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Maybe the dumbest question on QRZ ever

Discussion in 'General Technical Questions and Answers' started by KC2KQH, Apr 17, 2004.

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  1. KC2KQH

    KC2KQH Ham Member QRZ Page

    I am still plugging away on the power supply, after a minor problem earlier (blew my meter's fuse, now back in business)
    Should these diodes be open or closed when the power is off.
    Ryan
     
  2. Guest

    Guest Guest

    If I read your question right, you are asking whether a diode should present an open or a closed circuit. The answer is both. The purpose of a diode is rectification. Thus, it will allow current to go one way but not the other. Thus it is a closed circuit in the forward direction, and open in the reverse direction.

    If that was your question there you go. But I am not sure that I read it correctly.
     
  3. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    RIQ "beat me to the punch"! A silicon (or germanium for that matter) diode will exhibit a relatively low resistance in the forward direction and a relatively high resistance in the reverse direction.

    For the 1N400X series this is usually around 500 to 700 ohms in the forward direction and more than 50K in the reverse direction. Now, many digital meters cannot accurately read diodes unless they just "happen" to have a "diode" position. If in doubt, use an old analog VOM!

    In a circuit, unless in parallel with something else (like an equalization resistor) you should get the forward and reverse readings when checked in the circuit. Occasionally, something in the circuit causes the reading not to be able to be used. But, in most cases, you can read these resistances.

    Now, if the diode is actually "shorted", it will read a very low resistance in both directions and definitely should be replaced. The same if it reads a high reading in both directions. Just to make sure that there is nothing else in the circuit if you just happen to get the same (or virtually the same) reading in both directions is to take one end of the diode loose from the other components and to measure the forward and reverse resistance.

    Especially if the diode (or diodes) is shorted, then you need to check the filter capacitors in the power supply as well as checking the circuits beyond the power supply for shorts or "near" shorts. Diodes very rarely "blow" without being affected from other components.

    Glen, K9STH
     
  4. KC9ECI

    KC9ECI Ham Member QRZ Page

    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (K6UEY @ April 16 2004,21:53)</td></tr><tr><td id="QUOTE">What ever happened to the old idea of opening the book and learning at least SOME of the BASIC Fundementals before asking questions whose answers are far above comprehension? [​IMG][/QUOTE]<span id='postcolor'>
    At least he asked a question. This time. With friendly folks like you, I can see why some people would choose ignorance over the risk of asking a question only to be publicly snapped at. Must be nice to know it all. I can only aspire to your example sir. I guess since anything worth knowing can be looked up in a book somewhere, QRZ might as well shut down the question and answer forum to spare you from such nonsense.
     
  5. K7FE

    K7FE QRZ Lifetime Member #1 Platinum Subscriber Life Member QRZ Page

    Diodes cannot be measured properly in the circuit.  You MUST remove one lead of each before testing, otherwise you will be measuring other components in your circuit in addition to the diode.  Transformers, resistors, pilot lamps, etc.  Some diode packaging contain more than one diode.  They could be configured with 2 or 4 diodes such as a &quot;bridge&quot; or a high voltage assembly with many diodes to accomplish the desired breakdown voltage.  Most commonly you will just find individual diodes in a package.
    73,
    Terry, K7FE
     
  6. Guest

    Guest Guest

    [​IMG]?

    WTF? It looks like he asked a question.
    Rather than jump all over him for having the fortitude to admit he doesn't know something, and ask someone, you should instead congratulate him.

    Jesus man, sometimes you just don't have the references you need in front of you. Sometimes you just don't know how to look it up properly. SOMETIMES you just want to get a second opinion.

    Small wonder more people make stupid mistakes, they're afraid of being jumped for asking questions! What happened to the old adage, 'The only stupid question is the one left unasked?'

    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Obviously I don't take the Liberal approach that new people are excused from learning and should be coddled and pampered,if you are going to sit at the big table with the adults then you should act like you deserve it.[/QUOTE]<span id='postcolor'>

    No, obviously you take the approach that everyone should have to make their own mistakes, and not TRY to glean knowledge from those who are more experienced than they. I think it was VERY adult of him to try to find out something, rather than screw it up by guesswork &amp; then whine about how 'It's too hard!'

    Lighten up.
     
  7. W0UZR

    W0UZR Ham Member QRZ Page

    Hi folks,,,

    Here is a CLASSIC example why I don't ask questions....

    I have dumber questions than this, but am I going to dare ask them?? Uh Uh.
     
  8. Guest

    Guest Guest

    Must be nice up on that cross.  Let me know how Barrabas is doing, ok?

    People like YOU are part of the reason we don't see many people with basic technical knowledge.  They're afriad to ask because people like YOU jump all over them because 'they should have known that.'

    Well guess what?  HE DIDN'T.  So what did he do?  HE ASKED HIS PEERS.  And one of his 'peers' jumped his case.

    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">what good is it to give him a technical explanation if he has not bothered to try to answer the question himself,I have raised my kids and have no intentions of raising some one elses[/QUOTE]<span id='postcolor'>

    How do you KNOW he hasn't bothered to try and answer it himself?  That's a mighty big ASSumption, and I'm curious how you came to it based on his post.

    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">What ever happened to the old idea of opening the book and learning at least SOME of the BASIC Fundementals before asking questions whose answers are far above comprehension[/QUOTE]<span id='postcolor'>

    Know what?  I did a little Googling on this subject, as I have none of my beginner's electrical books here with me, and NOTHING I saw explained this problem in the way he asked.  They were all WAY above and beyond that SIMPLE question of his.

    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">I don't condemn him for asking questions[/QUOTE]<span id='postcolor'>

    No??  I'd hate to see your idea of condemnation then, all you've DONE in this thread is condemn &amp; ridicule him for his question.  I'd imagine someone like you makes him REALLY proud to call himself an Amateur Op.  Way to go man, wanna make someone else feel like crap because they're not an electrical engineer?  Rather, wanna make someone else feel stupid because they have to begin somewhere?

    Oh, I forgot, up on that cross I guess you DO know it all, and that knowledge must be SUCH a burden for you.

    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">but he should not be so lazy as to refuse to learn the very basics[/QUOTE]<span id='postcolor'>

    Lazy to me would be scrapping the PS and buying a new one.  Seems to me that the whole purpose of his question was to LEARN the basics!  Maybe you squashed that desire out of him tho' and you won't have anyone bothering li'l ol' you any more!  

    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">I have raised my kids and have no intentions of raising some one elses.[/QUOTE]<span id='postcolor'>

    I just bet they're quite anxious to come to you with questions and to get you to help them learn new things.  You ever help them with homework, or did you just shout at them to open the book and figure it out themselves?  I can guess the answer to that one.

    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">This gentleman by his own admission did not know the purpose of a &quot;DIODE&quot;[/QUOTE]<span id='postcolor'>

    Another ASSumption.  He asked if they should read as open or closed 'When the power is off'.  That's a FAR cry from 'What is a diode and what does it do?'.

    It's SAD at how obviously anxious you are to try to prove your own superiority that you would jump on a beginner like this.  Let others SEE your superiority by answering questions and helping with a smile.  If you don't want to help, then shut the **** up and don't hit the post button.
     
  9. Guest

    Guest Guest

    UZR, feel free to PM me with anything you want to ask, if I don't know, I'LL post it and ask.

    I know there are at least a FEW people here who truly care about helping their fellow man.

    PM or E-Mail me, I'll not reveal who wants me to ask what. It's all from me as far as anyone's concerned.

    Really, I don't mind in the slightest.
     
  10. KL7FZ

    KL7FZ Ham Member QRZ Page

    I sure am glad the power was off. [​IMG]

    Makes you wonder how the meter's fuse got blown though, doesn't it?

    Sigh.....

    KL7FZ
     
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