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AV Receiver Power diagnosis help please

Discussion in 'Power Electronics' started by Nrose, Apr 18, 2020.

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  1. Nrose

    Nrose

    3
    0
    Apr 18, 2020
    I know some electronics basics, have read some general basic diagnostic info, but otherwise a newbie.

    Symptom: Onkyo AV Receiver. Stopped turning on. Usually hear a light click, but doesn't come on. Took it apart, eventually it came on as usual, louder normal relay click, then display comes on. Worked for a while, then stopped.

    What I've done: assumed it was a bad, finicky relay. Looks like 120v comes in, button activates 12v transformer to switch relay to power larger transformer.


    I bought new exact relay replacement, and replaced. Same thing. Tested voltage at transformer. Seems 120 consistent on high side. 7.8v on low side when off, then 9.8v when on. Ohms on low side, 16, but not sure I'm reading right. Finally got it going by putting 9v battery across relay, big click, power came on.

    Works for a while, can power on and off. But if I completely discharge capacitors, doesn't work until I "jumpstart" it again.

    New relay, so not that.
    Transformer does seem to put out 12v when it does come on.
    Capacitors? Something obvious I'm missing?

    Many thanks for any help, and apologies in advance if I've misposted or commited any other inadvertent forum faux pas.
     

    Attached Files:

  2. Nrose

    Nrose

    3
    0
    Apr 18, 2020
    I feel like a dope. Just realized the white stuff around the capacitor is not glue or supposed to be there. Is this sign of bad capacitor and likely culprit?
     

    Attached Files:

  3. bertus

    bertus Moderator

    1,022
    374
    Nov 8, 2019
    Hello,

    You can more often see some glue like substance around capacitors.
    Sometimes it is a kind of silicon paste.
    It can be for mechanical stability.

    Is the fuse shown on the picture OK ?

    Bertus
     
  4. Nrose

    Nrose

    3
    0
    Apr 18, 2020
    Thanks so much for the quick response. Fuses are all ok. Took out the capacitor. Ordered another just in case. In meantime, had two 1000uf 10v I put in in parallel. I know, not wise to use 10v where original is 25v 2200uf. Nothing blew up, but now doing the same thing. Works if I jump the relay, but not if it's drained.
     
  5. bertus

    bertus Moderator

    1,022
    374
    Nov 8, 2019
    Hello,

    Voltage wise, you should take a higher voltage to avoid problems.
    When a 10 Volts capacitor holds, there must be something else wrong.
    An 10 Volts capacitor on overvoltage will likely blow.

    Bertus
     
  6. Bluejets

    Bluejets

    4,226
    897
    Oct 5, 2014
    This does not seem correct.
    Assume this is an AC reading you have done.
    Notice there is another board adjacent. As well as the main transformer.
    Appears to be 2 LV windings, 2 * red cables and the 2*yellow and black (latter split supply)
    2*orange appear to be primary, details fuzzy as cannot see everything this end.

    Show as much detail as you can and take care photos are not blurry.
    When showing readings, show or sketch out where you are taking these readings and on which scale of the meter.
     
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