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Sansui amp au11000

The driver board keeps burning out transistors when a signal is applied, it had 4 stuffed output transistors when i got it ,i replaced all 8 of these these but it burnt out left side of driver board when signal was applied, i replaced those then i applied power it was ok as before until i applied signal,this time it was right side, 8 transistors burnt out .ihave since found a dicky varistor? double diode? on the regulated power supply & protector board! would that be the cause of my woes? what do you think! i have had some suggestions from ginko,but i think he needs more info (here it is) regards ross

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  • redrooster Sep 05, 2008

    hello dan,i replaced transistors after left channel burnt out,5,6,7,8,11,12,13,14,15,16,17,18,19,20,21,22, on board f-2580 & resistor r19,r25 &,diode 01, on f-2568,then right side did the same, replaced,6,8,12,14,16,18,20,22,on f-2580.because i cant get originals they are all subs,including outputs mj 15024,mj 15025,they are 250w! i was told they would be ok? before it smoked up last time, the protector light would come on then go off

  • redrooster Sep 05, 2008

    ok dan i have no idea what you are talking about,do i take the output transistors out of the heatsinks,then measure from the pads on the heatsink where the transistors were? if so,do i leave the driver board out? i take it that (to ground) means the chassis, what about +/- 0.6,b+/b-,0.0,is that from base ,collector, emitter,if so what is meant by by b+/b- isnt that the power supply rails?confused ross.

  • redrooster Sep 07, 2008

    hi dan,before i do what you have suggested,i think i still have a problem with the driver board ,im measureing 3m ohms on left channel & nil on right channel,between collectors on tr19,tr21 , & tr20,tr22 ,im sending photo,hope you get it.regards ross. ps no i can not send photo this web page is ********,ive been trying for two days now! what we have here is a failure to communicate, can you send me an ordinary email address please,its getting that frustrating im nearly tearing my hair out,im trying to fix a problem here,but all ive got is another problem shoved in my face

  • redrooster Sep 08, 2008


    1. -57.1v,-0.750,-0.770 /+57.1v,-0.743,-0.723/-57.1v,-0.718,-1.452v +57.3v,-0.716,16.8mv, here are the mesurements,there counterparts are identical


  • redrooster Sep 09, 2008

    well is that it? ive reported a problem with your web site, so now you wont help me,i am disappointed with your unprofessional approach to the problems at hand dan. do i get a refund?or are you going to help me with this? redrooster.

  • redrooster Sep 12, 2008

    hi dan, i have done all that you suggested & have replaced all transistors with relevant subs that hasnt fixed it, so im replacing the electrolitics next, that must be the problem! ( i hope )will let you know how i went when i install them.ross

  • redrooster Sep 28, 2008

    the 100uf caps on the driver board have gone high,out of the 4, one of them is ok the other three are from 124uf to 138uf, i have ordered some more, still waiting for them.everything else measures ok

  • redrooster Oct 02, 2008

    the only thing i can find wrong is the driver caps 100uf,80v 85 degree elna, 1 out of 4 is correct the others are 124uf 126uf 138uf, i cant seem to find any of the right voltage,would 100v be ok or will there be problems with that, as i said everything else checks out ok from power supply on .redrooster

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Check for open resitors (All Values)..also make sure that any diode stacks (Varistors) are not open or shorted....mostly make sure you have replaced the BIAS POT! Lastly U could check for open traces and bad solder joints..also look for tiny solder bridges under an eyeloop magnifier on foil side of PCB>especially after replacing multiple components.

Eric

Posted on Jan 16, 2009

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Without seeing the amp nor having the service manual in front of me, it sounds like you have a severe offset problem. There is either an open resistor or transistor in the early stages. With the output transistors removed from the unit, look around at voltage levels to determine where the fault is. I will try to locate the service manual. Can you post the parts that you have replaced?

Thanks,
Dan

Posted on Sep 04, 2008

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  • ABRsvcs Sep 05, 2008

    I don't have a schematic so the references you posted don't help much. But in general, remove the output transistors completely and measure to ground using a DC voltmeter, each of the 3 pads per output transistor. These pads should measure as follows:



    +/- 0.6V, B+/B-, 0.0



    If they do not, please post the readings here and I'll attempt to help with the next step.



    Dan

  • ABRsvcs Sep 05, 2008

    Ok. Remove the transistors completelyand measure the pads that remain. Connect the black to ground and use the red to get hte measurements from each pad. Each pair should measure as follows (total of 6 pads):



    0.0

    0.6

    B+ (supply voltage probably between 40-70V)

    0.0

    -0.6

    B- (supply voltage as above but negative)



    The driver board must be installed. All that you should have done at this point is to remove the output transistors. The above should be the same for left and right (6 measurements per side).

    Dan

  • ABRsvcs Sep 08, 2008



    i'd like to help further but am restricted by the agreement I have with Fixya form posting any email for direct contact. All I can do at this point is to direct you to a servicer. Where are you located?



    Dan

  • ABRsvcs Sep 10, 2008

    I'm sorry for the delay, but I just received notification that a response was made to this problem.



    Now for the problem at hand:



    One channel is definately incorrect. Where you have the -1.4V should be -.7. I would guess that one of the transistors on the driver board is shorted or its compliment is open. As long as the output transistors are out of the circuit, you should be able to run the unit and track down the offending part. The only thing I can suggest is to A/B the unit. In other words measure the left and right sides. They should be identical. Also, within each channel, the + and - sides should be similar. You will need to change the transistors at the driver stage to make the voltage readings match. Look for low valued resistors that may be open and/or the transistor pairs at the driver stage. Always change the transistors in complimentary pairs.



    Keep me posted.

    Dan

  • ABRsvcs Sep 12, 2008

    Ross, while possible, it is unlikely that caps are the problem. Look instead for open low values resistors. Also, check the power supply areas. Specifically, the low voltage supply. If you have an offset, perhaps one side of the supply is bad. In that case, a bad cap would likely be the problem.



    Keep me posted.

    Dan

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