Couple of failed Vellman builds.

Discussion in 'The Projects Forum' started by AJS14, Feb 4, 2014.

  1. AJS14

    Thread Starter New Member

    Feb 4, 2014
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    My first two builds ever didnt work. One kind of functions and the other is dead under power. I didn't expect them to work but I had hope lol

    How do I troubleshoot these? I don't really care that they didn't work in fact I think its a plus. What I want to do is find the faults and learn from them. I dont see any shorts on the boards but Im new to all of this.

    Thanks in advance.
     
  2. bance

    Member

    Aug 11, 2012
    315
    34
    Hmmmm! let's get the crystal ball out......

    Maybe a little more information would help ;- )
     
  3. TANDBERGEREN

    Member

    Jan 20, 2014
    74
    4
    You could first tell us what projects it is.
    Then tell us what kind of problems you experience.
    Schematics and pictures is always a good help.

    And at last: How experienced are You? Have You ever built any electronics earlier?
     
  4. AJS14

    Thread Starter New Member

    Feb 4, 2014
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    Ok I guess we should do these one at a time. This is Vellman MK102 it is supposed to alternate light LEDs but it just lights up the one on the left.

    I do not have any previous experience building electronics. I want to build some noise box kits from Music From Outer Space and to that end I decided I need to become competent at assembling electronics from kits so I decided to get some interesting inexpensive kits to practice with.

    [​IMG]

    [​IMG]

    [​IMG]
     
  5. takao21203

    Distinguished Member

    Apr 28, 2012
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    this circuit is notorious to fail at random point of time or never to work at all.

    But also the LED could be broken, or soldered wrongly. The solder joints don't look perfect either, suggest to reheat all + add tin.

    LEDs can actually break from soldering quite easily- even with a lot of experience, I try to leave some distance (on the wire legs). If I have to solder them without a gap, some LEDs will always die from the heat.

    Your 9v battery could be empty- you need a DMM (digital multimeter), if you don't already have one. Make sure both LEDs work with the DMM continuity tester.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Tht's an astable and that was the first thing I ever build.

    But is the picture coloring or are all those 10K resistors.
    If that is the case it will never work.

    What I remember was
    1 . I did not use RV1 & RV2
    2. R1 & R2 are not needed ( but this was at 3V from 2 , 1.5V cells)
    3. R3 & R4 goes to Vcc.
    The rest are same. To vary the blinking we just swap the caps to higher values.
    The circuit would run for days.

    In your case at 9V you can lower the value for R1 and R2 for like 220Ω or 330Ω. 1KΩ is way too high for a RED LED at 9V.

    If the LED in not blinking then you need to decrease the VR values by turning the VR. Start with minimum value (VR all the way down)
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    If one LED lights up then that LED cap is charging too slowly, decrease all the VR to zero value. Don't worry it won't burn up anything

    Remeber if you decrease R1 & R2, the LED will light brighter and the switching speed will also be faster. But at 1K ur LED will just barely light. Right?
     
  8. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    It looks like only two of the three terminals for the pots have been soldered. Under the first "L" of Vellman and under the "a" and "n" of Vellman. Without the wipers connecte, the circuit has no chance of working.
     
    R!f@@ likes this.
  9. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Darn ! I missed tht. :mad:
     
  10. AJS14

    Thread Starter New Member

    Feb 4, 2014
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    I had concerns about these pads as well but what I built looks like the picture and it wasn't clear to me what these are for. The trimmers are soldered at three points is there a 4th point that needs to be connected?
     
  11. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
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    That PCB was designed to accept either horizontal or vertical trimmers.
    The traces from the un-soldered pads follow around to the soldered terminals.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Try adjusting the two pots (potentiomenters) so that they are centered; mid-way between either end. As it is now, it appears you have them adjusted to opposite ends.
     
  13. AJS14

    Thread Starter New Member

    Feb 4, 2014
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    thanks for suggestions Ive tried 9 combinations and several batteries. in all cases the left light shines but that's all I get. I think the lower right resistor (on the front) might be shorting onto the trace for the transistor. There i a big blob of solder on the back and it looks like it is on the trace for the transistor. Im going to assume it melted through the player covering the trace.
    Do I need a wick to draw solder off the PCB to resolder it?
     
  14. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    You can use solder wick or pump. Wick is better sometimes.

    Confirm what you have aren't all 10KΩ resistors cause from the picture it seems 10KΩ. As in orange band instead of red
     
  15. AJS14

    Thread Starter New Member

    Feb 4, 2014
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    Confirming that the bands on middle R are orange not red.

    I dont have any wick today. Im going to use some speaker wire and flux to draw the solder off.
     
  16. AJS14

    Thread Starter New Member

    Feb 4, 2014
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    EUREKA!
    SUCCESS!

    I used speaker wire and flux to clean some big blobs and I filled in some connections that looked bad to me. Now I have a working piece. Thank you all for your assistance. Having this forum as a resource has really helped me.

    I will post a new thread for the other device.

    Thanks again.
     
  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Glad to hear u got it fixed.
     
  18. AJS14

    Thread Starter New Member

    Feb 4, 2014
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    lol yeah Im hooked now.
     
  19. KJ6EAD

    Senior Member

    Apr 30, 2011
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    I'll throw in a couple of additional tips regarding Velleman kits.

    The copper pads are often lightly oxidized by the time you get to them so it helps to give them a light scrub with a Scotch Brite pad and wipe with alcohol before starting assembly. This will significantly improve pad coverage and solder wetting.

    Many of the Velleman kits use low current LEDs to conserve battery power so don't be surprised by higher than typical value limiting resistors.
     
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