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Circuit Card - Black Marks ?

Discussion in 'Troubleshooting and Repair' started by CanYouHelp, Oct 19, 2018.

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  1. CanYouHelp


    Oct 19, 2018

    I was wondering if someone would be able to help me ?

    I have attached a picture of a circuit card from a domestic fan. The fan has stopped working.

    With reference to the attached picture I note some discoloration down the left hand side together with blacked areas around what I believe to be capacitors ?

    Does this discoloration and the black marks indicate what the problem could be ?

    Many thanks in advance.

    Attached Files:

  2. dave9


    Mar 5, 2017
    This circuit does not look like it's crucial for the basic operation of spinning a fan. More information about fan make/model/device might help. I looked up "Vent-Axia" and they appear to make HVAC systems which would be consistent with my suspicions below.

    It looks more like a control board that takes AC input, provides a crude power supply for a logic circuit, and a remote relay for turning the fan on and off.

    How old is this equipment? Darkened areas could just be the long term effects of components that generated heat for years, or could suggest an area to investigate component function further.

    If I'm correct that this is just a fan controller board then the first thing I would do is use a multimeter to check for power input to the board with a multimeter. This of course requires working the mains voltage so some caution is necessary.

    If power is making it to the board then I would determine which wire to the fan is always continuous and which is switched by what I assume is a big blue relay. I would measure whether power is getting to the relay pin, and I would look at the specs on the side of the relay or pull up its datasheet to see what the relay coil activation voltage is and apply that voltage to see if the relay clicks on. You do not need this circuit powered with mains AC to do this relay test, I mean you can use an alternate power supply, say a random 12VDC plug pack adapter for power if it falls within the specs, or a bench power supply, etc (you did not mention your level of equipment and skills yet).

    If the relay works in this test then you can measure for continuity between the always powered relay pin and the output to the fan. If you have no continuity when it is switched (clicks) on then the relay is probably bad. If you do have continuity then it is time to put the circuit back in place and try to get it to activate.

    Trying to activate you would measure on the relay coil pins to see if they're getting the power needed to activate the relay. If there is no power to the pins then you would trace back that circuit to see where the signal stops and if there is remote sensing that locks out the circuit you may need to check the sensors involved in doing that.

    Having written this much, I might have gone off on a tangent and will wait for more info from you.
    Last edited: Oct 20, 2018
  3. davenn

    davenn Moderator

    Sep 5, 2009
    doesn't appear to be in this case … looks more like glue for holding components

    see my comment above

    a better photo, closer up, well lit would confirm what I have said

    73's de Edd likes this.
  4. dave9


    Mar 5, 2017
    Yes dark could be glue around the capacitors but I think I also see some darkening around the diode in the middle next to the blue (relay?) and around the transistor (or triac, or maybe a diode just to the southeast corner of it) up near the top left of the board.

    None of that looks indicative of certain failure to me so I'd trace the circuit at the point of the relay forward and backward, but also look at the PCB traces where the darkened areas are to see if the pads or traces lifted up or there are solder joint failures from the heat.
    Last edited: Oct 20, 2018
  5. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir CanYouHelp . . . . .

    I can help . . . . . .

    Comment 1 . . . . yeth! . . . . the dark brown pookie is just being captive adhesive for those E-caps.

    Question 1 . . . . . has the plastic at the pins 7- 8 end of the Tejas Iinstrumentations CD4051's case, blown up and fractured off . . . .or is that being just a perceived optical collusion ?

    Would also like to know what voltage is coming in on the RED and WHITE wires connectors.
    If AC, I would guesstimate the LARGE MAIN power supply E-cap to have the four discrete diodes to it's 7 o'clock position, as being its FWB rectifier supply and the slightly smaller E-cap to its left . . .being a second in line filter cap.
    Then just up above it would be a 1 watt ZENER regulator diode that has been working hard over time and discolored the PCB around its leads.
    The closest TO-92 transistor to the main filter cap would be the relay driver transistor with its suppressive flyback diode being nearby.
    Up above the secondary E-filter cap could be a TO-92 cased low power regulator . . . viz . . .78L05 for the logic supply voltage, and having its associated E-filter cap located just above it.

    73's de Edd
    Last edited: Oct 20, 2018
    Richard9025 and HellasTechn like this.
  6. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir CanYouHelp . . . . .

    Gravitated afterthoughts . . . .

    With a limited view of ALL of the component side of the PCB, I believe that they are just using an " economy" technique on the power supply design for this board.
    With more credence given to the RED and BLACK wires and connectors as being the switched output contacts of the power relay.

    Specifically . . . . . I think that at the bottom left quadrant of the board that I see just the slightest minute glimpse of the edge of a BLUE cased varistor that is being across the AC line input to clip and suppress any sporadic high line voltage spikes.
    That is being, to further protect the HOT side of the AC line, which is then being connected to the right terminal of the large YELLOW poly cap . . aka . .426124C with its AC input on its right side and AC output out its left side which then passes up and into and out of a 22 ohm 2W metal film surge / trimming resistor.

    That hot AC then goes into a + - pair of the set of 4 full wave diodes, that uses the reduced AC voltage, created by the resistor PLUS the AC capacitance reactance of the poly cap, to feed the units low voltage supply.

    Reading the MAX voltage rating of the MAIN capacitor should suggest the somewhat reduced voltage of the highest supply that feeds the power relay.
    As well, the reduced 2 lower voltage ratings of the 2 other E caps, should estimate the voltages associated with the sub supplies.

    You can see that top center TO-92 cased device has been assigned a Q 1. . . . .transistor . . .symbol identifier.

    As well, the far right DIP packaged IC, has been assigned U3, with its companion to the left being U2.
    Therefore, a like possibility, is for the suspicioned TO-92 just to its left, to be a U1 assigned 78L05 regulator IC.

    That leaves relay driver transistor to be Q2.

    At the top left corner I see a 3 conductor ribbed . . . . .WHITE- - - -WHITE RED BAR - - - - WHITE RED X . . .. that could relate to an adjustable pot connection, thermostat. or its outputting to LED's for run /state conditions ? ? ? as is to be confirmed.

    Any further assistance on my part would be dependent upon a, squared within the frame , straight on, full frame, well lit, in focus, photo of the component side of the board with ALL of its components.

    ALSO, a like photo of the OTHER foil pattern side of the board, so that I can " read " it.

    BTW is this being an intermittent use type of ventilating fan, as might be used in the ceiling of a bathroom ?

    73's de Edd
    Richard9025 likes this.
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