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Beginner question: How do I let a 12v 36w current through only when a 1v signal comes from a source?

Discussion in 'General Electronics Discussion' started by Novogenia, Nov 26, 2015.

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  1. Novogenia

    Novogenia

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    Nov 26, 2015
    Hi everyone. Sorry for this extremely noob question, but im beginning to fiddle with electronic parts and Is am stuck.

    I have a broken 3d printer I am hoping to fix. Now the issue is this:

    I have a place on the motherboard that gives me a 1v current when the heating element should turn on. The power to the heating element is broken however and I would like to power this externally. The problem is when I just power it continously it gets too hot. So I would like to disrupt the power supply to the heating element if NO 1v signal comes from the motherboard.

    Any idea what components are right for my use? something very simple would be appreciated. ;)

    Thx a lot.
     
  2. Arouse1973

    Arouse1973 Adam

    5,164
    1,081
    Dec 18, 2013
    Hello, welcome to EP.
    First thing is why did the power supply fail in the first place. It is much better to try and repair the original circuit rather than feeding new power into a faulty PCB. Can we not help you try and fix the unit? Lets see some pictures of the faulty PCB first, nice clear close ups would be good.
    Adam
     
  3. Alec_t

    Alec_t

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    Jul 7, 2015
    Using the 1V signal to switch the heating element would be pretty straightforward, but as Adam said, it's best to find the cause of the problem first.
     
  4. Novogenia

    Novogenia

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    Nov 26, 2015
    Oh wow... trying to fix the PCB... While I thought I might have a chance to fix it externally (with some help) I thought a PCB would be unfixable... but ok... lets try that.. ;) Ill add some pics in a minute.
     
  5. Novogenia

    Novogenia

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    Nov 26, 2015
    OK, here it is... the two white cables are the culprits... I checked but no current there when there should be. Somewhere else I read that cleaning the heating element while on with a brush can create a short circuit somewhere on the board to blow a fuse or sthg. maybe thats it?
    Here a link to the images:
    https://www.dropbox.com/sh/zzsec51tnthxu8u/AABnU1I6hGWMUdaU-BBnc2uCa?dl=0

    thx a lot fro helping.
     
  6. Alec_t

    Alec_t

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    Jul 7, 2015
    Unfortunately, those pics are neither clear nor close-up enough to read component identifiers :(. Can you post better ones here, using the 'Upload a file' button? Can you post the schematic?
     
  7. Novogenia

    Novogenia

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    Nov 26, 2015
    Ok, here are some better ones. but thats the best I can do I think. I could also read everythingon the board. Let me know if this helps.

    I dont have a schematic as this is the interior of my 3d printer I commercially bought. sorry.

    Dont you think the 1v control of the 12V heating element would be easier to do?


    by the way: here is some text I got from another forum where I read about the possible issue that caused this. maybe this helps:

    "
    The problem is that the heater cartridge has exposed wires at it's body that the insulation does not cover. The brass brush being a solid short runs across these wires and if this happens while power is applied to the heater it blows the zero ohm resistors near the heater output on the board. They use these zero ohm resistors as fuses. Unfortunately unlike fuses they are not in any way, shape, or form easy to replace for the average hobbyist."

    does any one know where the zero ohm resistors are on this board?
     

    Attached Files:

  8. Arouse1973

    Arouse1973 Adam

    5,164
    1,081
    Dec 18, 2013
    Have a look at R272 it's located very close to the white wires, which I think is the heater output. Also have a good look for anything that looks like it got hot or has burn marks on it.
    Adam
     
  9. Novogenia

    Novogenia

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    Nov 26, 2015
    Ok, checked it. Well, im far from an expert, but R272 seems like an empty slot with 2 soldering spots and no technical element installed. I checked and found nothing that looked burned. ;/ Any other ideas?
     
  10. Alec_t

    Alec_t

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    Jul 7, 2015
    R22 and D4 might be worth checking.
    Zero-Ohm resistors are sometimes marked '0'.
     
  11. Novogenia

    Novogenia

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    Nov 26, 2015
    ok, with "checking" you mean to see if current flows across them.. right? Ok, i ordered a voltmeter and will check it then. What do I expect and what is a sign of it being the problem?`

    Also... noob question... what setting on the voltmeter do I need?
     
  12. Alec_t

    Alec_t

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    Jul 7, 2015
    I hope by 'voltmeter' you mean a DMM (digital multi-meter)? A DMM has Ohms ranges, current ranges and voltage ranges, and usually a diode test function. The latter would help to detect if D4 is open-circui or short-circuit and an Ohms range would enable R22 to be checked for open-circuit.
     
  13. Novogenia

    Novogenia

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    Nov 26, 2015
    Yes, I meant a digital Multimeter... sorry.. ;)

    I just received the model: DT830B

    Any recommendations what setting I need to use to measure the resistance of the PCB components? ALso what to expect when working and when broken?

    Thx a lot.[​IMG]
     
  14. huttojb

    huttojb

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    May 3, 2015
    Just a thought, if the board has conformal coating, which it should. Shine a black light across the pcb. This usually identifies any components that may of got hot.

    Jason.
     
    Martaine2005 likes this.
  15. Alec_t

    Alec_t

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    776
    Jul 7, 2015
    Set the Ohms range to include the expected value of a resistor under test. Measure with the probes first with one polarity then with the opposite polarity (in case there is a semiconductor junction, somewhere in the circuit, in parallel with the resistor). This test is not conclusive if there is any parallel current path.
    Use the diode test function for checking diodes and bipolar transistor junctions.
     
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