4780 producing only hum: help needed!

zenocosini · 17th November 2005, 07:48 AM

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?

pinkmouse · 17th November 2005, 08:47 AM

Does the volume of the hum change when you turn the volume pot up or down?

zenocosini · 17th November 2005, 09:10 AM

No, not at all.

youyoung21147 · 17th November 2005, 11:41 AM

I got this problem and it came from a desoldered capacitor on the PSU. check them it could just be that

zenocosini · 17th November 2005, 11:42 AM

Seems that I've inverted signal IN and signal ground!

Is the chip ruined ?

pinkmouse · 17th November 2005, 04:07 PM

Unlikely, they are quite robust.

youyoung21147 · 17th November 2005, 04:27 PM

If you get hum on the speakers it means that it is still working !

17th November 2005, 07:48 AM	#1
zenocosini diyAudio Member Join Date: Jul 2005 Location: Padova, Italy	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?

17th November 2005, 08:47 AM	#2
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Does the volume of the hum change when you turn the volume pot up or down? __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

17th November 2005, 04:07 PM	#6
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Unlikely, they are quite robust. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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17th November 2005, 09:10 AM	#3
zenocosini diyAudio Member Join Date: Jul 2005 Location: Padova, Italy	No, not at all.

17th November 2005, 11:41 AM	#4
youyoung21147 diyAudio Member Join Date: Apr 2005 Location: Belfort	I got this problem and it came from a desoldered capacitor on the PSU. check them it could just be that

17th November 2005, 11:42 AM	#5
zenocosini diyAudio Member Join Date: Jul 2005 Location: Padova, Italy	Seems that I've inverted signal IN and signal ground! Is the chip ruined ?

17th November 2005, 04:27 PM	#7
youyoung21147 diyAudio Member Join Date: Apr 2005 Location: Belfort	If you get hum on the speakers it means that it is still working !

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