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Bose amplus 100 amplifier weird noises

Discussion in 'Troubleshooting and Repair' started by refmatt, Sep 23, 2015.

  1. refmatt

    refmatt

    6
    0
    Sep 23, 2015
    Hi

    I have this Bose amplifier that had a number of problems when i got it like no power which i have eventualy sorted, however i now get good sound out of it for about 10 seconds then it sounds terrible like in the video attached, this is at a low volume and with a number of different sources etc.

    If anyone has a clue on where to start that would be great ? Unfortunatly i dont have a scope :(

    Circuit diagram is attached also






    Thanks in advance
    Matt
     

    Attached Files:

    Last edited by a moderator: Sep 24, 2015
  2. dorke

    dorke

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    Jun 20, 2015
    How does the AMP sound in low output volume?
    What was the "no power" problem you found?
     
  3. dorke

    dorke

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    Jun 20, 2015
  4. refmatt

    refmatt

    6
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    Sep 23, 2015
    Thanks for the responce the c
    Volume doesnt seem to make a difference to the sound, it sounds distorted at all volumes. And the no power issue was mainly due to the mains switch essentially falling apart i think due to over use ! So just soldered a new one in :) thanks
     
  5. refmatt

    refmatt

    6
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    Sep 23, 2015
    Thanks for the responce, i will order a 10uf at 50v cpaacitor and give this ago :) it all sounds so easy when people who know what there doing explain things :) thanks
     
  6. refmatt

    refmatt

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    Sep 23, 2015
    Sorry davenn that second comment was ment to be a reply to your first post apologies i thought i clicked on yours.
     
  7. dorke

    dorke

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    Jun 20, 2015
    What is feeding the input of the AMP?
    It should be a differential signal with shild(+,-,GND).

    Can you try and see if there is distortion on the line-outputs(differential as well)?
     
    refmatt likes this.
  8. refmatt

    refmatt

    6
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    Sep 23, 2015
    The input to the amp is a differential signal.

    I have used the speaker scope to test around everywhere i test seems to be distorted the same as the output, when i test tp1 which is just after the resistor it is doing it even though the input when tesed sounds fine through the scope. Does this mean them resistor could be to blame or is this reading false as it is coming from else where ?
    Thank you agian
     
  9. dorke

    dorke

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    Jun 20, 2015
    It looks like some replies are missing from the discussion...
    Please remind me ,what are you finally using for the "speaker scope"?
    In any case, it will be loading the circuit under test .
    If you use it for testing low impedance circuits it may be o.k,
    but for hiZ circuits it isn't.

    If I understand correctly ,
    the signal to the left of R100 is not distorted but the one to the right is.

    No,the resistor is not the cause(but check that it's resistance value is o.k).
    When using the "speaker scope" what was your reference point?

    A general note:
    If the input stage causes distortion ,you will get it in every point along the path till the output.

    The first stage is a differential to single ended buffer.

    Let's check the first stage:
    disconnect the input cable to ch
    1.without power connected to the unit,
    check resistance between G1 and Analog GND(marked by a triangle) for High impedance.
    2.with power on and input cable to ch1 disconnected .
    check U100 pin 1 for zero Vdc (TS1 point)
    check U100 pin 2,3 for zero Vdc (TP3,TP4)
    check U100 pins 4,8 for +/- 12Vdc

    If all the above are good ,use the "speaker probe" but in a differential mode !
    probe between M89-M90 and TP1-TP2,what do you get?
     
  10. dorke

    dorke

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    Jun 20, 2015
    Forgot to say :all Vdc measurements to Analog GND.
    and,Here is the Circuit Stage1.jpg
     
  11. refmatt

    refmatt

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    Sep 23, 2015
    Hi

    Thank you so much for your time i really appreciate it.

    I have firstly measured the resistance between c103 and r104 which i believe are the points you meant, when i first did this it was reading 19.21 kohm then the second few times i did it i was getting roughly 9kohms ?

    As for the u100 on ts1 and tp 2 and 3 there was 0v

    On pins 4 and 8 which i measure on c108 and c106 i was also getting next to 0v it was 0.1 ish and when on mv it was all over the shop.

    I am not really sure what this means ?

    Thanks matt
     
  12. dorke

    dorke

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    Jun 20, 2015
    Pin 4 and Pin 8 should measure +/- 12V DC (with power on).
    If it is zero, you found a meaningful problem.
    Trace those lines they should get to a regulator(s).
     
  13. dorke

    dorke

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    Jun 20, 2015
    Look at the diagram:


    supply.jpg
     
  14. Mapromonyc

    Mapromonyc

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    Feb 14, 2019
    Hi I k ow thinks an old post but I picked up a used amplus 100. After plugging in and turning on the switch I dont get any light to indicate power. Am I missing something?
     
  15. Ylli

    Ylli

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    Jun 19, 2018
    Schematic is available here: https://elektrotanya.com/bose_amplus-100.pdf/download.html
    Start by checking the fuses, F600, F601, and F602. If the fuses are good, then take out your voltmeter and check the voltage on (either end) of both R602 and R603. Should find about +20 volts on R602 and -20 volts on R603. Now check the voltages on the outputs of U600 and U601. Should be +/- 12 volts respectively. If good so far, does it sound like the relay K600 is pulling in?
     
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