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gutting audio amp

Discussion in 'Homebrew and Kit Projects' started by KB2WVO, Jul 7, 2018.

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  1. KB2WVO

    KB2WVO Ham Member QRZ Page

    ok i have a old midland 2m... yes midland 2m ...
    i got to thinking hey there is a audio amp chip in them there walls.. soooo i get the board out.. yep the preamp and amp are on one board that comes out.. sweeeetttt...
    will no.. becuse i dont know jack.. iam a bit lost here..

    images below.. audio in on main amp side it works. but no volume control.. i need to ask on adding that also..
    when i put audio in to preamp no go.. i put preamp audio on center pin on the left side of board. its in there but the audio output is next to nothing..

    i hate to rip the thing apart when it does work just need to tweak it up a bit hey lol
    anyways

    1 amp side audio in works no volume contorl ... yet need to add...
    2 preamp side center pin Ain no go.
    3 the amp buzz when u unplug the geetar ... that type of sound from speaker and even when i just hook wire to center plug that is hooked tonothing else..

    main amp chip TA7204p
    preamp chip TA7063p

    iam lost.. anyone have a map .. lol

    ty
     

    Attached Files:

    Last edited: Jul 7, 2018
  2. VK4FFAB

    VK4FFAB Subscriber QRZ Page

    Start by checking you have voltage on pin 7 of the preamp IC and collector of Q201, you have voltage on the base of Q201, and a drop in voltage to the emitter, check to see if C210 is ok and then Q201 is amplifying. Check C204 is fine and after all that its probably the IC which is dead.
     
  3. KB2WVO

    KB2WVO Ham Member QRZ Page

    red = 0.95 v
    blue = same as IC pin volts 8 volts.
    green = 0.32v

    C210 seems ok..

    also it was a working board from radio.. radio did work. just sooooooo old ..

    anyway to trace ? with sillyscope on the preamp chip ? if i inject a tone on input of preamp to trace it out ?
    and am i right to think.. D202 from pre to main amp side is the signal carry ?

    also am i puttin the audio in the preamp the right way.. iam guesing by tracing back to plug its center pin on the 3 pin plug where is pin 1 is power and pin 3 is ground.. preamp side
     

    Attached Files:

  4. KB2WVO

    KB2WVO Ham Member QRZ Page

    ok i injected signal on pin 3 of plug... that goes to pin 2 on chip. to the chip same input sine wave.
    from pin 6 i think is output of preamp chip . the sinewave is gone and its very very dirty sawtooth mix with trangel type singal .. its dirty...
     
  5. KB2WVO

    KB2WVO Ham Member QRZ Page

    the nice sine is from pin plug then to pin 2. reading taken at pin 2 on chip
    the wonkers sine is output pin6. all the way to D202 that goes to amp side
    settings on sillyscope not changed. 0.2v by 0.5msec
     

    Attached Files:

  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    What's the model number of the Midland?
     
  7. KB2WVO

    KB2WVO Ham Member QRZ Page

    13-510 2m fm .
     

    Attached Files:

  8. KB2WVO

    KB2WVO Ham Member QRZ Page

    this isnt a repair of the baord for radio..
    this is me takin the amp out to use for a bench speaker amp or project amp. i figured what the hay. its half done for me lol ..
     
  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    What you showed as "Audio in works" in your marked up schematic is not an audio input point. It's audio output tap from the preamp stage.

    The audio IN is at the far left hand side of the schematic. The TA7204P is only a 4W output amplifier, not good for "much," but have fun!

    Midland 13-510 AF Unit.PNG
     
  10. KB2WVO

    KB2WVO Ham Member QRZ Page

    so your sayin the redline i put in this image... is what needs to be there ??
    so where would the audio in be then ?
    ok iam lost.. lol
     

    Attached Files:

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