HELP a brother out! I need some advice on how to fix my Marantz Model 18 scope.

Discussion in 'Marantz Audio' started by PooPoo, Nov 14, 2017 at 2:41 PM.

  1. PooPoo

    PooPoo Member

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    Just replaced the 4 transistors with replacements C2611 that were mounted on the heat sink on the scope board. Another member told me the pinout were the same as the originals but still no scope??? The crt tube has a glow on the bottom but won't turn on.??? Anyone might know where I should fix? image.jpg
     
  2. eiraved

    eiraved AK Subscriber Subscriber

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  3. PooPoo

    PooPoo Member

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  4. eiraved

    eiraved AK Subscriber Subscriber

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    There's no magic solution on my part. It's gonna take some work on your part though...have you checked for the voltages at Q1201 - Q1206 per the schematic?
     
  5. PooPoo

    PooPoo Member

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    Q1201,1204 are 34-1030 fets how do you test those with a DMM ?
     
  6. ausman1000

    ausman1000 AK Subscriber Subscriber

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    Your C2611's are not installed correctly. The pin out is the same as the originals. After removal check them with a tester, they may have been damaged.
     
  7. ausman1000

    ausman1000 AK Subscriber Subscriber

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    NPN not FET
     
  8. eiraved

    eiraved AK Subscriber Subscriber

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    Check this out first before you entertain my ideas.
     
  9. PooPoo

    PooPoo Member

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    They checked out fine still. So how are we suppose to install these? Do I need to flip them? image.jpg Thought this is how the originals were mounted?
     
  10. PooPoo

    PooPoo Member

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    Do you have a picture of how you installed your c2611?
     
  11. eiraved

    eiraved AK Subscriber Subscriber

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    I'm guessing those two black dots near the center of the board are Q1201 and Q1204. Aren't there visible legs coming out of those which attach them to the board?
    You can come back to those later. For now, check the voltages on Q1202, Q1203, Q1205, Q1206 trannies for proper readings per the Marantz Service manual pg. 26, fig. 23. Please post the readings.
     
  12. PooPoo

    PooPoo Member

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    image.jpg
    Are these C2611 installed the correct way? Or do they need to be flipped and mounted underneath the heat sink?
     
  13. eiraved

    eiraved AK Subscriber Subscriber

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    The pinouts of C2611 as they are mounted on the board in your photo are ECB from right to left. I don't know the pinouts of the original transistors and the schematic doesn't show the pinouts either.

    I did read in another post that the TIP47 transistor can also be used as a substitute for the 34-1006. If the TIP47 is mounted on the heatsink similar to how you mounted the C2611, the pinout would be BCE from right to left. Just flipping the C2611 on the heatsink (they don't have to go under) would give you the BCE pinout.
    EDIT: I studied the schematic some more and it appears the pinout should be B on the right, C in the center and E on the left using the photo view given. So it appears you currently have it reversed.

    @bktheking also has some knowledge on the Model 18. Maybe he can pitch in with some well needed advice.
     
    Last edited: Nov 15, 2017 at 9:31 AM
  14. bktheking

    bktheking Gitter Done!

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    You have your transistors reversed- the pattern looking from the front left hole to right is ECB, you have your transistors installed BCE- flip em. Make sure you put thermal grease on the bottom with the round insulators and screw them down to the heatsink.
     
  15. bktheking

    bktheking Gitter Done!

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  16. Omegaman

    Omegaman Ultra Super Member Subscriber

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    Look at the pictures you took before the work was done, that should reveal the flaw
     
  17. PooPoo

    PooPoo Member

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  18. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    If you mount them like this (without insulator around the screws) you will have a short between collector and heatsink . I would not recommend it ! usually main voltage is on collector and mounting them this way be the same than put your + and - to ground !
    If I had to refix this board , I will flip them , put the good side of the transistor on mica and fixed them with a screw without insulator's screw . Then I will use wire to connect each transistor with the right point on PCB ;
    Easy
     
  19. bktheking

    bktheking Gitter Done!

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    You will need those round mica insulators between the screw and the metal part of the transistor back like clinic-audio says. Sorry I should have explained that better- i didn't think it was live as the hitachi pfd doesn't say it is which means there were variations in manufacturing- i guess some have a case collector and some don't- guessing these aren't hitachi ones.


    http://www.svntc.com/TPDF/2120.pdf

    Collector connected to mounting base.
     
  20. eiraved

    eiraved AK Subscriber Subscriber

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    Just check for continuity between the metal plate and the collector pin. No continuity means they are not attached, so an insulator would not be needed. However, the metal plate is there to better dissipate heat from the transistor to the heat sink, so it should be facing the heat sink.
     

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