Help me get a job

Discussion in 'General Electronics Chat' started by jmoffat, Feb 14, 2014.

  1. jmoffat

    Thread Starter Member

    Jul 18, 2012
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    Hi everybody. I recently responded to a advert for an electronic equipment technician. This company refurbishes equipment used in semiconductor manufacturing. Two of the stated requirements for the job are a knowledge of transistor biasing and knowledge of variable frequency drives. I am good with bipolar transistors, a little weak with fets and really need help with mosfets. Can anyone direct me to a website or other material that will help me get up to speed quickly. If I get past the phone interview Monday they will invite me to interview with them in person and take a written examination. Also I need to learn about variable speed drives. In the past I have always treated them as black boxes. They either work or don't work. I assume they repair defective boxes. My guess is that the most common failure on a variable drive is the mosfets.

    This question just occured to me, Why are triacs not used in this application? Or are they?
     
  2. #12

    Expert

    Nov 30, 2010
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    Triacs have a voltage cost of 2 junctions while current is flowing. Mosfets can be had with milliohm ranges of resistance.

    Do the math. 40 amps through a 1.4 volt triac wastes 56 watts.
    40 amps through 8 milliohms wastes 12.8 watts.
    If you parallel 2 triacs, you still waste 56 watts.
    If you parallel 2 mosfets, you waste 6.4 watts.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    IGBT's are also common on VFD's, with Triacs it would be hard to duplicate the PWM control of a variable frequency pseudo sine wave.
    Max.
     
  4. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Why would you want a job?

    I have had several and not one ever lived up to the hype or promises made during the interviews.

    Take a few steps back sit on the couch for a few days and play Xbox. The feeling of wanting a job will eventually pass just like a bout of food poisoning does.
    If not there are medications that will help. ;)
     
  5. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,809
    834
    What have you been on? Being unemployed, I am baffled by this post. 'Nuff said.
     
  6. takao21203

    Distinguished Member

    Apr 28, 2012
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    No he's right. Confront the HR team friendly but with determination.

    Say what you want to do.

    Why you want to do this job.
    Why you want to work this company + location.

    Make demands and be honest and be yourself.

    Don't lie and candify yourself.

    A VFD? Well that's a kind of a motor controll circuit. If it go nuts you need to know where to get a new one or an exact replacement.

    dude. These days, no one is fixing PCBs.
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    And they are legal in several states now......;)
     
  8. takao21203

    Distinguished Member

    Apr 28, 2012
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    come on keep it real the med's have not yet been specified.

    If OP never worked on a VFD and its a direct requirement, well I'd ditch it, just.

    You don't just need to know the theory also how they look like, where you can get them, pretty much all about it.

    These jobs are highly specialized and chances breaking into it are dim.

    It's like 400 volts gear, you can read 20 books about all the aspects but if you never worked with it directly and they put it as requirement, you need good arguments and there will be others who actually worked with the stuff and know all the aspects of it.

    On the other hand it is not that difficult to get along with that technology.
     
  9. rc3po

    Member

    Feb 12, 2014
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    Why not repair PCB's? Most of the time the problem is e-caps, cold solder joints, or a broken track - what's the big deal? Personally, I love fixing stuff. I love studying PCB's and trying to fix them. Of course, if I was a rich spoiled brat, I might just throw them away. I don't know...
     
  10. takao21203

    Distinguished Member

    Apr 28, 2012
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    A PLC technician is not supposed to know too much about how the PLC is composed or how it actually works.

    If there is a failure, the whole PLC module is replaced.

    Sure there are still a lot of facilities with antiquated equipment- pretty much everything from relays to TTL circuits and single board computers.

    you would not have much of a chance to repair a PCB for a modern single board computer.

    Also, if these PCBs do have a fault, other parts on the PCB also are just on the margin of malfunctioning too. Fix one bug, a few weeks later, spurious errors and soon the next failure.

    So instead of fault finding and repairs 5 times, also replace the whole thing.

    There can be the case where you really have a rack with thick wires and some relays and you know exactly how it works without schematic, and then you replace a single component. I don't deny that.

    There is also the case of 10000s or more than that fridges which are still perfectly funtioning but worn down + discarded. Same for countless other household appliances. Or somehow they end up being used in Africa and nobody knows.
     
  11. rc3po

    Member

    Feb 12, 2014
    56
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    Yes, with computers and modules etc.. that you mention, I agree. I was thinking more on the line of TV's, and simpler devices. There is a time & place for everything I suppose. Thanks, I'm really learning a lot from you guys. This is a great website!
     
  12. #12

    Expert

    Nov 30, 2010
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    Example: Warranty service house call. It's a bad DVD drive in a new computer. The DVD drive costs Dell or ASUS $38. How many hours can you spend playing, "name that transistor" before you cost your employer $38?
     
  13. takao21203

    Distinguished Member

    Apr 28, 2012
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    It is usual business practice AFAIK to refurbish semiconductor equipment and then sell it for secondary use.

    This is complex equipment with some of it's technology demanding very tight mechanical tolerances.

    Of course it wears out gradually over time, and maybe only some of it can be fixed reasonably.

    So a estimate is made. What kind of manufacturing proccess is it still good for, and for how long iit can be used.

    Maybe the alignment is not so good anymore so it can not be used for the maximum level of fine structures it was originally used for.

    The work would include all kinds of measurements, replacements, patching, repairs, testing, handling of chemicals and mechanical cleaning.

    If OP has a knack for that kind of work and these kind of machines, it does not really matter if he actually does know all details about VFD.

    On the other hand if not, you would make problems with that machine only worse.

    Like a DVD rewriter which had a supposed to be misaligned metal disc glued to the metal encasing but after removing it, it no longer writes DVDs.
     
  14. rc3po

    Member

    Feb 12, 2014
    56
    1
    Lol! Very true, sir. But I have a 1 year old Sanyo LED/LCD and if it messes up, I'll pull the back off and find out why. But I'm disabled and have the time I guess. You are right, it depends on the Device & circumstances.
     
  15. #12

    Expert

    Nov 30, 2010
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    I'm glad you understand.
     
  16. inwo

    Well-Known Member

    Nov 7, 2013
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    I do very well repairing things that are not worth repairing.
    Battery chargers, welders, fencers, strobe lights.

    Not much per hour but working from home with no overhead helps.

    And being my hobby, if I wasn't getting paid for fixing something, I'd be spending money for hobby parts.:D

    I have a bunch of PLCs that fail every 10 million relay cycles. Even when driving high impedance loads. Just wear out mechanically.

    I've done so many, it's a 15 minute job in the field, and saves the time rewiring and reprogramming.

    I know there are permanent fixes, but that takes time and money too.
     
  17. rc3po

    Member

    Feb 12, 2014
    56
    1
    I'm the same way; I love fixing stuff. Every time my great nieces toys quit, they bring them to me to fix. Yeah, fixing a $20 doggie isn't anything to brag about, but the smiles on the babies faces when their toy is working is priceless!
    I even fix wall warts. Why buy a new one if I can repair it in 30 minutes?
     
  18. #12

    Expert

    Nov 30, 2010
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    Your nuts.

    Welcome to the club. :D
     
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