Question about Audio Players & Recorders

5 Answers

When i am turning the power on at. channel 1 for a moment pumping (pop) the speaker and is not playing sound. The same pumping (pop) have when i am turning the power off. When the volume level is at minimum no any action (pop) on speaker. Channel 2 is working well. This happened first time when i turned on the amp and before play anything i heard a sound like click-pop with short noise. I have a small video if it helps

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  • 17 more comments 
  • m_mralex Apr 07, 2011

    The amplifier is Behringer A500 just 2 year old (not too old) and potentiometer is working properly.

  • m_mralex Apr 08, 2011

    About reference amplifier Behringer A500
    When i am turning the power on at channel 1 for a moment pumping (pop) the speaker and is not playing sound.
    The same pumping (pop) have when i am turning the power off.
    When the volume level is at minimum no any action (pop) on speaker.
    Channel 2 is working well.
    This happened first time when i turned on the amp and before play anything i heard a sound like click-pop with short noise.

  • m_mralex Apr 08, 2011


    Dear.

    The amplifier is 2 years old (not too old i think) i am hobyist with the amplifiers i mean is not first time i'm working with.

    i don't see any black part on the board. power transistors are working. i didn't had any burnt fuse

    When i am touching the middle pin at the level potansiometer (channel 1) i can hear sound on the speaker(bombination)

    is there a probability to have any burned diode? or any driver transistor? i need your opinion to find the start point.Thanks.

  • m_mralex Apr 08, 2011

    http://www.scribd.com/doc/52592719/Behri... Thanks

  • m_mralex Apr 08, 2011

    hi dear.

    i understand that the power TR's are working properly.When i am touching the middle pin of the volume potansiometer i hear hum sound (i suppose it is normal).is it logical to test first diodes or the TR's before power TR's? Thanks

  • m_mralex Apr 09, 2011

    I saw with an oscilloscope at the output of IC1A pin1, the same pumping waveform,this pumping (clip) this is going to main amplifier and it's amplifying to the speaker but i can't understand where is starting from.Input is free from any source.

  • m_mralex Apr 09, 2011


    i have unplugged now the potentiometer and i saw that the speaker still is pumping in the same way (at start up) but when i'm touching with my finger the cable after the potentiometer i hear(normaly) hum

  • m_mralex Apr 09, 2011


    i gave sound at the middle pin of the potentiometer and i heard normal sound from the speaker

  • m_mralex Apr 09, 2011

    do you mean about T1 - T2 - T3 ?

  • m_mralex Apr 09, 2011

    The oscilloscope is Hameg HM203s it has component tester and as i check the 3 TR's there is no any shorted

  • m_mralex Apr 09, 2011

    ok i'll try it and will keep in touch thanks

  • m_mralex Apr 09, 2011

    As measured the C8 - C9 no any problem i found.Both of them are working properly. Also C17 working properly.

  • m_mralex Apr 10, 2011

    I have removed the C11 and the speaker has stopped pumping!

  • m_mralex Apr 10, 2011

    when i am testing it on the component tester i see that the capasitor is working properly

  • m_mralex Apr 10, 2011

    C17 is replaced but the old was working also

  • m_mralex Apr 10, 2011

    yes but C11 is without polarity...is'nt it?

  • m_mralex Apr 10, 2011

    ok dear. i will replace it tommorow cause here in greece time now is half past 5 at morning and i'll go to sleep.Where are you from what time is it in your country? thanks for your help. will keep in touch till the end of this mission. Best regards.

  • m_mralex Apr 10, 2011


    Dear supertech you're right! At the output of ic1 pin7 there is dc. today is Sunday an as you know market is closed.I found a TL072 and it's now soldered on the board. The size of TL072 is different it looks like monster instead of previous 4580 but i have maked a patent and now the amp.is working perfect! i have posted a foto just for fun to see how Mr. TL072 is hard-pressed.
    http://www.scribd.com/doc/52716788/Ic-Tl...
    Thanks a lot for your help you were very helpful to me, i think my english wasn't incomprehensible.We had very good collaboration Best regards.
    Thanks a lot for your help you were very helpful to me, i think my english wasn't incomprehensible.We had very good collaboration Best regards.

  • m_mralex Apr 10, 2011

    Thanks a lot for your help you were very helpful to me.Now i have fixed the amplifier and it's working perfect!

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5 Answers

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  • Master
  • 1,591 Answers

Pictures would help a lot (of the circuit board)
You're lucky, you have a whole channel for reference!
This means we can troubleshoot by metering points at channel A and cross referencing them with what's happening on channel B (You'll need a multimeter and SOME skill, as well as a soldering iron, solder, desoldering braid and/or a desoldering pump)

When we find something that's way out of spec, we know we've found the issue, or at least something connected to the issue.
If you have an oscilloscope, we can trace the signal to the point that it stops.
If not, as I said, metering mirrored points should lead to the issue.

Posted on Apr 09, 2011

  • 14 more comments 
  • Norman Skinner
    Norman Skinner Apr 09, 2011

    Check your inputs...put input 2 into input 1 and see if channel 1 works then...perhaps the signal going in is the issue.
    If that's not the problem, try feeding a signal into the potentiometer on channel 1 from an old walkman or something that is already pre-amplified.
    if that works, take the same signal, and feed it into input #1, and slowly work past the pre-amplifier stages working towards the potentiometer.
    Once you have sound, you know the stage behind where you are injecting the signal is the problem.
    I can't be too much more specific as your pictures/schematics are too low a resolution for me to make out.

  • Norman Skinner
    Norman Skinner Apr 09, 2011

    I'm betting at the moment on a shorted pre-amp transistor in the input stage of channel 1.

  • Norman Skinner
    Norman Skinner Apr 09, 2011

    Hmmm, I keep getting notification of replies, but I am not seeing any of them...I hope your diagnosis is going well.

  • Norman Skinner
    Norman Skinner Apr 09, 2011

    Put the potentiometer back in then, since we're pretty sure the amp is working past that point, and put a signal into input 1 and use the oscilloscope to trace the signal to where it becomes a non-signal. If you have a high resolution scan of that schematic, email it to FixYa@fake-address.com and I'll be able to get it.

  • Norman Skinner
    Norman Skinner Apr 09, 2011

    Ok, if you have replacements for C8 and C9, I think that may get rid of the "pumping" issue.
    Those are the 3300uF 100V on the output to the + and - power rails.

  • Norman Skinner
    Norman Skinner Apr 09, 2011

    I'd also replace c17 going into channel A's dual preamp chip (connected to pin 5 of the 4580)

  • Norman Skinner
    Norman Skinner Apr 09, 2011

    Ok.

  • Norman Skinner
    Norman Skinner Apr 10, 2011

    Ok, try putting a signal at pin 7 of the 4580 on channel 1 and adjust the volume to see if you get sound.
    If so, reduce the volume (lest you blow off your ears) and put the signal at pin 5 and try again.
    Tell me the results.

  • Norman Skinner
    Norman Skinner Apr 10, 2011

    Right, that's the coupler from pin7 of the 4580 on the pre-amp stage to pin 6 of the next 4580.
    You may also find this is the capacitor that was killing the signal.
    Replace it and I have a feeling it'll all be fixed.

  • Norman Skinner
    Norman Skinner Apr 10, 2011

    basically this would mean I had gone back one amplification stage too far when I said to replace c17 if it works!

  • Norman Skinner
    Norman Skinner Apr 10, 2011

    that's good, because that means you can put the old c17 into the place of the c11 since they are both 10uF 50V.

  • Norman Skinner
    Norman Skinner Apr 10, 2011

    You are correct, sorry I missed that...yes, C11 will need to be replaced with a non-polarized capacitor.

  • Norman Skinner
    Norman Skinner Apr 10, 2011

    If that doesn't fix it, scope the signal from input to output of that first 4580....it's possible the first 4580 itself is blown.

  • Norman Skinner
    Norman Skinner Apr 10, 2011

    It's 11:00 PM here in Ontario Canada.

  • Norman Skinner
    Norman Skinner Apr 10, 2011

    It's actually looking like the A section of IC1 may actually be the problem. (IC1A)

  • Norman Skinner
    Norman Skinner Apr 10, 2011

    LOL...not many would use a DIP to replace an SMT but you pulled it off admirably! Bravo!
    Glad it's all working now!
    That was interesting to say the least!

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  • Master
  • 11,800 Answers

The pop you hear is normal and it's caused by the sharp change in the potential of amplifier when you power it on and off. Since you hear it at top volume only it means that the amplifier itself is functional so the defect is before it: check the preamplifier by imputing a signal directly on the input of the IC2A - if you get sound output you will know for sure.

Posted on Apr 08, 2011

  • Azrael SRL Apr 09, 2011

    Yes, the middle post of the potentiometer is the input of the power amplifier. If you get a loud brum (white noise) when you touch it it means that the power amplifier and the main power transformer are operational. This means that the preamplifier and/or the input selector is not working, those are the ones to check, not the power transformer. BTW the Scribd schematic is set to private, it cannot be seen.

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  • Master
  • 2,098 Answers

HI m_mralex,
Upload the schematic diagram here to assist you where the possible caused of symptoms came from. Then give me the link, the schematic can't view clearly...
Jdvillanueva

Posted on Apr 08, 2011

  • Jdvillanueva
    Jdvillanueva Apr 08, 2011

    sorry for the late reply, the document you've uploaded was set in private, I can't get an access...




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  • Master
  • 3,018 Answers

Hello,
Sounds to me like it could be a couple things. First open the amp and on the bad side check for any black on the circuit board and also check the board for cold soldier joints. Check real good where the RCA plugs plug into. Any black would indicate a need to replace that component. Have you tried switching the RCA cables around to see if it is a bad side on the RCA cables? Popping is usually associated with voltage "arching" that happens because of a bad electrolyte capacitor inside your amp. I have to advise that if you have never worked with electronics and have never worked with capacitors you should have a technician address this. Capacitors store massive amount of energy in them plates. Touching them before a discharge could be fatal.
Regards, Tony

Posted on Apr 08, 2011

  • 2 more comments 
  • Iron
    Iron Apr 08, 2011

    As I stated above, popping is almost always arching of a bad electrolyte capacitor. If you have a capacitance meter you can test them.

    Regards,
    Tony

  • Iron
    Iron Apr 09, 2011

    You can spray some freeze in a can and see if the transistors go crazy. That would indicate a need to replace them. Also the hum is not normal at all. You should not get a hum unless you are grounding the potentiometer.

  • Iron
    Iron Apr 09, 2011

    To physically test the transistors you would need to remover them and check them accordingly depending on weather they are NPN or PNP with a multi meter.

  • Iron
    Iron Apr 12, 2011

    As I stated above "Popping is usually associated with voltage "arching" that happens because of a bad electrolyte capacitor inside your amp."

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  • Master
  • 1,622 Answers

Well, the knob for your amplifier is not working properly as it seems..you have your finger on the source of the problem. If accessible, try some tuner cleaner inside the potentiometer.
And it will be fine,,

Take care..

Posted on Apr 07, 2011

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