Power problems

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  1. - 28th July 2008, 22:34 #1
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    Well, I really dont know what do more.
    On the test board everything was ok. The LED was blinking, the LCD shows the numbers.
    Now I wrap it again and it aint work, unless I touch the 8Mhz crystal with my hand ;-0
  2. - 28th July 2008, 22:43 #2
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    And ofcourse, if using the programmer power , everything is ok (with MCLR stright to the +5v)
  3. - 29th July 2008, 03:44 #3
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    Quote Originally Posted by menta View Post
    Well, I really dont know what do more.
    On the test board everything was ok. The LED was blinking, the LCD shows the numbers.
    Now I wrap it again and it aint work, unless I touch the 8Mhz crystal with my hand ;-0
    That usually indicates a missing ground and/or pullup or pulldown somewhere, likely on MCLR, or missing cap's between Vdd and Vss (both pairs and across the pairs).
  4. - 29th July 2008, 05:31 #4
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    Look at the grounds. Make sure they are very nice, short, and fat traces (or wires). The traces (or wires) from the crystal to the PIC should be as short as possible. The capacitors on the crystal should also be as close as possible to the PIC, with direct connection to GND. Pay good attention to the MCLR connection (follow the datasheet, they did not went through all that trouble for no reason).

    This is what I tried to explain before. The 877A has external MCLR and external oscillator (the 887 has the capability to run both of them internally - not good comparison).
  5. - 29th July 2008, 08:53 #5
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    How do you explain that when using the power from the programmer, everything is OK ?
  6. - 29th July 2008, 13:38 #6
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    Quote Originally Posted by menta View Post
    How do you explain that when using the power from the programmer, everything is OK ?
    The programmer may hold MCLR low while Vdd comes up and release MCLR after a few milliseconds. Put a 'scope on it and see if you can see anything.
  7. - 29th July 2008, 18:39 #7
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    I'm not using all programmer legs, just + and -
  8. - 29th July 2008, 19:18 #8
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    Just for giggles.

    If you do not have a scope or frequency meter. Use you DVM set for AC and se what the the voltage is from the programmer vs the out put of the 7805.

    If you can measure frequency the take that measurement.
    Dave
    Always wear safety glasses while programming.
  9. - 29th July 2008, 21:59 #9
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    Its amazing,
    When I use the test board (http://dj-gil.com/PIC/posts/math.jpg) everything is ok.
    When I put in the wireWrap board (http://dj-gil.com/PIC/posts/WW1.jpg)
    (http://dj-gil.com/PIC/posts/WW2.jpg) its not working.
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