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Laser printer - Drum positive or negative?

Discussion in 'A+' started by ledzepploid, Feb 10, 2009.

  1. ledzepploid

    ledzepploid Bit Poster

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    Hi,

    Just a quick question about initially charging the drum.

    I was under the impression it was a negative charge of -600v (as I learnt in my studies), however I am using a practise test program and it says I got that wrong, it says:

    Q) "Which of the following describes how the drum in a laser printer is initially charged?"

    A) "The charge corona wire imparts a positive charge on the drum"

    So I checked the net and discovered this source agrees with the answer.

    But then I discovered this pdf which agreed with what I had learnt.

    Which one is it? Or are they both right but one applies to older laser printers?

    Cheers
     
  2. Tinus1959

    Tinus1959 Gigabyte Poster

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    Ok. The drum is grounded, but the coating is not. If there is a charge on the coating, the erasure lamp will discharge the charged coating to the ground level of the drum. The erasure lamp clears a previous image on the drum.
    Than you have the primairy corona, which charges the photosensitive particles on the surface of the drum. This charge is negative and between 600 and 1000 volts.
    The laser 'writes' the image to the drum by discharging the particles partly (about -100 volts).
    The toner, which has a charge of some -300 volts (by the tonor cylinder), is attracted bij the -100 volts of the written image. In comparison with the toner, the image is less negative (what could be translated to positive).
    Than you get the transfer corona, with a positive charge, which will give the paper a positive charge and therefor attracting the paper to the drum and tranfering the toner to the paper.
    Next the charge is removed from the paper by the static charge eliminator.

    Source: Mike Meyers all in one, 6th edition. This book is considered to be the best in the field.
     
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  3. Bluerinse
    Honorary Member

    Bluerinse Exabyte Poster

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    The older selenium drums held a *positive charge*, they have mostly been replaced with OPC (organic photo conducter) drums over recent years. from my experiance OPC is *negatively charged* by the charge corona.

    So, as with so many things, it depends.

    Edit.. found a linky..

    http://en.wikipedia.org/wiki/Xerography
     
    Certifications: C&G Electronics - MCSA (W2K) MCSE (W2K)
  4. ledzepploid

    ledzepploid Bit Poster

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    Cheers for the replies.

    I'm currently doing a sybex test. I choose -600v and it claimed it was +600v. The question has no mention of which type of drum is in use.

    If it comes up in the real exam, should I assume its the old type of drum unless otherwise stated? Otherwise theres only a 50/50 chance of getting it correct if the type of drum is not specified.
     
  5. Bluerinse
    Honorary Member

    Bluerinse Exabyte Poster

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    Sorry, but it's Impossibe to answer your question. Why not take it up with CompTIA?
     
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  6. ledzepploid

    ledzepploid Bit Poster

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    Head to comptia.org and stick that question in the contact us form? I really cant see them responding.
    I asked it here because many here have already taken the exams, and perhaps that question has come up.
     
  7. Bluerinse
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    Bluerinse Exabyte Poster

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    Maybe it has, but how would anyone know they got it right?
     
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  8. ledzepploid

    ledzepploid Bit Poster

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    ok fair enough, hopefully comptia wont be as flawed as practise exam software.
     
  9. r.h.lee

    r.h.lee Gigabyte Poster

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    ledzepploid,

    What make and model is the laser printer?

    The problem with both of your sources you've cited is that NEITHER of them are printer manufacturer documents but instead are basically opinions, even the one in PDF format.

    The document "Laser Printing Process" by VN Publishing comes with the following notice...
    [quote="Laser Printing Process" Publication from VN Publishing]
    Notice: Every precaution has been taken in the preparation of this material to ensure that only the most oaccurate information is being provided. Neither the author nor VN Publishing assumes any liability in the event of loss or damage directly or indirectly caused by inacuracies or incompleteness. This information is provided "As-Is" with no warranty expressed or implied.
    [/quote]

    Basically the legalese of the above-mentioned bolded text states that "...this is officially only an opinion and since we won't stick our legal necks out to certify this information is factual enough to be relied on, you shouldn't legally rely on this publication either."

    The webpage titled "How Laser Printer and Printer's Components Work" by Nachiketa Mishra states...
    [quote="How Laser Printer and Printer's Components Work" by Nachiketa Mishra]
    Learn more about available Printer and Printers Accessories at Superwarehouse.com Apart from Xante Printer and Printers you will find numerous other brands of hardware and software components here.
    [/quote]

    To me, this article screams "seems educational but in fact it's an online infomercial for the website Superwarehouse.com." Also, if you look at the author's information it states...
    Apparently, "SEO' stands for "Search Engine Optimization" according to the title of an article by a David H. Hobson. So Nachiketa Mishra's article wasn't so much designed to be factual but designed to pop up near the top of your search engine search. Technically, if you too posted a post here on CF stating "laser printer drums are initially -600v" then you too can be "experienced" in "content writing."

    Source:
    1. Nachiketa Mishra - EzineArticles.com Expert Author - http://ezinearticles.com/?expert=Nachiketa_Mishra
    2. "Search Engine Optimization Services" article by David H. Hobson - http://ezinearticles.com/?Search-Engine-Optimization-Services&id=1986606

    So in summary, the answer to your question is highly dependent on the make and model of laser printer that you're dealing with and which convention it uses. Did my post help?
     
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  10. BosonMichael
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    If we've gotten that question, we're not at liberty to discuss it, because we signed a non-disclosure agreement (NDA) when we sat down to take the exam... and those carry quite a bit of weight. Failure to abide by the terms of the NDA can cause CompTIA to revoke your certifications and ban you from any future certifications for a period of time (up to a lifetime ban). Not worth it, dude.

    You're right, CompTIA's probably not going to respond. If they did, over time, they'd reveal their entire question pool. So that's not going to happen. If you get a question like that, just give it your best guess and move on to the next. I doubt one question's gonna be your downfall... it'll be all the other ones you get right or wrong that'll make the difference.
     
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  11. BosonMichael
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    Unfortunately, they're as bad or worse. CompTIA is notorious for badly worded questions with multiple right answers (or no right answers at all). This happens because CompTIA lets just about anyone who has passed a previous version of their exams to write test questions for future exams... and the people who edit the questions just don't know any better. If they did, those questions wouldn't appear on their exams.

    That said, a few bad questions isn't likely to be your downfall. You should know your material well enough so you can tolerate a few of these bad apples.
     
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  12. ledzepploid

    ledzepploid Bit Poster

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    Yep very detailed, cheers for that fella.

    Doh not what I wanted to hear! I also didn't realise there was a NDA. Thanks for the info Micheal.
     
  13. soundian

    soundian Gigabyte Poster

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    Looking in the Sybex book they state a multitude of times that the drum gets a -600V charge so it sounds like a glitch in the test to me.
     
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  14. BosonMichael
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    Glad to be of assistance. Still, don't stress out about it... the test doesn't require you to get a perfect score... it's designed to see if you can get a passing score, which is *absolutely* possible despite the poorly worded questions.
     
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  15. ledzepploid

    ledzepploid Bit Poster

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    You were not wrong about the question wording, some of it was awful. In the end this charging question never come up anyway. It actually seemed a bit easier than the sybex test.

    Now its 602 8), shall be giving myself a little longer than a week to revise this time, wasn't a fun week!
     
  16. BosonMichael
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    I'm not surprised - I've seen (way) more than one CompTIA exam, and they ALL seem to be like that.

    Congrats!
     
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