Replace Transistor Question

Discussion in 'Pioneer Audio' started by BWareLOUD, Jun 15, 2017.

  1. BWareLOUD

    BWareLOUD New Member

    Messages:
    2
    Hi there, refurbishing a Pioneer SA-7500 with intermittent relay.

    For substitute transistors, can I used higher rated Voltage. (Such as is the case for capacitors - higher V can be used as substitutes as long as uF is met.)
     
  2. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    20,627
    Location:
    Bensenville,Illinois
    Deceptively simple question. Fraught with future danger. I can infer a lot from the question.

    answer: sort of. speed is important, and collector to base capacitance can tame things some, but...

    you have a lot of problematic transistors in the unit. 2sa725, 2sa726 and 2sc14151

    being new, have you lurked enough to have found the voluminous parts lists? have you read this forum much?

    it isn't enie menie minie moe, Pioneer even compromised in places and a DOUBLE compromise without reverse engineering the circuit to figure out what's important can result in problems when choosing substitutes...

    find the parts lists, familiarize with format, make your own list, basing list of what's in the BOM.
    then I will find similar circuits in other models with similar characteristics that I have already reverse engineered
    and modify the list with their subs.
    I don't have enough time to make the initial list, do the research and make substitutions.

    here's a teaser,
    AWM-072

    q5 2sc869 > 512-KSC1845FTA
    q6 2sc869 > 512-KSC1845FTA
    q7 2sc945 > 512-KSC1845FTA
    q8 2sc945 > 512-KSC1845FTA
    q9 2sa733 > 512-KSA992FBU
    q10 2sc945 > 512-KSC2383YTA
    q11 2sc1384 > 512-KSC2690AYS

    2sa725 > 512-KSA992FBU
    2sa726 > 512-KSA992FBU

    2sc1451 > 512-KSC3503DS
    2sc1312 > 512-KSC1845FTA
    2sc1313 > 512-KSC1845FTA

    I see no problems across the sa-7500 substitutions above.
    I don't have the power supply stuff yet.
     
  3. BWareLOUD

    BWareLOUD New Member

    Messages:
    2
    Thank you very much for your response,

    I am led to believe the issue is with a transistor in the power supply circuit causing the relay to not kick in. Does that sound accurate?

    I have got a service manual for the 7500, which I have used to identify original transistor models. I dont quite understand how to go about finding the replacements, nothing seems to match exactly on digikey etc.
     
  4. rcs16

    rcs16 Super Member

    Messages:
    2,901
    Location:
    Baldwin, Ontario, Canada
    Maybe, if the power supply voltages are not correct. Could be something else as well. Measure them and post your results, if you need assistance as to possible suspects.
    512-KSC1845FTA is a Mouser part number, so just search Digi-Key for KSC1845FTA and you come up with KSC1845FTACT-ND
    BTW, there is a direct sub for NEC 2sc945, Fairchild ksc945c, which is 100mA Ic rated vs ksc1845 50mA rated. Depending on the place used, a ksc1845 can be used if that is what you have on had.
     

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