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Old 9th July 2010, 01:23 PM   #1
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Default Quad 405-2 Problem

Hi, I wonder if anyone can help me with this. One of my boards M12565 iss 6
has blown R38. When switched on the resistor glows bright red at which point I switch off! I've read the Quad service data and have checked D5 and D6 which it states may cause the problem. I unsoldered them and they are fine.

I'd be grateful for any assistance with this.

Thanks for looking
Peter
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Old 9th July 2010, 03:21 PM   #2
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Hi!

Check output DC offset voltage (meausure voltage on +/- speaker terminal)
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Old 9th July 2010, 03:35 PM   #3
cda is offline cda
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Also check R7 and R8, they are rated very conservatively, and should be replaced with metal oxide resistors of (at least) 1W.
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Old 9th July 2010, 03:47 PM   #4
405man is offline 405man  Scotland
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I would disconnect the DC offset protection by unsoldering the blob next to the output terminal then check the output offset voltage, this should be a few mV. The CD protection triac goes s/c. Then I would check both supply voltages and the supplies to the opamp.

Stuart
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