Trying to solve signal loss + humming. Also the ground is funny somehow...

Discussion in 'Amp Tech Center' started by PaftDunk5555, May 22, 2020.

  1. PaftDunk5555

    PaftDunk5555 TDPRI Member

    Posts:
    23
    Joined:
    May 21, 2015
    Location:
    Taiwan
    Hi, Tele lovers!
    I have read more than 10 posts about hum and buzz and had try to target the problem myself. But somehow I failed. I will explain it later.

    For a year or so, my amp would occasionally humming very and losing guitar signal at the same time during playing. Even turning the volume down is doing nothing. A trick that used to work is to switch the amp off and switch-on again. Now the trick fails, too. I have change all 7 tube on the amp...no good.

    Two more things to mention: 1. when the problem happens, the blue glowing of output tube will become brighter and easier to see. 2. I found that I can re-create or ease the problem by attaching or detaching ground wire. Let's say, it is humming now, and I can attach the amp chassis to TV cable's outer ring (which is grounded) to change the loudness of humming. But I can't control to make it louder or quieter. It is random. oh yeah, wall plugs in Taiwan are never grounded and the only undoubtedly grounded wire is the the TV cables.



    So, lemme tellya why I fail to target the problem: I found the parts list and the PCB layout:
    https://www.bruynooghe.fr/public/ampli/Schematics_Fender_amp/Vibroverb/63_RI_20Vibroverb.pdf
    However, I find that my board looks different in several places. For instance, the diodes are different and the Cap38 (C38) is not on the layout, let alone the definition of the file is not very good...I was very confused so decided not to do anything until the great Tele lovers show me the way!
     

    Attached Files:

  2. Jon Snell

    Jon Snell Tele-Meister

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    277
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    Aug 31, 2015
    Location:
    Jurassic Coast. UK.
    What is the actual model number as your photo is not the 63 version.
     
  3. tubejockey

    tubejockey Tele-Meister

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    492
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    Nov 25, 2015
    Location:
    the bozone
    Looks like you have the "domestic version". Do you have 120v, 60Hz in Taiwan?

    Intermittent problems in a PCB-style amp are almost always a broken solder joint on the board somewhere. Check the tightness and cleanliness of your tube sockets first, but then you may have to pull the board and check out the solders.
     
  4. Lowerleftcoast

    Lowerleftcoast Tele-Holic

    Posts:
    938
    Joined:
    Dec 30, 2019
    Location:
    california
    Agree with tubejockey above.

    How old is the amp? Possibly the electrolytic caps are giving up.
     
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