What problems are in this board?

Discussion in 'General Electronics Chat' started by booboo, Sep 24, 2015.

  1. booboo

    Thread Starter Member

    Apr 25, 2015
    165
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    Hi
    I'm working on my board and today after assembling some components on it, I ran it and unfortunately sounds like some components burnt out. it's a question to me what cause these problems. this is the schematic:

    [​IMG]

    And PCB:

    [​IMG]
    Also I think one problem is that I have designed two 3v3 LDO for this board to have enough current. I think that was not a good idea. Is there any other problem/mistake in your opinion?
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,155
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    Any idea what might have burnt? Did you breadboard this before building a PCB?

    I'd start with divide and conquer. Isolate the various sub-circuits and see if they are still functioning. Check your regulators, check the operation of the iron control circuit. And so on. Look for simple mistakes like reversed components or wrong pinouts. It's often the stupid stuff that is the most difficult to overcome.
     
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  3. booboo

    Thread Starter Member

    Apr 25, 2015
    165
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    Hi Thanks for reply
    after checking the board I found out that the MCU has been died. what would make an MCU dead in my circuit? also the regulator of my LCD module made a big smok when I turned the circuit on for first time. this is my LCD module:

    [​IMG]

    I mean that black and three legs component.
     
  4. ISB123

    Well-Known Member

    May 21, 2014
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    Short circuit
     
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  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    has the cpu died? I see no supply connected to vdd.
     
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  6. booboo

    Thread Starter Member

    Apr 25, 2015
    165
    2
    Oh! sounds like you're right. because I checked my board by a DMM on beep(diode) mode and there is a short circuit. also I have not desoldered my MCU still.
     
  7. booboo

    Thread Starter Member

    Apr 25, 2015
    165
    2
    Yes, I made a mistake when I was designing the board. I figured it out just with one wire to 3v3.
     
  8. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    W1,2,3 & 4?
     
  9. booboo

    Thread Starter Member

    Apr 25, 2015
    165
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    They are jumper. I didn't connect them still.
     
  10. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    PCB critique: Long skinny snaking traces, especially on power rails and high current nets, can be problematic.
     
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  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    deja vu

    You already posted about shorts a few weeks ago.. Is this the same problem? Did you fix that problem?..
    Why would you assemble "some" components and then attempt to fire it up?
    Why don't you tell us which components are faulty or whats not working or something?
    Did the sub-circuit components of those faulty components get assembled?

    Only soldering "some" components could cause some circuits to not work at all while causing damage to others..
     
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  12. booboo

    Thread Starter Member

    Apr 25, 2015
    165
    2
    ?
    No, I figured it out.
    yes
    But I said.:rolleyes: the regulator of my LCD module and the MCU and much more probably regulator on the board.
    I cannot get it. what do you mean "sub-circuit components"?
     
  13. wayneh

    Expert

    Sep 9, 2010
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    He means what I suggested earlier - build and check the regulators, build and check some other function. Divide and conquer. Just like you would do if you plugged in a TV and it went poof. You start looking at the power supply and move downstream.
     
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  14. booboo

    Thread Starter Member

    Apr 25, 2015
    165
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    I thought the probelm is using two 3v3 LDO together then I removed one of those 3v3 supplies from the board and replaced the MCU and LDO with a new one. plugged in and BOOOOOM!:(

    There was not any short circuit on the board after replacing( now there is but I'm sure that's not the reason!). there is a problem on the board but I don't know what is it!:(

    For example?
    I cannot get this part. What do you mean?
     
  15. wayneh

    Expert

    Sep 9, 2010
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    I mean one step at a time. A complex system is very hard to diagnose, but is usually made up of smaller sub-systems. It is very much easier to, for instance, verify that each IC has power to it as expected. Yes? Then start checking the input and output pins of the IC. Sometimes you need to separate the sub-systems completely in order to verify they are working. I think I saw at least one transistor as a switch in your schematic. You can probe to see if that transistor is functioning as you need it to.
     
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  16. JohnInTX

    Moderator

    Jun 26, 2012
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    You don't say what the PN is but your two 3V3 regulators are not pinned like the SOT-223/DPAK stuff I am familiar with. The tab is usually GND. You show GND as where I would expect the input. Miswiring the regulators would account for what you are seeing.
    Also not sure about paralleling them.
    What is the PN of your regulators? Are they like any of these?
     
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  17. GS3

    Senior Member

    Sep 21, 2007
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    Sun Tzu? Is that you? Or am I confucius? ;)
     
  18. booboo

    Thread Starter Member

    Apr 25, 2015
    165
    2
    Sorry,
    It's AMS1117.

    [​IMG]
     
  19. pwdixon

    Member

    Oct 11, 2012
    488
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    I assume you didn't connect the lcd directly on the board connector ie. 1-1, 2-2 etc?

    Did you try powering the board without the lcd connected?

    Are both of the 3.3V regulator outputs connected directly together?

    Did you run any design rule checking on the pcb layout?
     
  20. booboo

    Thread Starter Member

    Apr 25, 2015
    165
    2
    Yes, I didn't.
    Yes. the last time.
    Yes, but I think I should to use two diode. because of this:

    http://electronics.stackexchange.co...-together-to-produce-higher-amperage-possible

    Also the last time I removed one of the LDOs from the board(+ it's capacitors).
    No, How can I it in the Altium?
     
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