Sony amplifier problem

Discussion in 'General Electronics Chat' started by Nick_G, Dec 17, 2006.

  1. Nick_G

    Thread Starter New Member

    Dec 17, 2006
    5
    0
    Hi all.

    I'm a new member and I'm hoping to get some help and advice on an intermittent problem.

    I have an 8 year old TA-FB930R amplifier and occasionally I get the relays for the speaker selector (Speakers A , B etc.) clicking rapidly for no apparent reason. When this happens the sound through headphones cuts in and out.

    Is this a simple problem like dirt on the relay contacts or the signs of a bigger fault?

    I'm not knowledgeable about electronics so any help or advice much appreciated.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Your speaker protection relays might be "seeing" a DC voltage, which is a no-no for healthy speakers. Without seeing a schematic, of course, I can't be sure. You are probably looking at a repair or a new amp.
     
  3. Nick_G

    Thread Starter New Member

    Dec 17, 2006
    5
    0
    Hmm, that does not sound good.

    When it has done this before, giving the amplifier a sharp tap also causes the relay to switch. This is what made me wonder if it is a dirty contact behind the selector switch, or a dodgy connection somewhere.

    Is this also likely?
     
  4. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    Dry joints are a definate possibilty.
    Resoldering the PCB around the relays, the protection sense circuitry, PSU regulator components and the Micro may be a good start.
    Larger components, and hot components (like Relays, power transistors, regulators, power ICs, anything mounted on a heatsink etc etc) can be prone to the dreaded dry joint.
     
  5. Nick_G

    Thread Starter New Member

    Dec 17, 2006
    5
    0
    So if it is dry joints does this mean that the speakers are getting a DC voltage or is it just the relays? I don't want to damage my speakers as well.

    Once the relays have started clicking it also seems to aggravate the problem when switching the speaker selector, so I assume it is the selector that is at fault.
     
  6. Sirropo

    New Member

    Nov 24, 2006
    3
    0
    By dry joints, I'm sure reference is to bad solder joints or the socket the relay
    module plugs into (if it does).

    Its a excellent point to check.
     
  7. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    Sorry, I thought the term was universal. Yes, a Dry Joint is a bad solder connection of a component or lead on a Printed Circuit Board, caused by heat, vibration, or poor preparation of the joint.... often can be seen as a small dark ring in the solder around the through pin.
     
  8. Nick_G

    Thread Starter New Member

    Dec 17, 2006
    5
    0
    Hi all.

    Just thought I'd resurrect this with a quick update:

    I've had the amp looked at by a qualified electronics engineer. He found several dry joints on & around the selector switch and fixed them. However, the problem is still there.

    I'm wondering whether I should just give up & look for a replacement.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    That is purely up to you - the problem can arise from causes other than poor solder joints. I'm still using a 35 year old amp with no problems outside of the input selector switches.

    Doing more than recreational resoldering might take a schematic to be productive, though.
     
  10. techroomt

    Senior Member

    May 19, 2004
    198
    1
    the protection relay typically energizes when a certain dc offset is reached on your amplifier outputs. often, a dc offset adjustment can be made to reduce the offset. you will need a service manual for your amp, they can be found on the web, do a search.
     
  11. Nick_G

    Thread Starter New Member

    Dec 17, 2006
    5
    0
    I don't think it is the protection relay as the protection indicator doesn't light up. Also, I still get audio from the speakers - it's just the sound in the headphones that cuts in & out as the relay switches on & off.
     
  12. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    Sounds like more dry joints the tech might have missed. Sounds like this machine may attract them.
     
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