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DC Motor Control Unit for Garage Doors

Discussion in 'Troubleshooting and Repair' started by TomJames999, Apr 11, 2015.

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  1. TomJames999

    TomJames999

    4
    0
    Dec 7, 2014
    Evening guys,

    I finally got my Voltage regulators from China which I thought to be the main issue unfortunately the motor control unit still doesn't work.

    Background: The remote switch have stopped working, change of the battery didn't help either so I've just just the Manual Switch on the box. Decided to add remote momentary push button which didn't work (possibly wrong connections and I might have Short circuited something) so I took it off and kept using the Manual Switch.

    After period of time the LED indicated (small red led at the left bottom corner) indicated that the circuit have power supplied however the button didn't work any more.

    I took my Multimeter to measure the following:
    • Voltage across DC Bridge: 26V
    • Voltage across Voltage Regulator: 30V
    Voltage regulator started to overheat really badly to a point where heat shrink burnt my finger. At this point I thought that Regulator is broken, but after replacing for a new one with higher amp rating (from 1A to 1.5A) the voltage is at desired 9V however the regulator gets hot really quickly.

    I took the PCB off and checked the switch, there is continuity across switch, the main Bulb, 5W resistor (which i placed under bulb), across Closed contacts of voltage relays which all works fine.

    Where should I be looking further for broken part?

    Circuit:
    [​IMG]

    Circuit explained to what I know:
    http://s17.postimg.org/qlg09wprj/20150411_183418.jpg

    Cheers,
    Tom

    edit: I just found something strange, the Big relay shows that Terminal 1 and 2 are NC, so I go a multimeter across them and they seems to be Open while Terminal 3 and 4 are NO but there is continuity across them.
     
    Last edited: Apr 11, 2015
  2. KTW

    KTW

    273
    15
    Feb 22, 2015
    Is the switch continuously closed causing the contacts to operate?
    That could be the reason it's overheating, is it fused?
     
  3. Tha fios agaibh

    Tha fios agaibh

    2,074
    685
    Aug 11, 2014
    Sounds like a shorted component somewhere, but without a print to look at its going to be very hard to find.
    You could start by checking the diodes and transistors for shorts. Remember to unsolder one side of diodes to isolate it from the rest of the circuit, before testing.
     
  4. Tha fios agaibh

    Tha fios agaibh

    2,074
    685
    Aug 11, 2014
    I see big relay nc contacts as
    1 and 5 and the other nc contacts as 2 and 6.
    If your getting continuity across 3 and 4, your likely reading through another component on the pcb.
    Usually, if relay contacts are stuck, they have obvious carbon marks where they got welded together.
    It does look a little dark in the corner of that picture.
     
  5. TomJames999

    TomJames999

    4
    0
    Dec 7, 2014
    The switch is closed almost all the time however the Line Regulator keeps on heating itself. I just realised that it actually might be mechanical fault on the switch.

    Resistance when Closed: 0.1Ω
    Resistance when Open: 875Ω

    Is that not a bit low resistance for an open condition?
     
  6. KTW

    KTW

    273
    15
    Feb 22, 2015
    0.1 will be a solid short.
    Can you test the switch out of circuit?
     
  7. TomJames999

    TomJames999

    4
    0
    Dec 7, 2014
    I made a mistake right there but I've unsoldered number of components and tried to follow the Schematics to see what's going on.

    Unsoldered the Push Button, works fine. The 5W resistor seems to be fine too, every other components doesn't seem to have any visible damage on them. What I found is that the Bulb is actually broken inside, that's why it didn't light up when I clicked on the push button.

    The Bulb itself is going to a Collector of HV Transistor MPS A42 and Collector of NPN Transistor Switching Transistor TIP 31C.

    Quick schematic (LS1 Broken Bulb):
    [​IMG]

    I will get a new bulb, but I still don't see how a single bulb could potentially affect the whole operation of the circuit. I'm guessing that live Open circuit is bad for Voltage regulator that's why it is heating so bad? We will see after I get new bulb.
     
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