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Fender princeston 112 Plus Distorted clean channel

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  • Fender princeston 112 Plus Distorted clean channel

    Hi All

    I posted a thread on here about a week ago about this amp . friend said the vol on clean channel was either on or off

    Anyway i checked it out and it was and fitted a audio taper 50k which seem to of done the trick

    I noticed when i was testing it that the clean channel was like the overdrive channel distorted
    while testing it further the TIP142/147 blow. Ive replaced them and it back working again. but still distorted
    Supply voltages are correct + 42v and - 42v

    Using the signal gen and scope ive found the signal going output stage area is correct, ( C34 ) But at pin 3 it don't look right

    http://elektrotanya.com/fender_princ.../download.html

    Click image for larger version

Name:	SAM_1084.JPG
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ID:	867590 at C34

    Click image for larger version

Name:	SAM_1085.JPG
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Size:	2.13 MB
ID:	867592 at pin 3 of mc1436p1

    Click image for larger version

Name:	SAM_1086.JPG
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Size:	2.26 MB
ID:	867593 at pin 6

    Click image for larger version

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Size:	2.27 MB
ID:	867594 at the output to dummy load

    I may be wrong but it looks like the Mc1436p1 is faulty. Can anyone help

    Bassman
    Last edited by blindboybenton; 08-26-2013, 03:25 PM.

  • #2
    On the output to dummy load, is that baseline at zero volts or is it elevated DC? The output of the IC looks like half a sine wave, but the amp output looks more like just peaks.

    If you had blown outputs, then check the 0.47 ohm ballast resistors for opens, check all eight diodes between the bases of the outputs.

    You may have +/-40v. but to you have +/-25v at the IC itself?
    Education is what you're left with after you have forgotten what you have learned.

    Comment


    • #3
      Thank you Enzo

      Ive just checked and one of the 0.47R is high. I will change it in the morning. I'm learning slowly. Ill let you know the outcome

      Bassman1965

      Comment


      • #4
        And if you are not familiar with that type of amp from Fender, do not run the amp without having the output devices correctly heatsinked or they will overheat and short out.

        Comment

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