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Old 3rd June 2007, 02:29 AM   #1
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Default lm4780 problem

I've assembled one of BrianGT's LM4780 boards. Turned on the power, no smoke (praise the Lord). No signal from the speakers, just a very infinitesimally small hum. Apparently it's in protection of some sort.

I don't know what voltages and other measurements I should be getting on each pin out. Anyone have any ideas?

No solder bridges, and I've checked my connections several times. It all looks correct. Help?
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Old 3rd June 2007, 06:32 AM   #2
YFW is offline YFW  United States
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Please check the output DC voltage which should be very low if everything is in normal condition.
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Old 3rd June 2007, 01:22 PM   #3
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Default Re: lm4780 problem

Quote:
Originally posted by Jim Karr
I've assembled one of BrianGT's LM4780 boards. Turned on the power, no smoke (praise the Lord). No signal from the speakers, just a very infinitesimally small hum. Apparently it's in protection of some sort.

I don't know what voltages and other measurements I should be getting on each pin out. Anyone have any ideas?

No solder bridges, and I've checked my connections several times. It all looks correct. Help?

How have you connected the MUTE pin?
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Old 8th June 2007, 10:18 PM   #4
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DC voltage is almost nonexistent. It's been so long since I worked on this amp I don't remember the exact value, but I do remember that it was miniscule.

I believe the mute pin is just fed through the board into a plain unclad hole, so it is not connected at all.

Thanks for your responses!
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Old 9th June 2007, 12:38 AM   #5
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Quote:
Originally posted by Jim Karr
DC voltage is almost nonexistent. It's been so long since I worked on this amp I don't remember the exact value, but I do remember that it was miniscule.

I believe the mute pin is just fed through the board into a plain unclad hole, so it is not connected at all.

Thanks for your responses!
Well, ther you go...the mute of the LM4780 needs a few milliamps to turn the amplifier on...see the product PDF.
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Old 11th June 2007, 11:14 AM   #6
sangram is offline sangram  India
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On that particular board (at least the Peter Daniel version) there are two pads that look like surface mount pads on the 'copper' side of the board, where I solderded the mute resistor. It's not marked on the silkscreen, so it's easy to miss.
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Old 13th June 2007, 08:56 AM   #7
zei is offline zei  Sweden
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I did the same mistake
ie, i did not solder the MUTE resistor and i got no sound.

So follow sangram,s suggestion and you will have music in no time

/Z
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