1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

Shorted 6060

Discussion in 'Exclusively Sansui' started by rotco, Jun 14, 2018.

  1. rotco

    rotco Active Member

    Messages:
    157
    Hi everyone
    please, i need your help with this one.
    i will say first that i'm an amateur, but have basic knowledge and experience which i got mostly from you guys.

    i just done cleaning and maintaining Sansui 6060 which was work absolutely fine.
    as last step, i just wanted do to the Bias adjustment as described in the S.M
    Mistakenly, while touching the resistors leads with the DMM probes, i also touched the chassis and then the two fuses got burned. (F603, F602) (250V, 5A)
    1. While the fuses are off from the board, i turned on the receiver, it powered on, but the protection relay didn't "click".

    I hope tomorrow i will find new fuses in the store,
    but i really think that something went bad and the new fuses will auto-burned while i will turn the receiver ON.

    I have a Dim Bulb Tester, i will use it. if i will find the receiver is shorted, which test can i make in order to find which components got died?

    thanks

    B.T.W is there any chance that nothing got damaged and if i'll put new fuses the receiver will play again?
     

     

    Please register to disable this ad.

  2. Tom B

    Tom B AK Subscriber Subscriber

    Messages:
    1,471
    Location:
    Bay Ridge, Brooklyn New York
    While I would hope that all will be fine after replacing the fuses, in reality those 2 fuses are the ones supplying primary DC to the output transistors and driver board. They usually pop when output transistors short.
     
    slimecity likes this.
  3. rotco

    rotco Active Member

    Messages:
    157
    Unfurtunatly, i couldn't hold my self andwait to get new fuses, i was so curious if something went wrong or maybe everything just fine exept the fuses themselfs.

    So, i wrapped the fuses with aluminium foil, and powered ON the receiver thru a Dim Bulb Tester with 60W lamp in series. (My wall power system is 220v)

    It turned ON, but after about 10 seconds or less i notice a SMOKE! (I know i did stupid thing) and i turned it OFF immedietly.
    The smoke raised from the middle area of the vertical board (F-2647)
    I couldnt notice exactly where from, and couldnt notice burn smell from specific area or see a signs of black "burn" spot.

    I feel really lost..

    What do i need to do?
    Start by tacking off the output transistors and check them? If they are shorted, replace and hope that will solve the issue?
     
  4. Tom B

    Tom B AK Subscriber Subscriber

    Messages:
    1,471
    Location:
    Bay Ridge, Brooklyn New York
    Foil wrapping fuses, as you found, was the worst thing you could have done. You probably had shorted outputs, and now you may have a number of other components bad.
    I would suggest you find a good component level technician familiar with vintage gear to fix your unit.
     
    rotco, slimecity and Hyperion like this.
  5. rotco

    rotco Active Member

    Messages:
    157
    But!!
    I used a DBT!
    I thought it should protecting me!
    Limit the current... And in any case i have a short.. So.. What could have happen?
    The current will move thru the short and nothing bad will happen!
    Thst what i thought.. At least..
    My only suspect is.. That there was no short.. And while i used the aluminium foil.. Then i couse one to happen!
    But.. Again.. Why the DBT didnt saved me in that case?!
     
  6. rotco

    rotco Active Member

    Messages:
    157
    Hi guys

    i came back working on this receiver.
    i installed new 5A fuses and connect it thru DBT, i've got short (Light bulb was fully ON).
    so i disassemble the Driver circuit board (F-2647) and now i haven't got short (Light bulb was almost OFF)
    not sure if i can conclude from it that the culprit is in the F-2647 board ( i wish cause it's a simple board),
    but for some guess I mostly suspect the four (output) TO-3 transistors.

    i rather take measurements on live, rather than take them off the board and check them outside.
    maybe someone can help me determine the correct voltages on their leads to verify?

    or maybe you recommend to take them out and check if they are shorted?

    Thanks sansui 6060 F-2648 schematics.JPG sansui 6060 F-2648 diagram.JPG sansui 6060 output transistors.JPG
     

     

    Please register to disable this ad.

  7. rotco

    rotco Active Member

    Messages:
    157
    any help with it please?

    im looking for reference. i suspect the power transistors (TO-3) is bad.
    any one can give me a reference please? i thought of measuring the resistance (or diode test) across their leads on dead unit (power OFF)
    is it applicable?

    thanks
     
  8. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    48,131
    Location:
    Hertfordshire, UK
    Last edited: Sep 11, 2018
    rotco, Oldsansui441 and slimecity like this.
  9. rotco

    rotco Active Member

    Messages:
    157
    @Hyperion
    Thanks for your feedback!

    I just started to "play" a bit while power OFF, and measured resistance between the transistors legs.
    3 out of four seems different than 1 other.
    The 3 showed few mega ohms, while the other showed short (0.8ohm).
    Isn't it points on something?

    Assume i will check them and one of them is found dead.
    I will be need to replace all the 4?
    If so (or even only one or a pair)
    What should i do next?
    You saod there might be other driver transistors might be bad.
    Would it be possible to "deal with them later"?
    Or i have to check that prior to powering ON
    Since they might couse the new outputs to burn again?

    I have DBT to do some tests.

    There is no "static" measurements i can make on the driver board? (It's quite small)
    I thought maybe someone here can tell me what to check.
    Or, maybe i can get other orderly 6060 from a friend and do some comparissons.
    (I would rather not to switch boards or something couse i dont want to risk his receiver)

    Thanks
     
  10. kevzep

    kevzep Its all about the Music Subscriber

    You've blown some of the output transistors, you need you replace them, this is what the short circuit is...
    You will need to check the driver transistors and replace if necessary as well.
     
    rotco and slimecity like this.
  11. rotco

    rotco Active Member

    Messages:
    157
    who are the driver transistors in this 6060 Sansui?

    i thought i batter order all the perspective components and just replace them.
    because, if i replace only the output transistors, they probably will burn again? (they are the most expensive components here and i dont want to risk burning them again. thay are 5.5*4 +8 shipping. about 30usd.
    is there any "list" of recomneded components should i buy?

    thanks
     

     

    Please register to disable this ad.

  12. rotco

    rotco Active Member

    Messages:
    157
    also @Hyperion

    on board F-2648 power supply:
    Two transistors:
    TR06, TR05. (2sc711). (lying on back, with thermal paste attached to the big heat sink)
    Two transistors:
    TR604, TR605 (2sd313). (mounted each on single small heat sink)

    on board F-2647 driver board:
    5 for each channel:
    TR01, TR03 (2SA726)
    TR05 (2SC1951)
    TR07 (2SD438)
    TR09 (2SB560)
     
  13. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    48,131
    Location:
    Hertfordshire, UK
    These are TR07 & TR09, and TR08 & TR10, according to the schematic they are 2SD438 (07, 08) and 2SB560 (09,10) respectively.

    2SD438 are obsolete so the nearest modern equivalent will be KSC2316
    2SB560 are also obsolete so nearest modern equivalent will be KSA916
     
    rotco likes this.
  14. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    48,131
    Location:
    Hertfordshire, UK
    Bias transistors - note there are 2 x TR05 and 2 x TR06 labelled on the schematic - they should have unique numbers the 'other' TR05 & TR06 are pre-driver transistors
    Power supply regulator transistors
    Differential input pairs
    pre-driver transistor
    driver transistors - as previously posted.
     
    rotco likes this.
  15. rotco

    rotco Active Member

    Messages:
    157
    Hugggee thanks!
    Now that im familiar with the terminology, and begin to "understand" the role of each transistor by it's name.

    After i'll change the output transistors.
    May i power ON thru DBT 60W 230V?
    will it keep the output transiator safe in case there other component that went bad?

    Or any precautions that i shuld do?

    is there any of the other tranaistors that i better replace also incidentally the output transistors?

    Ive read somewhere that maybe the bias trimmers (vr01, vr02) might be "over the setpoint" and might burn the output transistors again.
    Is there anything i can do to make sure its in "safe value"?
     
  16. rotco

    rotco Active Member

    Messages:
    157
    I measured on board (no power)
    I got a short in 1 of the output transistors (0.9 ohm) pins base/emitter.
    So, 100% this is shorted and no need to take it off board to determine that. (Correct?)
    This one is TR01 NPN left channel.

    I compare it to the equivalet TR02 NPN right channel and they behave different.

    I wanted to do more references, found thst all the big white (cement) resistors are the same 0.5ohm
    (R05-R08)
    (s.m parts list says 0.33ohm 2W)

    But, the fusible resistor r01 (related to the shorted transistor TR01) is also behave different then the 3 others.
    The others are 6.9 ohm
    But r01 is 7.1 ohm.
    (s.m parts list says 6.8 ohm 0.25W)


    Is it bad?
    Or maybe its just different because of the shorted TR01?
    If i will need to replace it.. Again.. Do i need to replace all of the 4 resistors?

    Thanks

    ** all measurments did on board without power.
    Resistace of DMM probes by themself is 0.2 ohm. If that matters..
     
    Last edited: Sep 15, 2018

     

    Please register to disable this ad.

  17. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    48,131
    Location:
    Hertfordshire, UK
    Test the driver transistors, take them out - like you did with the output transistors correct? you can't test transistors reliably UNLESS you remove them. It would help if you replaced the bias trimmers completely - they'll very likely be beyond redemption due to age by now.
     
    rotco likes this.
  18. rotco

    rotco Active Member

    Messages:
    157
    Well, i did some progress..
    I took out the output transistors. Suspected channel only - Left.
    Both of them out. I measured and found:
    Tr01 (D188A) shorted
    Tr03 not shorted.

    I did the following while usong DBT 60w 230v:
    powered ON without driver board connected (F-2647) and relay clicked in.
    Powered On while driver board connected (F-2647) and relay didnt click in.
    Edit: DBT was a bit bright. And faceplate lights was dim including dial meters.

    What does it mean?
    How could i procceed?


    I thought that maybe this way, everything would work fine, but i will have a sound only in R channel. Is it correct?
    Would that be the case unless there ia still additional affected components on driver board?
     
  19. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    48,131
    Location:
    Hertfordshire, UK
    It means that there is still too much DC voltage on the output of the amplifier - the protection circuit is detecting this voltage and preventing the speaker relay from clicking, you have to find out why that is.

    Have you taken out and tested all the driver transistors yet?
    Don't worry about ^^this^^ just now, it's a minor detail.
     
    Last edited: Sep 16, 2018
  20. rotco

    rotco Active Member

    Messages:
    157
    Not yet.
    I want to trouble shoot it simply.
    Does everything should be symethric betwwen L/R channel?
    i.e might the relay click in only by one channel is working? (And the other just absent, assume its not shorted)

    Im asking that because this way my next step will be to take out also both driver transistors on the left channel. (The channel on which the output transistors out as well)
     
    Last edited: Sep 15, 2018

Share This Page