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KLH R3100 stereo receiver volume won't adjust

Discussion in 'Troubleshooting and Repair' started by bbullsj, Nov 28, 2018.

  1. bbullsj

    bbullsj

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    Nov 28, 2018
    I have a KLH R3100 stereo receiver. I went to turn it on one day and the volume wouldn't adjust. The knob spins fine and the numbers on the display change but the sound does not increase or decrease. Currently it is stuck at very low. Any ideas on what could be wrong or how to possibly fix it?
     
  2. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    I've never worked on one but my guess is either the rotary encoder or its interface chip.
    If your careful you may be able to take the encoder apart and clean it.
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    But if the
    it looks like the encoder works fine and trouble is with that part of the circuit that translates the amplitude setting into variable gain for the audio signal.
     
    davenn likes this.
  4. Bluejets

    Bluejets

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    Oct 5, 2014
    Remote may be set to some obscure setting.
     
  5. bbullsj

    bbullsj

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    Nov 28, 2018
    I don't have a remote for it. What does the encoder look like and how would I take it apart?
     
  6. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    It looks similar to a potentiometer and is located behind the volume knob.

    I wouldn't rip it apart just yet.
    A valid point was raised by Harald Kapp;
    If the volume display reads out up/down consistently (incremental numbers) while turning vol knob. The encoder is probably fine. Otoh, If the numbers jump around it could be bad/dirty.

    Take some pictures of the circuit board and perhaps we can narrow it down. Digital stuff can be hard to diagnose without a scope.

    Any chance you've got a schematic?
     
  7. bbullsj

    bbullsj

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    Nov 28, 2018
    I don’t have a schematic for it. It doesn’t jump around and works like normal, just no change in volume. Attached are a couple pictures of the circuit board and knob.

     

    Attached Files:

  8. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    @bbullsj, I don't know your skill set or your understanding of electronics, but honestly, you might be better off just having it serviced by a pro.
    Without a schematic and proper test equipment it may be very difficult/nearly impossible to fix. Not to mention you and the forum may need the patience of Job.

    My knowledge is limited, but here's my take on where to look if you still want to tackle this:
    The encoder has two outputs seen in the traces seen in the blue circle of the (one) picture you posted.(as well as a third ground pin.)
    If you follow them they likely go to a interface chip that decodes the volume encoder position and then likely outputs to a op amp chip that changes the gain (volume) to the final amp. There may be a separate ic for the digital display, or they may all on one chip.

    You could start by writing the numbers on the ic's you think may be related to the volume circuit. A google search of them should find out their function.

    With no schematic you'll likely need to draw out the component connections by following the traces on the pcb like a roadmap until you can understand how it works.

    You may get lucky and find the problem without much ado, but if they are surface mount (smd) you will of course need hot air soldering abilities to replace them.
     
  9. kellys_eye

    kellys_eye

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    Check on YouTube for videos related to this model. There's at least one that discusses repairs of it.
     
  10. bbullsj

    bbullsj

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    Nov 28, 2018
    I am trying to fix it instead of buying one. It was my brother in laws and he takes really care of his stuff so I don't believe it's not working because of misuse. If it doesn't end up being an easy fix I will probably just file it in my scrap pile. Looks like I can buy an identical or similar one for around $50.

    So, sounds like that the encoder is good since the volume numbers are moving up and down correctly when the knob is moved. I am a certified auto technician so i'm fairly good with electrical, just not electronics and circuit boards, and related terms. You used a lot of acronyms that went way over my head, lol.

    Does IC mean interface chip? What about PCB?

    I'm a fair solderer but have not heard of hot air soldering. I will start drawing up a diagram this weekend of power flow and trying to see if i can locate the interface chip. What will it look like? Is the interface chip something that can be replaced or is it part of the board?


     
  11. Harald Kapp

    Harald Kapp Moderator Moderator

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    Electronics slang ;)
    IC = Integrated Circuit, those little black bugs on the PCB
    PCB = Printed Circuit Board, that (usually) green "plastic" carrier for the traces and the ICs (to close the loop).
     
  12. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Perhaps a close up picture of the square "black bug" IC that connects to the encoder traces would help.
    Better yet, Take one from the top so we can read the numbers, and one from the bottom so we can see which way the traces go.
     
  13. Bluejets

    Bluejets

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    Oct 5, 2014
    I'd be taking a wild punt and say it has nothing to do with encoder or the big fat 30 pin processor chip and more to do with amp signal input somewhere, perhaps even common power supply problems.
    Thing is it is cheap to begin with so how far does one go really.
     
  14. Tha fios agaibh

    Tha fios agaibh

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    Well, it's a good unit to learn on. Through hole components should be easy to solder with plenty of room, and if you screw something up it wouldn't be much a loss.

    I would think if the amp signal input was bad only one channel would be out or low.
    I guess it depends how low the volume is.

    A likely suspect is those 4558 opamps that could control the gain.
     
  15. bbullsj

    bbullsj

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    Nov 28, 2018
    So it won’t let me upload any pictures. It just keeps saying that a problem has occurred. Any ideas?

    One thing I did notice upon more inspection is that the bottom right hand corner of the screen has a dark burn mark under the glass. Could that be related in any way?
     
  16. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Try pasting the picture from the clipboard directly into the text entry box.
     
  17. bbullsj

    bbullsj

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    Nov 28, 2018
    So, I tried to upload a picture from many different formats (7) but nothing will upload. It still says that there was a problem. I'm guessing it's file size but I don't know any other way to make it small to be able to post it. Guess i'm sunk.

    The volume is stuck at a very low level. I don't know the number because when you move the dial it does move up and down. Whats are the 4558 opamps? What dot hey look like and can I test them?
     
  18. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir bbullsj . . . . .

    If you are trying to use the radio as your sole signal source for testing, it may have a problem with it.
    There are also options for OTHER signal inputs, try one or all of them to see if they put out a full audio spectrum level of adjustment on THEM .
    Or if they respond just as the present test source does.

    I find nothing current on this KLH model, as they now seem to be a Chinee product, riding on the OLD renown KLH name sake.
    BUT . . . . up in post #13's evaluation, he likes its sound . . . but knocks the built in receiver . . . me . . . I LIKE the units honeycomb heatsink .

    73's de Edd
    . . . . . . . . . .

    Last week I bought a new phone. I took it out of the box, hooked it up to the wall . . . pressed redial. . . . .
    and then the phone proceeded to have a nervous breakdown.


     
    Richard9025 likes this.
  19. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    I'm currently experiencing the same issue. I brougt it to the site managers' attetion. We'll have to wait for a fix. Usually it doesn't take long :)
     
  20. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    @bbullsj Uploading and pasting images should now work again. Sorry for the inconvenience.
     
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