges
    - MAX77620 outputs 1.8v
    - M92T36 pins 5 and 6 are outputting the right voltages
    I have no idea yet what the problem with this one is.

    I haven't quite figured out the dependencies between the IC's.
    Does the M92T36 feed the BQ24193 and MAX77620? (yeah.. I'm a noob but you gotta start somewhere)

    Thanks for your input
     
  11. mattytrog

    mattytrog You don`t want to listen to anything I say.

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    Usb-m92t36-max77620-bq24193
    ---------------------bq24193 depending on i2c commands etc
    I've purposefully left out pi3usb and the SoC control
     
    Last edited by mattytrog, May 9, 2019
    B_N_B likes this.
  12. mattytrog

    mattytrog You don`t want to listen to anything I say.

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    Also, drown both ram chips in flux (no-clean obviously, non corrosive) and reflow. About 370 degrees for a good 5 minutes including heat up and cool down.

    You won`t remove them easily so don`t worry... The groundplane absorbs a lot of heat.
     
  13. B_N_B
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    B_N_B Member

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    And the bucks are controlled by the max77620?
    What voltage are they supposed to output?
     
  14. mattytrog

    mattytrog You don`t want to listen to anything I say.

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    1.8v

    — Posts automatically merged - Please don't double post! —

    If I remember correctly, the bucks aren`t i2c controlled. Just a discrete enable/disable pin. I`ll have to double check my notes to confirm.
     
  15. The Real Jdbye

    The Real Jdbye Always Remember 30/07/08

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    Alola
    He could still desolder/move any components around them :P
    5 minutes sounds like a lot. Enough to damage something.
     
  16. mattytrog

    mattytrog You don`t want to listen to anything I say.

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    By time its heated up and cooled, it will probably only have 2 or 3 min of heat. Low speed hot air, nothing "should" dislodge due to surface tension of the molten solder. Its the best way of fitting QFN chips actually... They will "straighten" themselves up (within reason).

    If things are being blown off, that is either too much heat, too quickly or too much air.

    My experience anyway...

    When soldering 0201 and smaller, I always solder component to something (stiff copper wire or stanley blade on one side) then tack the other side to PCB - desolder your "blade" from other end and flux / reflow... Gives a really nice job.

    Did one last week, M92T36 area was bare apart from the chip itself during repair. Also, the ROHS lead-free crap needs a nuclear reactor virtually to get any decent flow on it.

    Why they did away with leaded solder is beyond me. How many people here have ever sat down and eaten a PCB for lunch?
     
    Last edited by mattytrog, May 9, 2019
  17. B_N_B
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    B_N_B Member

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    May 6, 2019
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    Hi Pintglass, the cap appears to be shorted to ground.
    Have you come across this fault before?

    Although I'm not sure if this short has anything to do with e.g. the battery not charging.

    Thanks
     
  18. Pintglass

    Pintglass GBAtemp Regular

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    Jan 28, 2019
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    Sorry no that cap's not to do with charging I was just curious as to why it gives low resistance.

    Have you changed bq24193 to rule out charging issue's.
     
  19. serko

    serko Newbie

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    Jun 12, 2019
    Turkey
    Hi B_N_B
    Did you figure out what the problem is? I have exactly same problem and my switch is dead:cry: Thanks,
     
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