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Turn on after 3 seconds turn off

Discussion in 'Electronic Repair' started by donskister, Dec 2, 2006.

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  1. donskister

    donskister Guest

    I went to my friend he ask for my help if i can repair his kenwood
    model RX-39 audio system. I turn on the power then it seems the unit
    have no problem but after 3 seconds the unit turn off and the message
    appear on the display ( Protect )..I noticed after repeatedly turn on i
    hear a clicking sound inside the unit before the unit turn off..I plan
    to open it by next week so that i can first gather informations before
    i try to repair it.

    By the way... My friend told me that sometimes he can used the unit
    for a couple of months when he will not used the unit for a weeks then
    after the unit will fail again then he will not used the unit for a
    weeks..... it seems that the unit is working if had taken a rest.
     
  2. James Sweet

    James Sweet Guest


    It could be a cracked solder joint, you have to be careful working on
    audio amps, sometimes the protection circuit will save them, sometimes
    they suffer a catastrophic failure and then you're looking at new output
    transistors and a whole pile of parts they take out when they blow.
     
  3. budgie

    budgie Guest

    I'd suspect a speaker load problem.
     
  4. Morse

    Morse Guest

    My guess would be failing capacitors causing DC leakage and upset bias in
    the audio path or something similar.

    It needs attention as using it in this condition and repeatedly trying to
    power it on could cause expensive damage.

    Morse.
     
  5. I agree. Check the speaker wires for shorts.
     
  6. Arfa Daily

    Arfa Daily Guest

    Some of the old Kenwoods used to have trouble with the delay cap in the
    protect circuit, leaking. As the problem is intermittent, might be worth a
    look, but otherwise, as others have said, good first place to look is at the
    speakers and their wiring.

    Arfa
     
  7. donskister

    donskister Guest

    Thanks guys for your advised il be visiting my friend house this week
    to check it again...i will post immediately what happen when i check
    it.. i hope you help me guys till the end to repair my friend
    equipment ....thanks in advance
     
  8. Guest

    I'd go with the delay cap too. Isn't that typically a low value
    electrolytic in the relay turn on circuitry?
    Jango.
     
  9. Arfa Daily

    Arfa Daily Guest

    It is. I've had more than a few over the years.

    Arfa
     
  10. Morse

    Morse Guest


    I wonder if the correct impedance speakers are being used? It's not that
    uncommon for people to think it's OK to just bung any old speakers onto an
    amp, and end up with 4 Ohm speakers on an 8 Ohm system, causing shutdowns.

    The OP said the system works after 'taking a rest', which is why I suggested
    an amp fault. A lot of amps will shut down when there is DC present on the
    speaker terminals, even though the sound may appear normal.. I'd expect most
    people not cursed with cloth ears to pick up on faulty speakers or wiring-
    the sound would be low, distorted or non-existent. Mind, I've seen
    situations where people were totally unaware of a dead audio channel so
    anything's possible!

    Morse
     
  11. Arfa Daily

    Arfa Daily Guest

    A couple of years back, I had a speaker that supposedly caused an amp to
    shut down intermittently, and particularly on one specific piece of music,
    which the customer obligingly supplied. I was of course sceptical, but the
    owner insisted that he had proved beyond doubt, that it was the speaker.
    When I tried the system out, both speakers sounded fine on the music I was
    playing, but when I put on his offering, the system immediately started to
    intermittently shut down. The cause finally turned out to be bass-related,
    but not for any conventional speaker fault that you would hear on any old
    passage of music, or even if you turned it up loud. It was actually due to
    one of the braided flexible tails that go between the cone and the
    connection tag board. A number of the strands had fractured at one end
    through metal fatigue, and had come unravelled. This left them flying around
    in mid air. On most music, and at most drive levels, this was of no
    noticeable consequence. However, on the offending piece of music, on certain
    bass passages, some kind of resonance was hit, and the free strands flew
    about like things possessed, and intermittently touched the other tail,
    resulting in a momentary short across the amp, which then caused its
    protection circuit to shut it down for a few seconds.

    So whilst I absolutely agree that normally, defective speakers or wiring
    would be easily heard, it's not always the case ... ;-)

    Arfa
     
  12. budgie

    budgie Guest

    Oddly enough, I had a shutdown/incompatiblity issue about 20 years back, with an
    Akai amp driving Mission 700 speakers. The Akai spec was "minimum 4 ohms".

    The 700's sounded fine in the showroom, and could be driven hard by their amp.
    At home, anything above modest level with certain material caused the amp
    protection to intervene. Eventually got the impedance curves for the 700's and
    found there was one sub-1khz area where the impedance dropped to ~2.5 ohm.
    Tests with a signal source proved the susceptibilty, and the Missions were
    returned.
     
  13. donskister

    donskister Guest

    Hi Guys...

    I just came to my friend place yesterday to repair his audio system
    with full of knowledge thru the tips I gathered to all of you guys (
    Checked for cracked solder joint, speaker wiring, failing capacitors in
    the protect circuit... I confirmed that when I checked his audio before
    theres no speakers connected so I plug the cord on the outlet and turn
    it on again same as before the unit shut off after 2 to 3 sec, I
    cleaned the connector by tipping using my finger to cleaned the
    connector outlet before we connect the speakers on the unit then we
    turn it on the unit does not shut off so we play a cd to test its
    working! But we noticed that when we turn up the volume the unit shut
    off( protect) so we try it again to know what level of volume the unit
    shut off its seems that the unit seems working if only set below 35 (
    note. Max volume 60 ). After that we dismantle the unit to check the
    components of power supply hoping to find fail components by visual
    check up then and again slap a little the connector pin of the speaker
    to cleaned hoping to remove the one that causing the shut off if any .
    After we assemble the unit we connect the speakers and turn it on its
    working so we decide to turn up the volume above 35 the does not shut
    so we adjust it to 40,45 and 50 the unit does not shut off. Im happy
    that I successfully fixed his unit. But Im confused what really the
    caused why that unit behave like that?????? and How I repaired that ,I
    only disassemble the unit?????

    Don
     
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