Fender tweed bronco amp fart.

Discussion in 'Amp Tech Center' started by Anthonyraywright, Oct 13, 2021.

  1. Anthonyraywright

    Anthonyraywright TDPRI Member

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    Hello I'm having trouble with this 90's tweed bronco amp farting out on the clean channel starting around volume 5 when I play the low E and A strings or anything on the frequency. The speaker has been replaced a new exact replacement and the sound still continues I took the back off and looked for loose screws or anything that might cause a rattle and didn't find anything. Any help would be appreciated, thank you.
     
  2. 985plowboy

    985plowboy Poster Extraordinaire

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    Has it always been farty, or is this a recent development?
    Bass up too high?
    Did the old speaker fart out too?
    Is this the little solid state version?
    Maybe you are asking too much of it.
    Fart fart fart fart fart.
    Fart.
    Almost got it out of my system.
    Pun intended.
     
  3. Anthonyraywright

    Anthonyraywright TDPRI Member

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    It's a new fart, with the bass all the way down it still farts, the old speaker did fart, it is the solid state version. I'm almost certain it is a problem in the circuit. I forgot to add that I used it with a bass cab with 2x12 and it still farted.
     
  4. NTC

    NTC Tele-Holic

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    How old is this amp?
     
  5. Skyhook

    Skyhook Tele-Holic

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    Epic thread title though. :lol:
     
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  6. Boreas

    Boreas Poster Extraordinaire

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    I might start searching for a new amp. I don't know how serviceable those amps are. It may cost more than it is worth to diagnose it, let alone fix it. It doesn't sound like a speaker problem to me, especially if you have already tried it.
     
  7. archetype

    archetype Fiend of Leo's Ad Free Member

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    A Bronco PR 258 is a decent amp when run through a separage speaker cabinet. The bass is typically clean and controlled, so yeah... something's rong. It's 100% analog solid state, should be readily servicable, and worth reviving IMO.

    I can't find a PR 258 schematic, but I'll bet $0.37 USD that the amp is pretty much a rehoused Fender Bullet amp from the early 90s. Below is the clean channel preamp stage from a Bullet Reverb.
    Fender Bullet Reverb clean channel schematic.jpg
    Action items:
    1. Clean the channel switch S1 with contact cleaner.
    2. Clean the clean channel pot R13 with contact cleaner.
    3. Replace the C4 2.2 uF electrolytic capacitor.

    That electrolytic capacitor is at least 25 years old and is long past it's typical usable life. Electrolytics slowly consume themselves and go bad, causing any of various symptoms.

    While you're in there, replace the larger electrolytic caps in the power supply. Likely there are two.

    Items 1 through 3 are the likely suspects, plus replacing the 2 larger caps. If that doesn't fix it, it's off to the amp tech. If you can solder, and understand safety basics about working on amps, there's no reason you can't try fixing this for under $15.00 in parts.
     
    Last edited: Oct 14, 2021
  8. Anthonyraywright

    Anthonyraywright TDPRI Member

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    Thank you very much for the information, I'm going to get right on it. This is exactly the answer I was looking for I will keep you posted on the turnout.
     
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  9. NTC

    NTC Tele-Holic

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    That is why I asked how old it is - it sounds like the electrolytic caps have gone bad. Especially in the power supply.
     
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  10. archetype

    archetype Fiend of Leo's Ad Free Member

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    Yep. They're past their sell by date. :D I think they started making these amps in '93.

    Should replace the filter caps in the process, but it's probably that small one in the preamp, 'cause the problem is with the clean channel only.
     
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