7805 appears to not be working - any ideas?

Discussion in 'General Electronics Chat' started by PotatoClock, Apr 29, 2017.

  1. PotatoClock

    Thread Starter New Member

    Apr 29, 2017
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    This is a long shot but I wanted to try anyway. Over the past year I've been working on my A2 coursework. For part of it I had to design a circuit using Circuit Wizard 2.0. Designed it, went through everything, made the PCB, soldered everything in and ironed out the mistakes I made when I was doing that. Here's the hard part - For some reason the 0V rail is receiving around 7-8V. I can't find why this is happening, there is no connection to the positive, and I've checked for a stray wire or loose connection. I'm out of ideas on what it could be and so is my teacher. Also, in my class of 9, only one other person has their circuit working, all of the others have a myriad of faults for no apparent reason. Could it be that my school uses cheap components or have i made a mistake in designing my circuit? I replaced the original 7805 with another but same problem.

    In the post which led me to this website (link: https://forum.allaboutcircuits.com/threads/lm317-vs-7803.37268/ ) I saw that the capacitors needed were 0.33uF and 0.10uF. I was told to use 0.10uF capacitors for both, so could this be the problem? Any help at all would be hugely appreciated, thanks.
     
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
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    Welcome to AAC!

    Post a schematic of your circuit with relevant voltages marked.

    Your post would be easier to read if you used paragraphs...
     
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  3. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    So you've got one meter probe on the 0V but where is the other probe connected to when you're reading 7-8V?
     
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  4. PotatoClock

    Thread Starter New Member

    Apr 29, 2017
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    Really any component connected to the negative rail, I can have both meter probes on different legs of the voltage regulator and have the same result
     
  5. AlbertHall

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    OK, post good pictures of both sides of the PCB.
     
  6. PotatoClock

    Thread Starter New Member

    Apr 29, 2017
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    Yea sorry about that, doing this all in a bit of a panic

    Here's a screenshot of the PCB on circuit wizard. Sorry it's a bit blurry, best I can do. I'd upload the file but I can't when I try to. The circuit uses 9V battery and it all turns on in real life, it's connected to seven segment displays and they work, but the problem is that because of the positive negative rail, the PIC won't work, though strangely the 4026b's do
    upload_2017-4-29_19-51-39.png
     
  7. AlbertHall

    AAC Fanatic!

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    For a start D9 is the wrong way round.
     
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  8. Ford Prefect

    Senior Member

    Jun 14, 2010
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    I am interested with this. But the screenshot is not showing the full circuit. Did you design and build this on the PCB sheet of Circuit Wizard or did you design the circuit on the Circuit Design sheet and use the application to convert to a PCB?
    I think the answer is the former not the latter. But if you do have a schematic it will be easier to work out where the problem is. Can you post a schematic diagram?
     
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  9. AlbertHall

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    The attachment shows more/all of it
     
  10. PotatoClock

    Thread Starter New Member

    Apr 29, 2017
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    I designed a circuit schematic but had to manually design the PCB.
    upload_2017-4-29_20-16-18.png

    upload_2017-4-29_20-16-35.png
    upload_2017-4-29_20-17-0.png
     
  11. Ford Prefect

    Senior Member

    Jun 14, 2010
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    Oh yes thanks. I am using my telephone to read this and didn't notice the attachment. :D
     
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  12. AlbertHall

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    The circuit diagram you attached to post #10 does not match the PCB layout.
     
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  13. PotatoClock

    Thread Starter New Member

    Apr 29, 2017
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    I know, part of having to make the PCB manually (not my choice) was that things that worked with the circuit design wouldn't work with the PCB design, because I needed to keep the number of flying wires down
     
  14. dl324

    AAC Fanatic!

    Mar 30, 2015
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    Post a schematic that includes the voltage regulator and the voltages you're measuring.

    If you can't post a file, cut and paste the information.
     
  15. Ford Prefect

    Senior Member

    Jun 14, 2010
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    Agreed.
    At first sight I doubt if it has anything to do with the 7805 but certainly D9 is the wrong way round. I am suspecting that when you built this, a component or a wire connection is incorrect.
     
  16. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    IC1 (whatever it is?) seems to have some floating data inputs (D0, D1), and Q2 (an output?) is shorted to the +ve rail by the switch SW3.
     
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