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Sansui Z-7000 Channel imbalance

Discussion in 'Exclusively Sansui' started by Skywatcher, Apr 15, 2018.

  1. Skywatcher

    Skywatcher AK Subscriber Subscriber

    Has anyone ever worked on or serviced one of these? This is not the Z-7000X but is still very similar and may have the same remedy. It is touted as "Super Feedforward" and "distortion killer" at .005% THD. I just picked up a late version of the Z-7000 and have found the left channel is noticeably stronger than the right. There are 2 versions of the "Power Amp" section on the main board. The section with the STK3106. One version has 2 trim pots VR1/VR2 coming off pins 9/10. One is for -25v, and the other +25v. Mine only has VR1 on the board for pin 10 -25v. There is about a volt difference when cold (room temp), then varies slightly as it warms up to about .5v diff. And another thing I noticed when setting the BIAS that the left channel pot has to be to the extreme end of it's travel to bring it down to the 2mv, and it still drifts upwards over 3+mv. The right channel adjusts fine close to the middle of the trimmer. They are a 1k pot and I have Bourns on hand to replace them if need be. I haven't started checking transistors or resistors yet to see if anything is out of tolerance, but I thought I would ask first if there is something to target first and if anyone else has ever come across this behavior in early 80's Sansui gear. I have already replaced all electrolytics while meticulously measuring ESR to keep all values as even as possible between both channels. I am confident they were, and still are not related to this issue. This unit plays and sounds fine otherwise, but the channel difference is quite "bad" so to speak. Yes, I have cleaned the balance pot with CRC QD first, then Deoxit flush, then FaderLube. It is very smooth and responsive so I do not suspect it. I thank you for any insight you can give.

    To Pete; Serial number is 812100202 ;-)


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