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?
     
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  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.
     
  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.
     
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  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.
     
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  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. B String

    B String Supporting Member

    Apr 11, 2002
    Los Angeles
    I hate to be the bearer of bad news, but when that happened on my F500 in late 2019, Markbass replaced my main power board under warranty. (great company) It ended up I may have gotten the last part in the U.S., according to the factory warranty repair shops they use. Still love that head.
     
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  13. MarkA

    MarkA In the doghouse. Supporting Member

    Sep 26, 2008
    Under warranty? Given the age of most F500s, that surprises me!

    I recently had my LMII repaired -- the shop (an authorized Markbass service center in the Chicago area -- I'm blanking on the name right now) was able to source an "old" (new, unused, but older configuration), class AB board for the amp (the newer, class D board would have worked, too). It was most definitely not free, though!

    This isn't directly applicable to the F500 -- I'm just saying that, given the age of the part I got, maybe there is still hope.

    Or maybe, as Andy suggests, the repair can be done relatively simply, without having to swap out the board.

    Option 3: Look out for Jake in the bushes on your way back from your next gig!
     
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  14. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    Contributor- Bass Musician Magazine
    Forgot about this thread! Update is that one 50 cent component was on the fritz. My tech replaced it, now its working great. It also solved a mute pop issue. So the F500 is back in business, with an easy and simple tune up!

    Still loving this amp, its interesting that this one never caught on in the moment, but has achieved an MVP status in the years since.
     
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  15. DWBass

    DWBass The Funkfather

    Was a great amp and very desirable but I think the price put a lot of folks off.
     
  16. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    Contributor- Bass Musician Magazine
    Perhaps so. i dont remember the new pricing. I rocked an F1 for a while when they were new, and it was a great little amp. Well worth the price of admission for the power and tone.
     
  17. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    Contributor- Bass Musician Magazine
    That being said, MB's pricing always seems a bit high to me for what it is, and the competition. great stuff nonetheless. I know its not for everyone, tonally, aesthetically, etc...
     
  18. MrLenny1

    MrLenny1 Supporting Member

    Jan 17, 2009
    New England
    IIRC KJUNG a former TB'er and product reviewer
    loved that amp.
     
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  19. B String

    B String Supporting Member

    Apr 11, 2002
    Los Angeles
    I've been very fortunate to have always had a good relationship with Markbass, although not a signed artist. Marco is a sweetheart. He told me the F500 was one of his favorite heads but they discontinued it because it had to be made so differently from all the other amps, with very specialized parts like the power supply. They were nice enough to give me the last power supply board they had. I paid the labor, which was not much at all.
     
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