Anyone into Guitar Amplifier repair?

Discussion in 'General Electronics Chat' started by SkidPlate, Jun 15, 2009.

  1. SkidPlate

    Thread Starter New Member

    Jun 1, 2009
    6
    0
    I am somewhat of a newbie and need some help with my Marshall Amp model 8240.

    The Problem, My amp makes a buzzing noise when I pluck a note it starts out quiet then comes up to volume with a lot of buzz or distortion. I have done some reading around other forums and read problems similar to mine are capacitor related.

    I pulled my amp apart and browsed over all of the capacitors and found one with some dry gunk coming from the bottom of it. I looked at the schematic and I can't make heads or tales from it. I was hoping someone here might be able to help me if they take a look at the schematic.

    I am waiting on a new to me fluke 87V should be here this week then I will pull and test said capacitor to verify it's condition.

    Schematic http://www.drtube.com/schematics/marshall/8240-61.gif
    The capacitor is C34 it is located near the top right corner and to the left of where it says transformer no. T5968. Could C34 make the problem that the amp has?

    Any help is greatly appreciated.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    It could be that the capacitor gives the problems.
    When this capacitor is bad it can lead to a loud hum.
    Can you post a picture of the stuff getting out of the capacitor?

    Greetings,
    Bertus
     
  3. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Replace the cap. If you are sure it's not just glue you see, don't even think about it.
     
  4. callbo

    New Member

    Aug 15, 2009
    1
    0
    the cap you are refering to is a filter cap in the power supply section of the amplifier. Its job is to remove noise in the power provided to the rest of the amp. Yes it will definitely cause the problem you describe. The substance you are refering to is probably oil since it is an electrolytic capacitor and oil is common as a component of these type of caps. If you replace it you must observe polarity. This means there is a positive and a negative side to the cap. the positive is marked with a + sign and the negative with a - . sometimes only the negative will be marked. Pay attention to the markings on the cap when you remove the old one and only replace it with the same type and rating. Yours is a 47uf 350 volt cap. Most likely a radial lead. Check all the caps in the amp in this (especially in this area) for swelling or leakage. If you don't have any experience with electronics component replacement then I suggest you take it to someone who can do the work for you. I am a electronics technician with 35 years in the field and have seen this type of problem often in high voltage video and audio circuits.
     
    Last edited: Aug 15, 2009
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