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Amp Gurus - HELP! NAD 3020A
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<blockquote data-quote="gbyleveldt" data-source="post: 62019" data-attributes="member: 122"><p>Maybe I'm blind but I can't find R646. Anyway, for Q609 to fail in the way it has both Q611 and Q613 must've failed. In order for those to fail, either or both output transistors had failed. The output transistors and Q609 are really cheap, not sure about the others though. It's easy enough to check with your meter set to diode though. Remove all the transistors mentioned here and use your meter to check for shorts across the pins. That'll be a dead giveaway. After that, check that you get the .6V drop across the BE and BC junctions, if not the transistors have gone open. Due to the nature of the failure, I doubt they failed open though.</p><p></p><p>Edit: Check R651 and the diode in series with Q609 as well...</p></blockquote><p></p>
[QUOTE="gbyleveldt, post: 62019, member: 122"] Maybe I'm blind but I can't find R646. Anyway, for Q609 to fail in the way it has both Q611 and Q613 must've failed. In order for those to fail, either or both output transistors had failed. The output transistors and Q609 are really cheap, not sure about the others though. It's easy enough to check with your meter set to diode though. Remove all the transistors mentioned here and use your meter to check for shorts across the pins. That'll be a dead giveaway. After that, check that you get the .6V drop across the BE and BC junctions, if not the transistors have gone open. Due to the nature of the failure, I doubt they failed open though. Edit: Check R651 and the diode in series with Q609 as well... [/QUOTE]
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Amp Gurus - HELP! NAD 3020A
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