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Panasonic Amplifier -- Transistor Replacement

Discussion in 'Troubleshooting and Repair' started by bonesy, Jun 9, 2010.

  1. bonesy


    Jun 9, 2010

    I am endeavoring on a project to replace a transistor in my Panasonic Amplifier. The system is making the "pop" sound after being on for some amount of time and does not require any inputs. Upon observation the circuit board around position Q5005 looks heat stressed by a black coating on the top side of the main circuit board. The transistor is stamped C3940AR and after searching the internet, one post suggested replacing the transistor with a TIP31C. I have a couple questions:

    Is the TIP31C a compatible replacement for the Panasonic C3940AR?

    I am in Wash, DC, and the only place that I know sells components is radio shack. On their website they have a TIP31 listed but do not provide the maximum power ratings. The poster suggest the version C which has a maximum power handling of V=100. If I were to use versions A or B, would they burn out or ruin the circuit board, or is the 100 power handling a precaution?

    Also, since it seems that this transistor (40W dissipation) burned out, would it be advisable to increase the power handling to a transistor with higher power handling such as the TIP120 (80 W) or the TIP42G (65 W)?

    I am least familiar with transistors so I wanted to ask for some advice before I proceeded. Thank you for any assistance that you may provide.
  2. Tesla


    May 10, 2010
    I can't really help with your specific transistor questions, but my guess would be if it's working for any amount of time, that part is ok.

    If you want to go about this like "it's broken and I would like to fix it" ... What model is it? How old is it? Is this transistor screwed or clamped to the main heatsink? Does it have a fan, and is it working?
  3. davenn

    davenn Moderator

    Sep 5, 2009
    and added to Tesla's valid quest for more info from you.....

    where in the circuit is it ? ..... in the power supply or an output transistor or somewhere else?

    a C3940AR transistor I would interpret as a 2SC3940AR which is a plastic cased TO92
    type Vceo of 50V and a Ic of 1Amp and 1W dissapation.... is the transistor you have a TO92 case ?
    Or is it a TO220 case .... flat plastic front and metal tab with a hole in it ??

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