Power Amp Troubleshooting help

Discussion in 'Analog & Mixed-Signal Design' started by BenPhan, Jun 17, 2011.

  1. BenPhan

    Thread Starter New Member

    Jun 16, 2011
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    Hello forum,
    I got a power amp named "PhuongAnh Amplifier" model: PA 9800 which I could not find the company info in order to acquire service manual anything. The problem is that the amp looks working by seeing the light panel in front. However, there is no sound at speakers. One time in the past, the amp was playing, all of a sudden, the amp shut off itself and since then the problem came into life. I opened the cover, seeing wires everywhere. Tracking the wires from spks terminals to one of pcbs, there is a relay called "JZX 18FF" and I wonder that could this be one of the components of spks protection system, if it is, where do I start to determine that the relay went bad or any other related components in spks protection system went bad?
    Gentlemen, shed some light to help solving the problem.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    282
    If you have no schematic - that is very common - then troubleshooting gets a bit tedious. The minimum tool you need is a multimeter. Do you have one?

    If so what are the various voltages produced by the power supply? Do any output transistors get hot?
     
  3. BenPhan

    Thread Starter New Member

    Jun 16, 2011
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    Thx for reply Beenthere, yeap, I got a multimeter. the supplies are 45v, 15v and 12v. I am reading those out of the transformer. No output transistors did get hot Beenthere.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    It's always best when one channel goes so you have the other to compare against.

    Is there any change the "PA 9800" might refer to a PA amp, rather than a stereo amp?
     
  5. BenPhan

    Thread Starter New Member

    Jun 16, 2011
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    At first I thought "PA" stands for Power Amp, but it is Karaoke Amp, 800w @ 8 ohms load. "PA" I think, stands for "Phuong Anh" model of 9800. I am not sure BeenThere.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    We have no idea what that amp might look like inside. Can you supply some clear pictures (PNG format preferred) of the interior?

    Have you looked for the obvious, like bad fuses and burned resistors and swollen capacitors?
     
  7. BenPhan

    Thread Starter New Member

    Jun 16, 2011
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    Absolutely new to this situation, I go a hard time to upload my pictures Beenthere.
     
  8. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    945
    May seem silly to some people here, but have you tried connecting a different speaker that you know is working? Is possible the speaker coil overheated and opened and nothing is wrong with the amp.
     
  9. studiot

    AAC Fanatic!

    Nov 9, 2007
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    513
    Hello Ben

    You say you think this is a stereo amp. Presumably you can find two sets of speaker terminals and input sockets?

    You said you have a multimeter.

    You say that neither channel is working. Normally you look for something that affects both channels ( is common to both) when this happens such as the power supply.

    Have you tested the power supplies ?

    The next thing to look for would be two channel preamp or driver integrated circuits that might have blown.
     
  10. alim

    Senior Member

    Dec 27, 2005
    113
    1
    Hi the relay you mentioned is used for speakers protection, did you hear a click from the relay when you apply power, if you did, this would suggest that the relay activated, and would connect the output to the speakers. If you hear no click from the relay it would suggest the amplifier is protecting itself, and the cause would have to be determined, so make a determination if the AMP is protecting itself.
     
  11. BenPhan

    Thread Starter New Member

    Jun 16, 2011
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    Thanks for guiding gentlemen, I'll upload pictures so that you can have a see what's inside alright.[​IMG]
     
    Last edited: Jun 21, 2011
  12. BenPhan

    Thread Starter New Member

    Jun 16, 2011
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  13. BenPhan

    Thread Starter New Member

    Jun 16, 2011
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    Yah, the power suply rails are there (-30v, +30v) Studiot. And again, equalizer light in front panel jump up and down looking like it's working, but no sound out to a sure working spks. Studiot, take a look at the pictures, show me how to particularly check the output and which board contains the preamp circuits.
    http://s1196.photobucket.com/albums/aa417/BenPhan/
    Thx in advance Studiot.
     
  14. studiot

    AAC Fanatic!

    Nov 9, 2007
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    I'm sorry to have to tell you that although your pictures are very clear, they do not show much of use.

    Close ups of the 4 devices on the aluminium heatsink, showing type numbers would be useful, as would a similar shot of the other heatsink.

    You will need to measure voltages at the three connection leads to each of these devices. Great care needs to be taken to avoid shorting across these leads with the probe.
     
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