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Clicking/Buzzing relays

Discussion in 'Power Electronics' started by timtam75, Aug 18, 2019.

  1. timtam75

    timtam75

    5
    0
    Aug 18, 2019
    Hi this PCB is for a stove/oven range hood. These white relays were clicking rapidly/buzzing. (Fan and lights that it controls are still working fine).

    It seemed to be coming from two relays and you could actually see a spark flickering in one (probably from the rapid switching). I replaced with new ones but still making the same noise.

    I have limited knowledge, but have a multimeter I can use in basic modes.

    Can anyone give me an idea of what to check next? Youtube Link below.
    Thanks
     
    Last edited: Aug 18, 2019
  2. Martaine2005

    Martaine2005

    2,394
    630
    May 12, 2015
    It’s possible the relay isn’t getting enough current. Check the voltage from the capacitor to the relay. The capacitor may be bad.
    Failing that, post some clear close pics of both sides of the board and somebody here will be able to help you.
     
  3. 73's de Edd

    73's de Edd

    2,678
    1,085
    Aug 21, 2015
    Thir timtam75 . . . . . . . . ( ohhhh my, my I theem to have developed a lispth.)


    Now, in just looking at that board, which just seems to be JUST for the power switching relays and their linear power supply support.
    Top left corner, we can see the two pin Euro connectors with the AC line voltage input and its BLUE and BROWN power input wires.
    It then flows down to catch a BLUE varistor that can crunch up to moderate line spikes, should they come upon the line in times of electrical distress..
    Then it passes to the right to a larger C1 DARK GRAY / or / BLACK ? poly " line trash filter " and then into the primary of the BLACK cased 220 in / 14V out AC power transformer.
    Unviewable to us . . . on the other / under side of the ciruit board, must be a set of rectifiers to generate DC voltage from that raw 14VAC.
    With that given / specified minimal 140 ma current capability, that would not require much filtering, at all.
    Therefore, the filtering would seem to be done by the shown C2 plus C4 black filter capacitors shown at the bottom output side of the transformer.

    The way that relay(s) is / are chattering . . . . in their making an attempt of creating 50 cycles per second . . . .now, certainly one of those filters has failed completely.
    Take your metering and place in DC mode . . . .~50 VDC range (unless autoranging) and read across the larger of the filters (C4) and see what DC voltage you read across the positive and negative terminals of that filter after a powering up of the unit and with the relay chatttering present.

    Then repeat on the metering of the other filter.

    Is one filters developed DC voltage, being appreciably lower than the other ?

    THEN . . . . let's doittoit and subject it to the REAL . . .test.

    Switch to AC metering mode and repeat the two tests, but this time expect a HIGH reading on the inactive filter.

    Thaaaaaaaaaasit

    73's de Edd . . . . .

    How do they know EVERY snowflake is different, and not just being reincarnated each winter?


     
    Last edited: Aug 18, 2019
  4. timtam75

    timtam75

    5
    0
    Aug 18, 2019
    Thanks so much for the helpful education and assistance. This is my ageing parents' range hood. I will go round in the next couple of days, test it and post results.
     
  5. timtam75

    timtam75

    5
    0
    Aug 18, 2019
    Hi 73 de Edd and others

    I have done the testing and this is what I have come back with:

    C5 (small capacitor) DC around 4.5v; AC between 9 and 16v (with one brief peak of 26v)
    C4 (large capacitor) DC around 8.6v; AC between 4 and 10v (brief peak of 18v)

    What do you think? Just replace small capacitor, or replace both at the same time?

    Picture of back of board attached. Just out of interest, what would the big white capacitor be doing?

    Cheers

    Cheers Tim PCB back.jpg
     
  6. 73's de Edd

    73's de Edd

    2,678
    1,085
    Aug 21, 2015
    Sir Tim . . . . .

    Replace both, as the board reads out as using but a mere 1/2 wave rectification scheme.

    As for, the large loose white . . . . hanging . . . .capacitor you did not show its markings, but my first suspicion is being that it is associated with a ventilating fans motor.


    Use a BRIGHT light and a secondary back up use of a magnifier lens to examine all of the solder joints on the boards solder side.
    Thats to confirm that you do not have any present or in progress of developing . . . . solder ring fracture joints . . .a la . . .

    [​IMG]



    73's de Edd . . . .


    The more an item costs, the farther you have to send it for repairs.

     
    Last edited: Aug 19, 2019
    timtam75 likes this.
  7. timtam75

    timtam75

    5
    0
    Aug 18, 2019
    Thanks 73's de Edd

    I will replace both and check soldering on the board.

    I didn't test the large hanging capacitor. There would be different symptoms if that was failing?

    Regards
    Tim.
     
  8. Bluejets

    Bluejets

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    698
    Oct 5, 2014
    Buzz sounds like mains frequency to me.....
     
  9. timtam75

    timtam75

    5
    0
    Aug 18, 2019
    73's de Edd

    You are a gentleman and a scholar

    Thanks for your help. I replaced both the capacitors as you suggested and voila! problem solved.

    I appreciate your help and my parents are chuffed too - they were ready to buy a whole new range hood!

    Regards
    Tim
     
  10. 73's de Edd

    73's de Edd

    2,678
    1,085
    Aug 21, 2015
    OH -TAY ! . . . . . . . .a . . . la . . . . Buckwheat.
     
    Last edited: Aug 23, 2019
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