Lockout buzzer circuit

Discussion in 'The Projects Forum' started by Stargate_to_Earth, Jan 24, 2008.

  1. Stargate_to_Earth

    Thread Starter New Member

    Jan 24, 2008
    2
    0
    I recently bought a simple system from
    http://www.electronickits.com/kit/complete/game/vemk133.htm
    and just finished soldering it and only the middle two lights worked correctley and one of the buttons made both lights come on but not stay on and the other only made the controll light blink a little... then i tried to fix some of the soldering to make it work but all that did was make it not work at all :(

    heres the directions/schematics...
    http://www.electronickits.com/kit/complete/game/VEMK133.pdf

    my dad has a volt meter but i really dont know how to check it out...

    i am trying to make this system for my schools high-q team (College/Quiz bowl) (were poor and cant afford professional ones) and i planed to house it in a box and make extendiable buzzers later but its not working at all atm...

    any help would be appreciated
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    The fact that you have several duplicate circuits is a windfall to the debugging process. Hopefully you have access to a voltmeter.

    With a voltmeter you should be able to compare voltages at the same points in the circuit between one of the working stages and the stage that is not working.

    Is the board still not working at all?

    hgmjr
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    It may be tedious but I recommend you visually examine each of the components to:

    a.) make sure the component is the correct value and
    b.) in the case of the diodes, the leds and the transistors, it would be a good idea to look very carefully to make sure the component is installed in the correct orientation.
    and
    c.) check for cold or bad solder joints.

    The problem you had initially where a couple of the lights worked and a couple did not could be explained by a component installed incorrectly or a poor connection due to a cold solder joint.

    hgmjr
     
  4. gee_emm

    Active Member

    Jan 16, 2008
    34
    0
    I would double, and triple check the orientation of the the diodes and transistors to start,..to figure what went wrong,... and as hgmjr stated a voltmeter would definetely help.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hopefully, you placed the components on the side of the pc board so the leads came through on the side with the copper foil.

    We don't know what soldering iron you have, but wetting the tip with solder and wiping off oxide and excess solder before heating each joint really helps. A paper towel folded over 4 times and damp with water is a good tip wiper. Just leave it on the table top and wipe the soldering iron tip across it. Your solder joints should be nice and shiny, and the component leads should be visibly wet by the solder. Good old lead-tin solder is easiest to make good joints with.

    To check voltages, place the black meter lead (negative) on the negative terminal of the battery. All the voltages will be positive with respect to that point. Use DC VOLTS setting, and a range above 9 volts.

    Everyone on this board was in your situation at one time - if not many more!
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    The techs at my place of work have started using the spongeless solder tip cleaners. They say that their solder tips last longer since they are not frequently being baptized in a cool water sponge bath.

    I tried it myself and it seems to be very effective at removing excess solder.

    hgmjr
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    When you get 20 years on the same tip, sponges seem to do fine. I miss the sizzle with the brass curlies.
     
  8. rwmoekoe

    Active Member

    Mar 1, 2007
    172
    0
    "baptized" ? lol
    so we're all soldering iron priests, lol
     
  9. Stargate_to_Earth

    Thread Starter New Member

    Jan 24, 2008
    2
    0
    well i double checked everything when i put it in before i soldered it and i re-checked it... is it possiable that one of the componets could of went bad or something because its not working at all after it was partially working...

    as far as the volt meter i do have access to one but i am not quite shure where to check and how to interpert the results... you see i am an extreme novice to electrial circuits and i didnt completly understand them when i was in physics class my 10th grade year (i'm now a senior) so i dont know whats supposed to have current with no buttons pressed and whats not... (it's not as obvious as i had imagened)
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Electronic components are easily damaged by excessive heat. If you kept the iron on a joint for more than a few seconds, it's likely that you have "fried" some components.

    But, first things first. Test your 9v battery, is it still good? An effective test for such a battery is measuring it's current output through a 2.2K Ohm resistor. A fully charged battery will be able to create a current flow through such a resistor of just over 4 milliamperes; a fully discharged battery will have 3mA or less. Simply measuring the voltage across the battery without anything connected is not a valid test.

    With the battery out of the circuit, do a "bench check" on your semiconductors. If the meter you're using is digital, it may have a setting that looks like a diode; use that. If it's an old-fashioned volt-ohmmeter with a needle, use the 1K or 2K Ohm setting. Then start checking your diodes, beginning with D9. You should get a low reading in one direction, and a high (or open) reading in the other direction. Check them all, including the LEDs. Some of the LEDs may actually light up during testing, as many DVMs (digital voltmeters) output around 2.5v in diode test mode.

    Since this project is basically four copies of the same circuit, you can compare readings between the copies. If things are substantially different, you have found a problem area.

    Then, put the battery back in the holder, making sure it's properly installed (observe polarity). Turn on SW6. Set the meter to on 10vDC or 20vDC range. You should now measure 9V on one side of D9, and about 8.4V on the other side of it. If not, D9 is "blown."

    Then go to the junction of T1's collector and R3. You should measure roughly 7.8V to 7.2V there. If not, T1 is bad, R2 is open, SW5 or C1 is shorted.

    Press and hold the RESET switch (SW5). The voltage should drop to near zero, and then come back up when the reset switch is released. If it doesn't, check the voltage at the junction of C1 and R2; it should measure about 8.4V when the reset button is pushed, and around 7.5V when not pushed.

    Try that part and see if you find anything wrong so far.
     
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