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jeeva 18th September 2010 01:07 PM

yamaha amplifier AX-700
Hi I have just joined the forum and new to this . I am trying to repair my Yamaha AX 700 . I have the left channel working . I have ran comparisons against the right ch. which keeps blowing the outputs , driver and predriver transistors. I have noticed that the dc . voltages on the emitters and base of the working channel as well as the blown channel pulses.The collectors are stable at -64 and +64 . any one has any suggestions
South Africa

Shaun 18th September 2010 04:53 PM

Hi Jeeva

Where did you buy your replacement transistors? Are you aware of the proliferation of counterfeit transistors? See here Counterfeit Transistors .

What are the device types?

Mooly 18th September 2010 05:08 PM

We would have to see a circuit.
Also always use a bulb tester in the mains lead... it will avoid destroying transistors.

jeeva 19th September 2010 04:20 PM

yamaha Ax 700
Hi shaun ,thanks for the reply and my thanks to Ebbe for the schemastics.
I have purchased the output transistors from a supplier here in Durban ,South Africa. Yes I have heard from Jim in Madrid about the suspicious components been supplied worldwide. I have been directed to a company in Johannesburg to repurchase my components needed, Your suggestion about the spares used been faulty is believable ,since all measurements against the working channel seem okay. I will be getting the new spares on Monday . I will keep you posted
Best regards,

Shaun 19th September 2010 05:16 PM

The problems you describe mirror my experiences with fake transistors. I do not trust the local outlets such as Communica, etc. Perhaps the official distributors are a better bet, but they usually demand minimum order quantities such as a full stick of 25 devices. For Sanken devices I finally resorted to importing.

jeeva 19th September 2010 09:40 PM

AX-700 Yahama amp.
The outputs are 2SC3182 x 2 and 2SA1265 x2 other transistors are 2SC3298,2SA1846 ,2SA1015,2SC2240,2SA970. Shaun please let me know where you are getting the originals .
Best Regards,

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