Echolette ME IV

Discussion in 'General Electronics Chat' started by CornElvis, Oct 17, 2010.

  1. CornElvis

    Thread Starter New Member

    Oct 17, 2010
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    Hi everyone,

    I'm new to this forum and I'm not an engineer. I do know some basics and repaired guitars and amps, but this one amp is a pain....
    Here's the story. Two fuses blew up everytime you switched it on. I replaced 4 Resistors of 33Ω (R428 t/m R431 on the ME_IV_E_1_cir.PDF), they were totally burned out. Now the fuses stay OK, but there is terrible hum. If I take out R429, the hum is gone and there is sound, but very little and very sharp, not the way this amp should sound at all.
    The hum really sounds like there is direct current or broken ground somewhere. Now by checking the amp I found a loose cable as well, black (should be some kind of ground right with that color...) and this is connected to the 80160 board on the same schematic, I figured out that should be number three going to the left Connector C pin 7, but the weird thing is this is not the ground but the signal wire. I tried both btw and none of them take the hum away, not making any difference, but I want to know where to hook up this cable. the ones connected are two times yellow and two times red, leaving this black cable as the fifth.

    Can anyone make sense out of this and point me in the correct direction please?

    Very much appriciated.

    With kind regards,

    CornElvis
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    How is the condition of C510 and C511?
    Are they bulged or is there some stuff coming out?
    What is the voltage across them?

    Bertus
     
  3. CornElvis

    Thread Starter New Member

    Oct 17, 2010
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    Bertus thanks for the quick reply!
    I checked them and they are in mint condition, like new. The voltage is 36 V as indictated on the schematic.

    BTW. If I take off the Bass and Treble modules (84026), the hum stays.
     
    Last edited: Oct 17, 2010
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When you remove R429, the current limiting will start working and take away the power.

    Bertus
     
  5. CornElvis

    Thread Starter New Member

    Oct 17, 2010
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    I think I noticed that, but then the amp sounds like sh.. and too soft for what it should be.
    Anything else where I should look? That loose black wire (number 3 on 80160) ? I connected that to the place where it should be on the schematic, but hear no difference at all.

    Thanks for the help!
     
  6. CornElvis

    Thread Starter New Member

    Oct 17, 2010
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    no one? Just one bumb and then I leave it for what it is.... :)
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    No need to bump.
    There are also people who need to work.

    For line 3 in the schematic:
    That is part of the switch on delay.
    The speakers are switched on afther some delay time.
    As long as the speaker is not active line 3 is connected to ground to be sure there is no signal going out.

    Bertus
     
  8. CornElvis

    Thread Starter New Member

    Oct 17, 2010
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    OK thanks for that.
    And about the bump, you are right
     
  9. bertus

    Administrator

    Apr 5, 2008
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