Question about Audio & Video Receivers
When you say it turn on-off you're not able to establish your audio out right? the possibility is that you have a bad speaker causing the system (aa8080) to trip. have you tried turning on without the speakers. can you try it first and then find out if it still does the same. because if there is something wrong in your output stage, you should not get that ticking/switching sound, it is not suppose to turn on (output stage) because that switching you can hear is actually your proitection circuit.
Posted on May 03, 2008
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I have had problems with this stereo mixer amplifier which had the symptoms of no sound output from either channel .
I opened up the unit and discovered that the amplifier was correctly amplifying my input signal up to a relay which switches the output through to the speakers .
This relay did not activate at all.
When the power switch is turned ON you should hear a click approximately 2 seconds later , if no click then there is a problem with the circuitry associated with this relay .
I traced out all the connections associated with this relay and made a circuit diagram .
The relay is a 24v relay and I will explain the way that I can see that this section of the amplifier works.
It has been designed to ;
This it needed because otherwise there is a current surge and sparks from the relay turning on immediately.
Q804 turns On Q805 which turns On Q806 to activate the relay .
Voltages on transistors
Q802 and Q803 2sc1815
Base 0V Collector 12.9V Emitter 0V
Base 12.9V Collector 0V Emitter 15.1V
Q805 2sc1815 (driver for Q806)
Base 0V Collector 7.2V Emitter 0V
Base 0V at Turn ON then after 2 secs increases to 0.7V
Collector 2.8V ( transistor is activated as a switch Turned Fully ON ( saturated) to turn on the Load which is the relay .
I have replaced the following transistors to fix my amplifier q805 2sc1815 and q806 2sc1815 .If you are going to use a different type of transistor it may not work and also the lead connections of a 2sc1815 for the collector and emitter are different to those such as on a 2n2222( transposed).
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