pioneer A-80 no sound

A-80

testing Right channel first, Emitter readings only, Red lead to Emitter black to ground. Large transistor NPN 13mv
Large PNP 8.0mv
small PNP 79V
small NPN -79v
Left channel Large NPN 56.6v
Large PNP -56.9v
Small PNP 78.6v
Small NPN -79.6v
 
That is a very unusual output circuit. The output transistors are the 2sa1295 and 2sc3264 pairs Q1-Q4. Their emitters should be 0. I am assuming the left channel has a problem. I also assume the 56 volts you are measuring is the same polarity with respect to ground. please recheck the readings.
 
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A-80

All emitters are testing with Red probe to emitter and black lead to ground. Right channel Large emitter NPN 8.5ma
large PNP 7.0 ma
sm PNP 80v
sm NPN -80.7v
Left channel LG NPN 57.2v
lg PNP -57.5v
sm PNP 80.5v
sm NPN -80.7v
 
We are measuring volts now not ma ( I am assuming you mean mv). Check to see if the left channel emitter resistor is open it ties the large npn and pnp emitters together. I suspect it is. Start checking the drivers pre drivers as well.
 
Also check the output transistors for shorts. All these tests are done with ohm meter. amp should be off and unplugged.
 
A-80

I will unsolder them and check each transistor. The ER is on the top of the board so it may take some time. As far as drivers and pre drivers which board and transistors are you referring? Is there a source for the output transistors?thanks for the help
 
It is not really necessary to unsolder them. Just measure base to emitter and base to collector. Sometimes they short emitter to collector as well. If there is a short you will see it. The unit has a lot of transistors and diodes. All semis on the channel must be checked. It is a complicated unit. tough one for a beginner. DC amps tend to blow a lot of parts.
 
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A-80

Their are 2 left channel output transistors that are bad 1- 2sc3264 and 1- 2sa1295 , also output assembly has 1- 2sc2275 bad. The other outputs assembly transistors are good. Is there a source for these? Also how do I test R105 in pic. It has 3 legs and what reading is acceptable, it is a .22/5Wx2. thanks
 

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A-80

Thanks for the source. In regards to the parts that check good, which should I order? Thanks
 
Order several of each semi in the unit. I am sure there will be more wrong than just what you found. build a dim bulb tester as well. there are threads discussing it.
 
Their are 2 left channel output transistors that are bad 1- 2sc3264 and 1- 2sa1295 , also output assembly has 1- 2sc2275 bad. The other outputs assembly transistors are good. Is there a source for these? Also how do I test R105 in pic. It has 3 legs and what reading is acceptable, it is a .22/5Wx2. thanks

The center lead is common, so it's 0.22 ohms from either end to the center lead and 0.44 ohms from end to end.

If one output transistor in the channel is bad, it is a VERY good idea to replace them all as a set, especially if this was from a fault and other damage occurred.
 
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