Airis L147 having humm problems

Discussion in 'General Electronics Chat' started by Elokuu, Dec 6, 2013.

  1. Elokuu

    Thread Starter New Member

    Aug 29, 2012
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    Moderators note:
    These posts where split from the following thread:
    Amplifier plays loud humm


    Hey there,
    I just gonna hijack this thread because my problem is quite similar. A few days ago I found an home cinema amplifier and two speakers and I thought maybe I can fix it. The amplifier is called Airis L147.

    When I plugged everything in I just heard a hum, so i unplugged it and opened the case. I thought I detected two broken capacitors and I replaced them. However, after I plugged everything in again, I still have the humming. The humming is not effected by any controls, I actually unplugged all controls and LEDs and the humming is still there. Th circuit looks OK (for me):

    top:
    http://s28.postimg.org/k9tyoymr0/IMG_8473.jpg
    bottom:
    http://s11.postimg.org/5hgmclyk2/IMG_8470.jpg

    From one of the UTC2030 Amplifier is a little bit missing, but I don't think that is the problem:
    http://s9.postimg.org/8l1c0ygq6/IMG_8478s.jpg

    I exchanged the two big capacitors and also checked the smaller capacitors (by measuring).

    any idea how to find the problem?

    Thanks
     
    Last edited: Dec 7, 2013
  2. MrChips

    Moderator

    Oct 2, 2009
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    No. Don't hijack someone's thread with a different problem.
    There is a big difference between hum and motor-boating.
    Is your hum line-frequency hum?
     
  3. Elokuu

    Thread Starter New Member

    Aug 29, 2012
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    Oh, sorry. I just though because the thread is called "loud humm". Should I start a new thread?

    When I record the hum with the phone and I look at the spectrogram it looks like the hum is at 50Hz, 100Hz, 150Hz aso. But it has the biggest magnitude is at 100Hz and 200Hz.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    Don't start a new thread. A mod will move these posts.

    Yes, what you have is 50Hz line frequency hum.
     
  5. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Your photo shows a blown IC amplifier UTC2030, maybe similar to a TDA2030 power amp IC.
    This definitely IS a problem. Replace it. Can you find a schematic??
    Sometimes a pair of these chips are used in a bridged configuration. I would recommend replacing both chips if that is the case.

    The hum around 100 hz is the ripple at 2x50Hz. This is very typical of a blown (shorted) power amplifier.

    Don't run it very long like this or you risk destroying the speakers on that channel.
     
    Last edited: Dec 6, 2013
    Elokuu likes this.
  6. Elokuu

    Thread Starter New Member

    Aug 29, 2012
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    Thanks a lot for your reply,

    Unfortunately I can't find nearly any information on this amplifier. But I found that it is a 5.1 system with 30W subwoofer and 10W satellites. There are 7 amps in total (5*UTC2030 + 2*TDA2030A). So I guess each satellite has it's own UTC2030 and the subwoofer two bridged TDA2030A. But if just one amplifier is broken why do I get a hum on all channels?

    Do you think I can just remove the broken amplifier without replacing it? I have anyway just two speakers and don't have a replacement amp.

    Thanks

    UPDATE: I removed the broken amp and it's still humming :(
     
    Last edited: Dec 6, 2013
  7. tubeguy

    Well-Known Member

    Nov 3, 2012
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    I have to go for now. But see if you can google a schematic.
    Do you have a volt meter or any other test equipment ?

    EDIT: Google for TDA/UTC 2030 datasheets. Then follow the speaker output pins (on the PCB) to see if another IC is in fact
    bridged with the blown IC. It's also possible multiple amp IC's are blown because someone connected too many speakers etc...
     
    Last edited: Dec 6, 2013
  8. Elokuu

    Thread Starter New Member

    Aug 29, 2012
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    Thanks a lot.

    I have just a multimeter. But I'll try to figure out the schematic tomorrow and then get back to you. Thanks
     
  9. Elokuu

    Thread Starter New Member

    Aug 29, 2012
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    Hey,

    So I "analysed" the circuit as good as I can and I can't see any connection between the different amps. Every amp for the sattelites seems to have it's own circuit:
    http://s9.postimg.org/pvt2re2xq/schematic.jpg
    which is very similar as the schematic shown in the datasheet. The subwoofer uses 2 bridged amps. Here is an overview:
    http://s10.postimg.org/l45tb2src/overview.jpg

    Any idea how to move on?
    And I also have a more general question. How is the volume actually controlled? As the input goes straight into the UTC2030 and from there the output goes straight to the speaker output. Does the control panel controls just the "GND" of the input?

    Sorry, but I'm new to all this :confused:

    Maybe I also should also mention that the subwoofer doesn't hum, it's just every sattelite channel. I also disconnected the control panel, LED, subwoofer and inputs and it's still humming. And even when I connect everything, the subwoofer does not hum, but doesn't play any music either.

    Thanks
     
  10. MrChips

    Moderator

    Oct 2, 2009
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    What is used to power the amp?

    It appears that something is drawing too much current and loading down the power supply.
    I think your subwoofer section is dead.

    Unsolder the two subwoofer amps and the broken one beside it and test again.

    Edit: You can do a finger test and feel which amp is getting hot.
     
  11. Elokuu

    Thread Starter New Member

    Aug 29, 2012
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    Thanks for cleaning my mess and opening this new thread. And thanks for the suggestions.

    The amp is powered by a transformer:
    MODELL: PT66V1102600
    I/P: AC 220V 50Hz
    O/P: AC 11V x2 2.6A

    I removed the two subwoofer amps and the broken one, but I still get a hum on all the channels. Except one, which is the one where I removed the amp.
     
  12. MrChips

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    Oct 2, 2009
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    When the new thread got created we lost the photo showing the top view of the board.
    Can you post it again?
     
  13. Elokuu

    Thread Starter New Member

    Aug 29, 2012
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  14. MrChips

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  15. MrChips

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    Maybe the diodes in the bridge rectifier are bad.
     
  16. Elokuu

    Thread Starter New Member

    Aug 29, 2012
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    Just checked the diodes and they seem to be OK
     
  17. MrChips

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    You did say that you replaced the two 4700μF power supply filter capacitors?
     
  18. Elokuu

    Thread Starter New Member

    Aug 29, 2012
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    Yes, that was the first thing I did.
     
  19. MrChips

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    Are any of the remaining amps getting hot?

    Can you detect any excessive heat being generated from any of the components?
     
  20. Elokuu

    Thread Starter New Member

    Aug 29, 2012
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    I tried all the amps, the caps and the 4558D, nothing gets hot, not even warm. Can I somehow check if the power supply is working properly?

    There are three wires coming from the power supply (1xblack, 2xyellow). From black to yellow I have 11.9V and 12.4V. From yellow to yellow I have around 24V. After the rectifier bridge I have 31V.
     
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