For Experets only: MCU is not Starting Up

Discussion in 'Embedded Systems and Microcontrollers' started by Razi.Raslan, Aug 26, 2014.

  1. Razi.Raslan

    Thread Starter New Member

    Aug 26, 2014
    1
    0
    Hello,
    I have a control board for an industrial washing machine...
    The controller is based on MCU + 2 Lines×16 Character LCD + SRAM + Keypad + relays...
    the MCU is H8/3003 running at 11.0592 MHz high speed crystal.

    Problem:

    • When powering up the board, nothing appears at display and at rare time some garbage charters may appear

    Primary Inspection:

    • LCD found to be faulty... replaced with a new one
    • all power capacitor where replaced with new ones. 5V is 5.0 DC
    • Crystal where replaced with new one and exactly with the same type and rating
    • Load capacitor also were replaced with the same value and type (22pF)

    Results of the Inspection:

    • Still the MCU is unable to start up... only rare times is able to do it
    • if I put my finger at one pin of the crystal, the MCU will start up and the display started to show texts...


    Some Hints:

    • if we back to the MCU datasheet, when find the load capacitor values could be at range of 10 to 22 pF
    • I have tried many pairs of loading capacitors' values such as 10, 12, 13, 18, 20, 22, 33 and 36 pF but nothing changed.


    Question:

    • What is going on with the MCU and the crystal??
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    Wich MCU are you using?
    How is oscillator setup in the program?

    Bertus
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,392
    1,606
    A schematic is essential if you want a meaningful answer.

    A picture of your build may also help, if you can get close enough to see details.

    "garbage charters may appear" is actually a very positive sign, I believe you have to have good code to init the display, though the delays may still need tweaking.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,553
    2,375
    It is not being held in Reset is it?
    Max.
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,792
    948
    examine the MCU pins for solder joints that are gray or have white frosty appearance. post a pic if you can.
    Try reflowing the solder connections if possible.
     
  6. jjw

    Member

    Dec 24, 2013
    173
    31
  7. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
    764
    How do you know that the LCD is faulty?
     
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