My first receiver restoration attempt: G-6700.

Discussion in 'Exclusively Sansui' started by ghazzer, Nov 12, 2012.

  1. ghazzer

    ghazzer Sansui addict Subscriber

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    2,666
    Location:
    Sykesville, MD
    Updated 9/11/2014

    I finally found one, but not in the condition I wanted - It won’t power up!

    The price was acceptable, and now I have a good project for the winter. Arrival pics and nudies can be seen here:

    http://s1110.photobucket.com/albums/h453/ghazzer/Sansui G-6700/Arrival/

    The 7A main fuse is blown and the right (not left) channel output transistors are (not open) shorted. They are also NTE replacements, so someone has been in here before. I won’t be able to tell much more until I can get my workbench cleared and get set up for this one. I got started by searching AK for related threads and ran slam into a 27 page thread by Andreslober about his G-7500 – they both have the same main board & drivers. Kevzep & Overundr1 spent nearly 4 months helping him troubleshoot his Sansui and there is a wealth of good info there. Now I need to go back and re-read it all.

    I won’t be working on this every day, so my restoration may last longer. ‘Hope I enjoy it and learn a little. The first thing I have been reminded of is to watch out for counterfeit parts!

    Constructive comments and suggestions are welcome. I'll need all the help I can get - - -
    .
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    Location of photos or images:

    "X-Ray" of F-2980 board..... - pg 2 / post #27
    Corrected Bias schematic.... - pg 5 / post # 84
    New jumper pins................ - pg 5 / post # 89
    Re-drawn Driver Circuits..... - pg 5 / post # 95
    Etched F-3058 replacements - pg 9 / post # 162
    Tracks of F-2853 board....... - pg 12 / post # 231
     
    Last edited: Dec 22, 2016
  2. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Would not be the Sansui forum without a Gx700 rebuild to chew on. Get the dmm and soldering iron ready Steve, several of us enjoy the challange.
    Btw once up and running they sound really good.
    Lee
     
  3. Overundr1

    Overundr1 AK Subscriber Subscriber

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    You will need a dim bulb tester as well.
     
  4. gold01ca

    gold01ca Active Member

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    Cranbrook BC Canada
    your pics link doesn't seem to work.
    look forward to following your progress,
    good luck!
     
  5. kevzep

    kevzep Its all about the Music Subscriber

    I am in on this one.....:thmbsp:

    You say the output transistors were "open", that is not a normal way for transistors to let go, they almost always short out....

    How were you measuring them? Did you take them out to measure?
     
  6. 1979

    1979 New Member

    Messages:
    43
    Hi,

    Can you recheck the link you mentioned that has the pics? seems like it doesnt work....
     
  7. ghazzer

    ghazzer Sansui addict Subscriber

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    Location:
    Sykesville, MD
    The link to the pics has been fixed.

    I just spent about 45 minutes answering questions and telling you what I have done so far, and plan to do, when POOOOF: Photobucket crashed and caused all my iexplorer windows to reset.

    Gonna crash now & try to re-construct it tomorrow (in WORD).
    .
     
  8. ghazzer

    ghazzer Sansui addict Subscriber

    Messages:
    2,666
    Location:
    Sykesville, MD
    Getting parts during this process will be time consuming, and the Scots-Irish part of me rebels at paying S&H for each piece. My plans are to do a resistive map of the left channel driver circuits and compare it to the right channel, and plot out any failed components. Then I can order all of the replacement parts that are needed, at the same time.

    I have ordered 2 pair of Sanken OP TRs (hope they are not counterfeit), and a set of 100Ω, 5W ceramic cement resistors for powered up testing later.
    I need to order Mica washers and thermal grease, unless the grease I have for mounting CPU chips in a computer will work here. (???)

    I have the parts for a DBT and will build one based on the excellent thread by Overload.
    http://www.audiokarma.org/forums/showthread.php?t=465423

    One of my first lessons learned will be to trust my notes, NOT my memory. The OP TRs were not open. You were right Kev!

    All references in this thread will be to the LEFT channel, and “in circuit” unless noted otherwise.
    TR 601 NTE36 LF102G: B-E = 94Ω/94Ω; B-C = 94Ω/94Ω; E-C = 0.0Ω/0.0Ω
    TR 604 NTE37 LF102M: B-E = 0.0Ω/0.0Ω; B-C = 0.0Ω/0.0Ω; E-C = 0.0Ω/0.0Ω i.e. = shorted


    [​IMG]

    Seems like I am getting nowhere with my efforts to track down the BUM HUM in my CNC phono preamp. May have to move that aside and put this “mua-tha” on the bench and get started.
    .
     
  9. kevzep

    kevzep Its all about the Music Subscriber

    They are both shorted, toast, finished.......:thmbsp:

    When you get the new transistors we will do some Ω measurements on them, and we might be able to prove them to be the real thing....

    Also bear in mind, although its good to test the driver boards as you have planned, often semiconductors will look OK on a DMM but when in circuit under load, can break down.....

    Well, we're off to a good start......
     
  10. ghazzer

    ghazzer Sansui addict Subscriber

    Messages:
    2,666
    Location:
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    BTW, here are the comparable values for the RIGHT channel:
    TR 601 Sanken A1106N 98Y: B-E = 226Ω/226Ω; B-C = 21KΩ/24KΩ; E-C = 21KΩ/24KΩ
    TR 604 Sanken C2581N 98Y: B-E = 226Ω/226Ω; B-C = 21KΩ/23KΩ; E-C = 20.5KΩ/23.5KΩ

    If the “98Y” is a date code, it means that these are not original.

    I'm thinking that it is wise to replace all 4, at this time.
    .
     
  11. nosirrah

    nosirrah Moderator Moderator

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    In the pics I see NTE semiconductors, not recommended.
     
  12. kevzep

    kevzep Its all about the Music Subscriber

    Those NTE's are toast anyway Casey, he has some Sankens on the way (hopefully not counterfeit.)
     
  13. OverLoad

    OverLoad High On Solder Fumes

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    It's the lot# and hFE rank; nothing to do with a date code.
     
  14. ghazzer

    ghazzer Sansui addict Subscriber

    Messages:
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    Location:
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    Based on the research I have done so far, here are the (available) replacements I have identified. I am avioding fleabay except for the 2 pair of Sankens I have already ordered.

    type...Designator............Original..........Replacement
    NPN....TR01-4................2SC1845........KSC1845
    PNP....TR05-8,19,20….....2SA939..........KSA1220A
    NPN....TR09&10.............2SC2071........2SC2258
    NPN....TR15&16.............2SC2238........MJE15032
    PNP....TR17&18.............2SA968..........KSA1381
    - - -
    NPN....TR601(2ea).........2SC2581.........NJW3281G*
    PNP....TR604(2ea).........2SA1106.........NJW1302G*


    * To be used if the Sankens don't pan out.
    .
     
  15. OverLoad

    OverLoad High On Solder Fumes

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    Looks like you got some misinformation during your research.
     
  16. ghazzer

    ghazzer Sansui addict Subscriber

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    Location:
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    Thanks for the feedback. I am continuing to re-evaluate the options. There are some enticing offers on fleabay, but mostly from China and I am very leary of counterfeit parts.

    The scribbled notes are piling up and it is getting tuff to keep track of the numbers. 939 & 968 are getting transposed. Some of these choices are driven by what is available at Digikey or Mouser. Some of the damn things ARE available, but the MOQ is 2,000 or more!

    One main thing I need to do is to read up on the criteria of what defines a "suitable sub" for a transistor, and which parameters are more important. I suspect that the criticality of the parameter may vary with the role that a TR plays in a circuit.

    Mind boggling - - -
     
  17. OverLoad

    OverLoad High On Solder Fumes

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    Every single one of the subs are readily available from Mouser with no minimum quantity or order.
     
  18. ghazzer

    ghazzer Sansui addict Subscriber

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    I could not find the 2SC2258 at Mouser, and would like to get some more info on the MJE340 before settling for that. 1W vs 20W, and I cannot find Ft.

    2SC2258 is 63¢ at Digikey, but KSC1845 & KSA1381 are shown with large MOQs. I'll have to call them.
    .
     
  19. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Do try to avoid fleabay /China as the source for your replacements.

    There is very often, although getting more difficult now, an equivalent which will fulfil all the roles of the original. Those recommended by the experts, Overload / kevzep / avionic et al, are the ones to go for.
     
    Last edited: Nov 16, 2012
  20. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    No they aren't - you can buy any quantity from 1 upwards. (Mouser)
     

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