Checking soldered boards (for shorts etc)

Discussion in 'Homework Help' started by KansaiRobot, Jun 2, 2015.

  1. KansaiRobot

    Thread Starter Active Member

    Jan 15, 2010
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    Hello everybody and thanks always for the help.

    I would appreciate your help in something very basic.

    Say I have finished soldering components to a perfboard according to some schematics.

    How do you pros check if the soldering parts have been done ok, check there are no short circuits , check that connected parts are effectively connected.

    I have been told that I can do it with a multimeter, checking resistances etc..

    Any help will be greatly appreciated
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,656
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    I check everything visually as I go then give it a once-over before applying power. The ICs are not put in their sockets until the power supply and ground connections are confirmed with a voltmeter.

    Rarely are the connections so complicated that they need to be verified with an ohmmeter.
     
  3. KansaiRobot

    Thread Starter Active Member

    Jan 15, 2010
    318
    5
    unfortunatelly i alreadydidthat and something is not working
    ive been told an ohmeter is of help
    please someone teach me the method
     
  4. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
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    Post your schematic
     
  5. KansaiRobot

    Thread Starter Active Member

    Jan 15, 2010
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    Here it is
    the A part and the B part are supposed to be isolated. however I suspect there is some interference cause one output supress the other.

    [​IMG]


    so how do I check for isolation with a multimeter??
     
  6. panic mode

    Senior Member

    Oct 10, 2011
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    which part A and part B? I see nothing with galvanic isolation in this circuit
     
  7. KansaiRobot

    Thread Starter Active Member

    Jan 15, 2010
    318
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    This is a SLA7026M. If you see the datasheet, inside that pink rectangle there are some FETs, op amps and stuff

    www.futurebots.com/7024.pdf


    In any case, my question is simpler than that.
    Say I have a circuit, any circuit. And I solder it on a perfboard. How do I check if the connections are ok or not?
    Say for example point P and point T should be connected, how do I check that with a multimeter. or how do I check there are no shorts in it. I have heard something about using the ohmeter or using the option with a small diode on it.
     
  8. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Not trying to be rude, but do you have the motor wire correctly to the driver board? In your other thread the motor it's self was never addressed as to type or model. Since your using a unipolar motor it should have either 6 or 8 leads. If it has, are they wired correctly?
     
  9. Technetium

    New Member

    May 26, 2015
    4
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    In any case, my question is simpler than that.
    Say I have a circuit, any circuit. And I solder it on a perfboard. How do I check if the connections are ok or not?
    Say for example point P and point T should be connected, how do I check that with a multimeter. or how do I check there are no shorts in it. I have heard something about using the ohmeter or using the option with a small diode on it.[/QUOTE]


    With the Ohmmeer you can find if there is a short or open where there isn't soppose to be by placing the leads on point P and T, if it reads 0 Ohms the there is a short, if it reads "open load" or "OL" then it is well, open.
     
    KansaiRobot likes this.
  10. KansaiRobot

    Thread Starter Active Member

    Jan 15, 2010
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    It is a custom modified motor as far as I know (meaning not in the market), but I got the data sheet and I am taking care of wiring the 6 leads to the appropriate place. Its voltage rating is 5.95V current 0.7A 4 phase 1-2 phase ecitation 1.8deg at full step. DC resistance 8.5 Ω to be driven at DC 24V.
     
  11. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    So have you scoped your outputs with no motor? A custom modified motor? Modified by whom? Opening up stepper motors is normally seen as a 'no-no', due to the close clearances internally and the magnetic strength involved in one. So I would be suspect of a 'custom modified' stepper motor, since it can possibly effect the drive also. Unless the modifications are done in the original motor factory.

    Have you tried a "standard" unipolar motor on the circuit? Have you tried the 'custom' motor with a off the shelf driver? (Off the shelf is way cheaper than a do it yourself) When/if the drive circuit is a 'proven' item and the motor is 'custom', where would you think to look first?
     
  12. KansaiRobot

    Thread Starter Active Member

    Jan 15, 2010
    318
    5
    Excuse my english. Perhaps I didnt use the right term. What I meant is that the motor maker released a model only for us. Please, dont ask me the politics of this or the reason since I dont know any of them. I have just given the motor and tasked with building a driver to control it

    On other thing, you said "have you scooped the output with no motor?". I was told something similar once, but how do you do that??
    I mean, yeah I can put the terminals of the oscilloscope in the outputs but then I realize the motors are an integral part of the circuit that connects the output terminals to the 24V power. So if I eliminate the motors all I got is an open circuit, dont I??Therefore the readings there would be quite different with the real ones with the motors...

    I can be totally wrong (I frequently am!) so Please explain me how so and how I can do what you said, ergo scooping the outputs with no motor
     
    Last edited: Jun 4, 2015
  13. panic mode

    Senior Member

    Oct 10, 2011
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    if you build circuit, normally visual inspection and some probing of circuit would be proper before powering up. before we use multimeter, we need to have some idea what readings we should expect. for example, in your circuit, before powering up you can:
    - check resistance of motor windings (to ensure connections are not mixed up; measuring across OutA and Out-A should be double value of measurements from Vcc to either OutA or Out-A). according to your info max resistance is 8.5ohm so if yo read anything higher than that, you have a problem.
    - check that there is no short circuit between power rails (24V, 5V and GND). reading low ohms would mean a problem. if you look at block diagram, there are diodes across each output channel so if your red multimeter probe is on GND and black on Vcc, those diodes will be forward biased and you will get lower reading than when probes are swapped.
    - if you check resistance between 5V rail and TdA or TdB, readings exceeding 47k mean you have a problem (they can be lower due presence of other components, providing various paths for leakage current).
    - your circuit does not use current sense resistor so if there is an overcurrent situation, something will smoke (so this must be calculated risk).

    Once circuit is powered, check if voltage rails are really what they are supposed to be. if not, there may be significant current draw. your stepper motor should work even if supply voltage for motor is lower than 24V (you may probably test it at 5V first). higher supply voltage allows faster rise time (acceleration). If you have an oscilloscope, you can monitor levels and wave forms on inputs and outputs and compare with logic tables etc.
     
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