Diagnose my F500

Discussion in 'Amps and Cabs [BG]' started by J.Wolf, Jul 31, 2021.


  1. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    Contributor- Bass Musician Magazine
    This Markbass F500 head has been acting up recently in a particular way. Wondering if anyone has any ideas about what might be wrong with it. it basically works perfectly in every way, except that there is what sounds like constant crackling/static noise in the background. The tone shaping and filters seem to affect the quality of the static so it seems to me like it's being introduced before the tone stack. the volume of the crackling is tied to the master volume but not the input gain, i.e. the static volume doest change with the input gain knob. It almost sounds like a scratchy pot or a bad cable but clearly is coming from inside the amp.

    Because it's an older unit and I'm not even sure about serviceability of these, I figured I would just throw this up on talk bass to see if anyone more savvy than me might know what to do next with this. thx.
     
  2. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Before anybody diagnosis this as bad caps, let’s dismiss that myth ;)

    Does the noise disappear with the effects loop set to serial position and a signal inserted into the return jack?
     
    REV and rodl2005 like this.
  3. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    Contributor- Bass Musician Magazine
    Thanks for your help Andy! Yes I just double checked and with the jumper set to series it is still producing the noise regardless of what's coming or going from the effects loop.
     
  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Ok, the noise is being generated after the effects loop.

    Does the noise go away with the master volume control?
     
  5. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    Contributor- Bass Musician Magazine
    yes the noise is controlled by the master volume.
     
  6. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Ok, so the fault is confined to a relatively narrow area that should be straight forward to troubleshoot and repair for a qualified service tech that has the necessary documentation. We know that it's not the power supply, the power amp or the input gain stage.
     
    SirMjac28 and J.Wolf like this.
  7. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    Contributor- Bass Musician Magazine
    Gotcha. I do have a guy here who I trust, so I'll take it in. Was just trying to get a sense of how bad/expensive it potentially is.
     
  8. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Provided he has the documentation, it shouldn’t be too difficult.
     
    SirMjac28 likes this.
  9. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    Contributor- Bass Musician Magazine
  10. ahc

    ahc

    Jul 31, 2009
    No. Virginia
    Feel not like the lonesome stranger @J.Wolf. My F500 died about a year and a half ago. Turned it on and it went "brrzzzippp" and got a stinky chemical smell. I turned it off immediately. I too would like to get it fixed but I don't know if the cost/benefit ratio will be favorable. Covid has kept me from finding out. I liked that amp.
     
  11. john m

    john m Supporting Member

    Jan 15, 2006
    Might be a connection in the speaker cable
    “Path”, that is working it’s way loose.
     
  12. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
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