Audison SRx2 muting problem - diyAudio
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Old 7th September 2012, 05:25 PM   #1
Mote is offline Mote  Estonia
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Default Audison SRx2 muting problem

I was given Audison SRx2 amplifier to be repaired.

I think something failed in the muting circuit. PS is working properly, amp does not draw excessive current. Input signal is clear and present on all opamps in the preamps section, volume and crossover pots, switches are working properly. No audio on speaker terminals.

I can not find audio signal on any transistors in the audio section of the amplifier, it is very difficult to tell what is what because of all of the SMD components, impossible to see where the traces are going. I found a SMD transistor near thermistor which at first gave me a reading that it is shorted, when this transistor is removed, then amp produces some audio but not anywhere near the power it is supposed to put out. I have not replaced the transistor yet because I have to order suitable replacement.

As I wait for the new transistor to arrive, anyone has the schematic for this amp? Just in case replacing it does not solve the problem.
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Old 10th September 2012, 05:02 AM   #2
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Seems that it is not the problem, I tried a 2SC1815 as a temporary replacement in place of that transistor but that does not allow the amp to produce audio.

Anyone has had similar problems with Audison amps?

I will try to contact Audison as well.
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Old 11th September 2012, 10:32 AM   #3
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What is the DC voltage measured across the base (red probe) and emitter (black probe) of the two transistors in the photo?
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Old 11th September 2012, 04:51 PM   #4
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Transistors are with BBV marking, found from LRx 1.400 service manual, that these are the muting transistors. I get 0,63V across base and emitter (two legs which are on the same side) on both of them.
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Old 11th September 2012, 05:00 PM   #5
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Lift those transistors to see if the amp will produce clean audio. If it does, you'll have to follow the circuit back to see what's driving those transistors.
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Old 11th September 2012, 05:25 PM   #6
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Without those I do not get clean audio, only some crackling when gain is turned way up.
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Old 12th September 2012, 07:16 AM   #7
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Follow the circuit back from the collectors of these transistors. It likely goes through a capacitor, then to a 1k resistor then to an op-amp. Do you have clean audio on the output of that op-amp?
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Old 12th September 2012, 07:50 AM   #8
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I checked that yesterday, I had clean signal on the pads of collectors for those transistors.
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Old 12th September 2012, 09:19 AM   #9
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How close is the schematic diagram that you have?
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Old 13th September 2012, 07:20 AM   #10
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Do you have both positive and negative regulated voltage on the SMD resistors marked 123 located near the emitter resistors?
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