Sansui G-7500 no power/sound with burnt resistor on F2890 board

Discussion in 'Exclusively Sansui' started by dsmart705, Feb 10, 2019.

  1. dsmart705

    dsmart705 New Member

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    4
    Hello,
    I have a G7500 that is in need of help. The unit will not power up or produce any sound (meter lights still turns on and the tuner appears to be working) so I pulled off the cover and after blowing out 40 years of dust I gave it a quick visual inspection. There is alot of brown goo stuff around the cluster of caps near the relay. It almost looks like the glue has corroded some of the resistors/caps and wiring in that area. Im not sure if that was what did my amp in or its just superficial but my intent is to clean it all off. The resistor that is burnt and R36 and is charred beyond being able to tell what colour bands it has but it looks to start with orange and end with gold. R78 which is one of the 5w.33ohm resistors is open circuit but the other 3 are testing good. The board itself appears to be unharmed. I cant see anything else that looks bad but havent metered out everything on that board yet.

    from my research repairing this particular board may be over my head but I would like to give it a try. Ive tried to track down the parts I need but have not come up with anything solid. I was hoping for some guidance on the repair or if someone feel like a challenge I could always send out the board. Thanks

    David
     
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  2. Tom B

    Tom B AK Subscriber Subscriber

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    If you have an open emitter resistor, then you probably have bad output transistors, as well as bad parts on the amp board like resistors and driver or other transistors in that channel.
     
  3. Super Noob

    Super Noob AK Subscriber Subscriber

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    The schematic and service manual are at HiFi Engine.
     
  4. dsmart705

    dsmart705 New Member

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    Thanks for the replies. I did have a look at the schematic so im starting to build a parts list. I cant seem to find any reference to the type of resistor R36 is. Its not mentioned in the parts list. Is there a standard "replace while in their list" regardless of what my specific issue it. From what ive been reading it seems like people are doing the

    1. Bias trimmers - VR01, VR02, VR03, VR04 replacement type ?
    2. Output transistors - TR601, T602, TR603, TR604 (confused with these as there are some on the F2980 board and the same ones listed for the F2981 boards) replacement type?
    3. Emitter resistors....that's an easy one
    4. Capacitors (dont really want to shotgun replace those things if its not neccessary to get it running)

    My amp has all the fuses intact, I have read through alot of threads on the matter but cant really come up with a definite parts list for the stuff I need. My experience with the components is fairly limited so excuse my ignorance. I have an interest in this sort of thing and want to "get my feet wet" and gain some experience which is why this project is happening.
     
  5. Tom B

    Tom B AK Subscriber Subscriber

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    Sansui doesn't list all the resistors in the parts list, but does show them on the schematic. R36 is a 150 ohm 1/4 watt resistor
    I would suspect TR08, TR10, TR16, TR18, and the 2 outputs TR601, and TR602.
    Also check R44 which is a 220 ohm 1/2W resistor, R38 10 ohm 1/2W resistor and the trim pot VR04 to make sure they aren't open. You should also check the Bias diode STV3 which is mounted usually on the heat sink, or on one of the driver heatsinks. Those diodes can short or open. (they are 3 diodes in series internal)
     
  6. jd3rdcoast

    jd3rdcoast AK Subscriber Subscriber

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  7. dsmart705

    dsmart705 New Member

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    Thanks so much for the guidance,I know im in over my head with this but honestly its not worth it to me to pay $400/500 to have this thing rebuilt..there is nobody in my area who is still doing this type of thing and the shipping alone would be a killer. You were right about R44 and R38....they were both open. I also found R54 was open. so far my list is

    All 4 emitter resistors, TR601/602 output transistors for both channels, R36/38/44/54, All 4 trimpots (no sure what part to get yet), TR08/10/16/18.

    Part numbers ive seen so far taken from actual component are. Hopefully they are all available or there are compatible replacements.

    Emitter resistors x 4 - 0.33K Ohm 5w

    R36 - 150 ohm 1/4w
    R38 - 10 ohm 1/2w
    R44 - 220 ohm 1/2w
    R54 - 220 ohm 1/2w

    Left Channel
    TR601 - C2581N 02Y
    TR602 - A1106 020
    Right Channel
    TR601 - A1106N 8DY
    TR602 - C2581N 8NY

    TR08 - A939 V
    TR10 - C2071 V
    TR16 - NEC D381 2M7YC
    TR18 - NEC B536 2M8IC

    VR01 - 8D5d 100ohm B
    VR02 - 8D5d 100ohm B
    VR03 - 8D5d 100ohm B
    VR04 - 8D5d 100ohm B
     
  8. dsmart705

    dsmart705 New Member

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    4
    Well I went ahead and ordered everything (doubles of some just incase). Managed to find all the parts using the help of others who have gone down the same path. Also ordered some of the capacitors that are in the brown goo area and may have been damaged. I will report back once I have everything replaced and will no doubt have more questions about setting the trimmer/bias pots and how to setup the amp. Thanks for all the help
     
  9. Super Noob

    Super Noob AK Subscriber Subscriber

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    326
    Location:
    Fort Myers, FL
    Good luck... my rebuild on my working unit went well. I assembled a cap list on the thread.

    http://audiokarma.org/forums/index.php?threads/sansui-g7500.835199/

    I love my G-7500.
     
  10. Tom B

    Tom B AK Subscriber Subscriber

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    Not sure if you know this but ebay is not a great source for transistors, especially outputs and drivers. There are many counterfeits being sold. It is usually better to get your transistors from a place like mouser. That being said, those original outputs and drivers are not being made anymore, so you probably need to get on-semi replacements.
     

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