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Pioneer SA-1000 power output trans problem.

V

vhinx

New Member
Hello Guys, I'm newbie here...

My pioneer SA-1000 int amp has problem before due to encountered blown main fuse, the root caused was busted/shorted 2pcs. Toshiba 2SC1080 power output transistor on the Left channel power amp... But when I replaced it with substitute ON Semi MJ15015, it shown on DVM that the reading on "idle current adjustment" was too high (Left channel: 125-130mv Right Channel: 02.3-02.5mv) even adjusted the VR4 at the minimum...
 
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try a 2.2k resistor in place of r40's (r39?) 2.7k (the one connected to the emitter of the transistor who's base is connected to the pot's wiper).

I haven't calculated it, but that should get you into the voltage range.

On semi's seem to have a bit lower turn on voltage emitter to base, which results in higher idle currents for a particular voltage.

OR, set the pot to minimum, connect a 50k or so external experimental pot across that 2.7k resistor and decrease the pot's resistance until you get low (but NOT OFF) idle current. Then read ohms across the two (2.7 k and paralleled pot) to get a resistance value to sub for the 2.7k.

This of course assumes that everything else is working ok. To absolutely test this, swap both output transistors channel to channel, and see if the symptoms follow the output transistors.
 
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Hello Guys, Sorry for the late reply due to my work...

Here we goes, already check all resistor & Transistor for continuity and resistance test but in all good and very minimal difference compared to other (right) main amp.

Changed resistor value 2.7K down to 2.2k at r40 but seen the idle current was being higher than before...

Sir Mark, Do you mean that I need replace 1.5K trimpot with value of 50K for experimentation if the idle current is going down???

Already tried to interchanged both power (Left-2pcs.MJ15015 & Right-2pcs.2SC1080orig) transistor but problem still remained... now, The Left channel main amp used 2pcs.2SC1080 with idle current start from 60mv to 140.0mv at pot minimal position and Right channel main amp used 2ps.MJ15015 with stable idle current of 2.5mv.

Very appreciate your prompt reply guys... Thanks!
 
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