Marantz 2270 Power Amplifier Board Parts BOM

Discussion in 'Marantz Audio' started by PhilInAudio, Sep 10, 2017.

  1. PhilInAudio

    PhilInAudio Member

    Messages:
    54
    Here is some data that some of you may find helpful, especially when trouble shooting a board. Below is the voltage-across-resistors data that I measured from my properly functioning right channel Power Amplifier Board (P750) prior to the new parts being installed.

    Marantz 2270_PowerAmpBoard_VoltageAtResistors_Pt1_091017_01.jpg

    Marantz 2270_PowerAmpBoard_VoltageAtResistors_Pt2_091017_01.jpg

    I hope this helps.

    Phil
     
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  2. catrafter

    catrafter Marantz Specialist Subscriber

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  3. PhilInAudio

    PhilInAudio Member

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    54
    Tom thanks for the idea. I did buy the OnSemi MJE243G for H760, but haven't installed it yet given the notes on my BOM. Perhaps I should have read my note again. LOL

    OK...I'll install it and see what happens. I'll try to do it this weekend.

    By the way, I have jumpers on R784 and R785. The Service Manual calls for 3.9 Ohm resistors to be used in these locations. Why are jumpers used there instead?

    After listening to my 2270 for an extended period of time, as of right now, I really love the sound of my 2270!!! I still love the 250M, but the 2270 is just as wonderful! I have owned a lot of great stereo gear in my time, but there is something about the Marantz sound that I just can't put my finger on...it just blows me away! :)

    Again...thanks for the idea and please share any thoughts that you have on the jumpers question.

    Phil
     
    Last edited: Sep 22, 2017
  4. catrafter

    catrafter Marantz Specialist Subscriber

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    I'm glad you are enjoying your Marantz gear.
    The resistors in R784 and R785 can be used to control the output bias current. With jumpers in place (zero Ohms resistance) the bias current will be highest.
    Not in your case, but if the bias current is too high you could add resistors to decrease the bias current.
    Ecluser's case study in this thread covers most everything one needs to know about 2270 power amp bias.

    Tom
     
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  5. PhilInAudio

    PhilInAudio Member

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    54
    Tom...thanks for your response.

    I have studied Ecluser's case study on biasing the 2270 Power Amp Board (P750). What a fantastic explanation! What caught my attention was the 1,257 mV test point between each of the bases of H758 and H759. This is a fast and easy test point to check and it should render some good insight as to why my bias current is so low. (I'm getting 0.00 mV between J754 and J756 instead of the 5.0 mV specified by the Service Manual.)

    I also understand your point about the jumpers at, R784 and R785, that came stock with my 2270. Clearly if resistance is added at these points, the voltage generated from the current passing through the resistors would start to reverse bias the emitter junctions of the transistors, which, as a result, would decrease the bias current. So, in short, adding resistance at R784 and R785 is only good if you need to decrease the bias current. My problem is that I need to increase the bias current so changing the jumpers to any level of resistance would work completely against what I am trying to achieve! Tom, thanks for clarifying this.

    I'm still planning on changing out H760 and putting in the brand new OnSemi MJE243G part as you suggested and...if necessary, tinkering with the bias circuit resistance values. Unfortunately, I couldn't do it this weekend. I'll try to get to it tomorrow or Tuesday.

    I'll post the results.

    Phil
     
    Last edited: Sep 25, 2017
  6. PhilInAudio

    PhilInAudio Member

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    54
    OK..I have time this weekend to work on the 2270's bias issue in the left channel. I'll update everyone shortly.
     

     

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  7. Aaron99

    Aaron99 AK Subscriber Subscriber

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    Update?
     
  8. Steven Tate

    Steven Tate AK Subscriber Subscriber

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    Just wanted to make sure you had noticed the test points in the SM are only correct for very early units. For most 2270’s, measure bias between J754 and J760 and adjust to 10mV. This is discussed a couple of times in the Marantz Service Manual error thread.
     
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  9. PhilInAudio

    PhilInAudio Member

    Messages:
    54
    Sorry, I've been extremely busy for the past year and have been out of touch. Steven Tate...thanks for your last message! I'll recheck my 2270 when I get the chance. The good news is that my 2270 has been running absolutely perfectly since the amplifier section rebuild back at the end of 2017. I would say that the parts identified in my BOM worked perfectly well and I would highly recommend them for any 2270 rebuilding project.
     

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