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Discussion in 'Troubleshooting and Repair' started by HellasTechn, May 17, 2016.

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  1. HellasTechn


    Apr 14, 2013
    Hello friends !

    I have a weird problem with this Hitachi htd-k150 home cinema system.

    It works all right but some times when i power it on i get noise from the speakers and then i can no longer control volume. It either play sound at steady low volume or not at all. when i press the volume + and - buttons the display shows the volume level but the speakers nothing.

    At firast i thought that it's amplifier IC's may be bad so i replaced them (TDA 7497) but that did not solve the problem. Later i noticed (with the o-scope) the presense of a 150-200mv saw tooth signal between the heatsink and the metal case of the powersupply 6.800uf filter caps.
    Then while still probing that weird signal i tried to raise the volume and after hearing noise from the speakers it started working normally.
    After a few power on and shut down cycles the problem came back and i was only able to eliminate it by placing the o-scope probe same way as before.

    I also noticed the same weird signal on a number of other caps.

    i will post o-scope pictures tomorrow.

    Could it be that theese caps need to be replaced ?
  2. HellasTechn


    Apr 14, 2013
    It gets more and more weird.

    While mulfunctioning
    Probing cap 1 cell to heatsink i get the wave i mentioned before but probing from cap 2 cell to heatsink i see -17 volt DC...

    Attached Files:

  3. HellasTechn


    Apr 14, 2013
    That was just random.
  4. HellasTechn


    Apr 14, 2013
    What i have noticed is that when switching off and back on useing its mains switch some times makes it work correctly.

    I am confused. I suspect that power supply section may be the problem. I will read the repair manual and see.
    Last edited: May 18, 2016
  5. shrtrnd


    Jan 15, 2010
    I'd recheck my mechanical connections to the speakers before troubleshooting your amplifier.
    It sounds like a problem with the amp, but it sounds like the amp protection mode is kicking-in, and that may be
    a problem with the load (speaker) connections.
    I do the simple, before baffling myself with the technical.
  6. JonG


    Feb 10, 2017
    Hi Constantine,
    Did you get anywhere with this problem ??
    I have an HTD K150 with exactly the same problem !!!
    Although this is an "old technology" system it otherwise works well and would prefer to repair than replace - so any help/guidance/prior experience would be much appreciated.

    Best Regards
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