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Sony str 6800 issue

S

StickWeapon

New Member
Hllo everyone. I have problem with this little buddy :( i have done full recap also dual cap, changed faulty (hot) resistors 560 ohm for 5 watts, changed relay and sometimes have problem with right channel, on 0 level i hear little scratchy and sometimes loud crackless, sometimes relay can click, before recap also... i think may be some transistor bad. After 10 minutes all will be ok but the problem remains. Maybe You has that problem too. I have experience with vintage audio but maybe you will speed up the process. Maybe You have good substitutes for all Q on main and phono board. Thank You!
 
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I went with the STR-6800SD service manual. I hope it is identical to your unit. In the power amplifier stage there is a dual PNP transistor at the input. This is Q701 (L-ch) and Q751 (R-ch). When they were new, both transistors inside those dual transistors were matched. With time they may drift and become mismatched. You must pull out those transistors and mesure the hFE of each side. If they differ by 15% or more (inside a single dual transistor), they will generate loud scratchy noise. This is the reason why the popular 2SA798 figures on the list of transistors to replace. The 2SA884 is not on that list but can be as problematic. Replace them by a pair of hFE matched KSA992.
 
To be sure that the problem is in the power amplifier section, can you disconnect the red wire (R-ch input) on pin 1 of the connector located between Q701 and Q751?
 
Already checked preamplifier after disconnect and then ill put wire from ground to ground of preamp. I found guilty :) that's q754 (2sc1904). After replace now is problem with left channel. Any good substitute for them?
 
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I decided to put original 2sc1904, working excellent! Possible begginings of problem with 1904, one channel was little foggy, transformator little noisy, sometimes different volume (once louder, once quiet) on the same volume, no "magic" in sound sometimes blurry and loud. Now that buddy sound great like never before! It's working with pair of carbocon ss 5050 and ps 6750 turntable. Thanks for help! Topic can be closed.
 
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