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Fender PR 241 repair (Frontman amp made in Mexico, outputs a high pitched noise)

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  • Fender PR 241 repair (Frontman amp made in Mexico, outputs a high pitched noise)

    Hi to all!

    The above mentioned guitar amp was given to me for free. It is an old practice amp made by Fender in Mexico. Says model PR 241 on the sticker on the back and Frontman Amp on the front panel. It consumes 38 Watt and has an 8Ohm loudspeaker, so i suppose it outputs about 15 Watt RMS @8Ohm.
    I am trying to repair it (see below), so i can plug an 1x12" cabinet with a speaker like Jensen C12Q or Celestion Vintage 30. If it works OK, i am planning to throw away the factory 8" speaker and cut the amp in half so after modifying it, it will look like an amp head.

    The problem: amp turns on OK, it switches normally between clean and overdrive channel (i can hear the hum noise in OD) but it "screams" (see below) and outputs no audio from the guitar.
    When i plug a jack cable in the input, regardless of the guitar being connected or not, when volume is on zero it is quiet, but after trying to set volume at 1 or more then it starts sounding a high-pitched, constant, clear and very loud sound/noise (like a squeal or whine). It is so loud that my head buzzes and my my ears hurt even after i turn it of. My dog gets very stressed from this noise/sound. The sound changes pitch with treble equalizer knob, but other than that it is always stable on max db not dependent on the volume setting, and stops when i set volume to zero (volume/gain in OD mode) or unplug the input jack. With the guitar connected or not, it does the same thing whenever i have a jack plugged in the input of the amp. It does not change if i ground or short circuit the contacts on the other end of the cable, or if i connect and play the guitar. Already tested different good cables and guitars.

    Any ideas?
    Where should i start for troubleshooting?
    I have a (good) multimeter and some basic skills on desoldering and soldering. I know Physics well too, but i have little practical electronic repair skills.
    Also, if anyone could send me any schematics of the board, i would be grateful.
    If you need more photos of the amp or the circuit board, just ask for them and i will upload.

    Thanks in advance,
    Panos.

    P.S. Sorry for my poor/not-perfect English, i am from Greece.








  • #2
    I would first check for cracked/cold solder joints on the input jack itself.
    "Yeah, well, you know, that's just, like, your opinion, man."

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