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Onkyo amp woes!
Onkyo amp woes!
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Old 11th June 2013, 10:34 AM   #1
Charlie111 is offline Charlie111
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Join Date: Dec 2011
Default Onkyo amp woes!

Hi folks I am really struggling with an Onkyo amp for which I cannot find a scematic, it is an itegra A-819. Some of the driver trannys are dead in the left channel can I replace 2sc2238's a968's & 2sc1940's & A915's with all 2sd1138's & 2sb861's, I should imagine gain is surely not a problem! The other channel I am having trouble with the bias, I am measuring zero across the emitter resistors (0V on output with healthy main power supply, and healthy 22v secondary supply to opamp) and when injecting a sine wave this is appearing as a saw tooth on the output :-( I have not come across this particular diff amp and current source configuration before, not to mention the active bias and cannot find any obviously faulty components! Any help would be appreciated! Thanks.
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Old 11th June 2013, 04:41 PM   #2
east electronics is offline east electronics  Greece
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Measure if there is proper supply in the drivers ..often drivers are powered after fusible resistors in the area of 10 ohm or so if one of them is blown you get no drive no bias ...

also look at the obvious poor soldering , broken traces , and open resistors ...

In between i will take a look for a schematic also
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Old 12th June 2013, 02:15 PM   #3
Charlie111 is offline Charlie111
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Hi Sakis thanks for the reply, supply to the drivers is fine as far as I can see, and there are no fusible / out of range resistors :-( The OPamp, part of the servo bias seems to be outputing 2.5V with zero on the output which I would not expect though!?
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Old 16th June 2013, 08:09 PM   #4
Charlie111 is offline Charlie111
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Join Date: Dec 2011
hi folks I have stuck this to one side at the moment, but if anyone could give me any pointers, or help with a diagram I would be quite grateful :-)
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