4780 producing only hum: help needed! - diyAudio
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Old 17th November 2005, 07:48 AM   #1
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Default 4780 producing only hum: help needed!

One amp of a dual mono kit from audiosector.com produces only a hum
and few music only when volume is tourned at max.

The voltage between the speaker pole is +12 mV

I suspect I bourned the chip because before I put it into a case everything was ok ( but I couldn't say how it happened).

Is there something to verify to understand what's wrong?
Any idea what happened?
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Old 17th November 2005, 08:47 AM   #2
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Does the volume of the hum change when you turn the volume pot up or down?
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Old 17th November 2005, 09:10 AM   #3
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No, not at all.
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Old 17th November 2005, 11:41 AM   #4
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I got this problem and it came from a desoldered capacitor on the PSU. check them it could just be that
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Old 17th November 2005, 11:42 AM   #5
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Seems that I've inverted signal IN and signal ground!

Is the chip ruined ?
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Old 17th November 2005, 04:07 PM   #6
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Unlikely, they are quite robust.
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Old 17th November 2005, 04:27 PM   #7
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If you get hum on the speakers it means that it is still working !
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