does this schematic look right to you ?

Discussion in 'General Electronics Chat' started by reapairman, Apr 5, 2013.

  1. reapairman

    Thread Starter New Member

    Dec 27, 2011
    17
    1
    i've drawn part of my fan controller that I'm reverse engineering.

    I'm new to eagle so it's a bit messy and incomplete but the main part I am trying to figure out is the top right circuit that provides power to 7 ic's - phillips CMOS hef 14 pin schmitts and nands invertors etc. 2 IR2106s mosfet drivers and 2 unknown ic's so far.

    [​IMG]

    If it's a commonly used power supply could someone tell me what kind it is ?

    also one of the components I've listed as ZD10 - not sure if it is actally a zener. the 2 red bands are closest to the gate of the mosfet.

    it's got red,red,black,silver bands on it and can be seen in the pic below, just below the 1002 resistor.

    [​IMG]

    Also, the motor states 24VDC nominal and it looks like the B+ for the mosfets -> coils is much higher than that. anybody know why ?

    I've attached the eagle schematic too.

    many thanks
     
  2. #12

    Expert

    Nov 30, 2010
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    It seems pretty odd to me that the main supply voltage is 335V DC.
    Are you seeing capacitors (C5) that are labeled for more than 335 volts?
    Still, the IRF830 can handle that, if that isn't the part that exploded.
    The red, red thing is inconsequential at this point, it is 22 ohms, 5%.
    ZD9 is of interest as to its value. See if you can get a voltage measurement on that.
    You're going to be measuring voltages, really high voltages that can kill you.
    Are you prepared for that?
     
  3. reapairman

    Thread Starter New Member

    Dec 27, 2011
    17
    1
    thanks for your reply #12, yes the capacitor on the B+ rail (c5) is rated at 400v 200uf - from memory.

    ah so ZD10 is actually a resistor - thanks.

    I will update the schematic.

    high voltage is ok, as long you respect it and dont give it tongue on the first date. ;)

    I'm used to working on valve amps, so try to tread carefully with electricity.

    saying that, I 've still shocked myself many a time, although usually not through my heart (hand to hand), just finger to floor, through thick shoes and a mat underfoot.

    had a few scary 600 volt jolts from filter caps, loads of 240v tingles and nasty nips from 50v DC when sweaty. but am generally careful after my first big shock when I was a teenager. it was summer, so I was wearing shorts and building a variable voltage rectified power supply on a wooden board on my bare legs, late at night, a wire slipped onto my leg and I got fried for a second or 2 (guess we didn't have any RCD back then). put my hair up on end, burnt my leg, had me yelling/screaming and I was in shock, brain in hyperdrive which made me temporarily afraid of the dark, the noise woke up the whole house and my dad gave me a massive row for making a such a racket late at night. wasn't a pleasant experience so I do my best to avoid get shocked.

    2 of the mosfets had shorted, taking out the fuseable 10ohm resistor R50 I was thinking of removing the other 2 motor mosfets and then powering up the circuit to measure the voltages to the rest of the circuit, but not sure if the mosfet hi/lo drivers will be damaged if the mosfets are not there.
     
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  4. #12

    Expert

    Nov 30, 2010
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    I click you one, "Thanks" for the LOL.
    and now I know how a beginner on this site makes such good drawings.
    I'd tell you about the 450 volts I got across the heart at 18 years old, but that, also, is not first date material. The only thing that matters is that it made me so careful that I survived another 40+ years.

    So...where are we...unsolder (disconnect) the FETs. Yes. Those drivers can wag the empty socket all day and not get frustrated.

    ps, I don't do .sch files. Try to get your postits up in .png.
    pss, I'd really like to get some voltage measurements on that upper right voltage regulator. I can see how it works, but some specifics would sharpen the focus for me.
    psss, good of you to tell your background experience or the moderators might have gotten hinky about safety issues. Power supplys straight off the mains is forbidden here.
    pssss, please click on "User CP" and enter your location. It helps us imagine what your residential power lines are and where to get parts.
     
    Last edited: Apr 6, 2013
    reapairman likes this.
  5. timescope

    Member

    Dec 14, 2011
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    44
    I have redrawn the circuit with the zener diode replaced with 22Ω.

    Timescope
     
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  6. reapairman

    Thread Starter New Member

    Dec 27, 2011
    17
    1
    cheers for the replies guys

    #12 - you'll need to tell us that story at some point, you've got my interest now. 450v across the heart would give anyone severe fear!

    thanks for the compliment on my schematic, I'm usually a messy bugger but I am working on it. I'll add my location (bristol uk - got some family living near you in Largo tho) and background to my profile, good idea. I've done a little of the circuit in LTSpice as well as eagle, but might try it in other simulators/editors just to familiarise myself with them - what do you use yourself ?

    knackered myself out yesterday mountain biking so not had much time to work on the circuit the last few days and off to the garage now to finish fixing my mig welder so I can get round to repairing/building stuff. Will probably do some more tracing tonight and then post an update. might even get round to powering it up and then measuring some voltages.

    timescope - many thanks for updating/editing the schematic, it looks a lot more legible that way, I'm used to drawing valve circuits but not got the hang of transistor layouts yet. It looks like the transistor on the left regulates the circuit by shorting out
    r13 (10k) but I'll need to simulate this to understand exactly what's going on.
     
  7. timescope

    Member

    Dec 14, 2011
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    At a certain voltage at B2, ZD1 conducts switching on the transistor on the left and this turns the mosfet transistor off by short circuiting the gate and source.

    This means that the mosfet is only on when the rectified sine wave voltage is low at the beginning and end of the half cycle and a capacitor maintains the output voltage when the mosfet is off.

    Timescope
     
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  8. #12

    Expert

    Nov 30, 2010
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    I don't simulate. Those programs frustrate the $%^& out of me. I'm an old analog guy who can hold a circuit in my head long enough to understand it.

    As for the 450 volts: Eico Signal Tracer kit. I built it. Toward the end, I plugged a probe into a random jack to make it hold still while I soldered. Got done, turned it on, and unplugged the probe.

    The plug on the probe had a screw head showing, uninsulated. I had plugged it into a 450 volt DC supply intended for vacuum tubes. Left hand to right hand with 450 volts, unregulated and unlimited except by the impedance of the transformer.

    The next time I got a thrill was when a horizontal output tube with a cracked anode cap stitched my hand with little black holes at 15,750 Hz.

    By the time 440V 3 phase vaporized the end of my screwdriver, I had my safety procedures down so well that me and 3 other guys just blinked at each other until we understood that nobody got a jolt.

    (Defective 3 phase disconnect switch only disconnected 2 of the phases.)
     
    Last edited: Apr 8, 2013
  9. reapairman

    Thread Starter New Member

    Dec 27, 2011
    17
    1
    cheers timescope, that makes a lot of sense. need to brush up on zener PS theory.

    Been crawling under my car last 2 days, pinhole leak in my power steering lines. still not finished it yet, hopefully tomorrow. can't decide if I prefer electronics or mechanics, they are both dirty, frustrating but satisfying once fixed. then I can finally get on to the pcb live testing.

    ordered another replica fan off ebay for cheap, with the same fault, I'm hoping to be able to read the last 2 ic codes that are unreadable on mine, then I can finish the schematic properly.

    #12 - ouch ouch and ouch! - it's all good fun, until fibrillation takes over.

    your right tho, the brains the best simulator, if you can hold the circuit in your head, that's quite a skill. I wish I could, but my memory is too fragmented. can sometimes visualise it in my sleep and wake up knowing (or imagining) how it works.
     
  10. #12

    Expert

    Nov 30, 2010
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    The moral of the story? NEVER TRUST ANYTHING. Not even a 2 foot square, 3 phase disconnect box, that looks perfectly normal and fairly new.

    The soft way I say that is: If you keep accepting a percentage chance of getting hit, the percentages will eventually pay off.

    Problem is, death is lurking where you don't think you are accepting a risk. My solution is what I call, "Layered Safetys". I turned off the 3 phase disconnect, and I moved a rubber mat so I could stand on it, and that was on top of a wooden grate on top of a tar coated flat roof, and I used an insulated screwdriver, and I had insulating shoes on, and I had one hand in my back pocket, and I had 3 men there in case I needed to be rescued, and I did NOT measure the voltages after I shut off the disconnect. I didn't believe I was accepting a risk, but I was wrong.

    The long term effect of this is that I actually break out in a sweat if I only have 2 layers of safety in place. Any one layer can be eliminated by a simple slip of the hand. The second layer can be faulty because I didn't think it out properly. If I have 3 layers I stop actually sweating. On that 440, 3 phase job, I had 8 layers in place. That is why I am still alive.

    Rules for the safety man: Do not talk to me, absolutely do not touch me, and do not stand within 6 feet of me. He needs to be far enough away to be clear of the initial blast or electric current if something goes wrong. That way, he will still be able to make choices about how to clear the fault.

    Remember this when you plug in to 220 volts and try to measure the circuit voltages.
     
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