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T773 hum on mains, not on center. Hum is independant of volume

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I have repaired this problem a couple of times in NAD units and each time it was either a bad capacitor on the board that is vertical right between the power transformer and the heat sink. I can not remember the value of the capacitor, but it was near the middle of the board it is on and had the top of the cap pushed out a little. Or it was cold solder connections on an IC on the digital board. It has been over a year since I did these repairs, so I can not be any more specific due to failing memory. To sum it up for you, you will need to have it serviced by a qualified service technician to have it solved unless you have some very good electronic repair skills. I am sorry I could not be more help, but since this is a very good unit, it would be well worth getting repaired, it is not a cheap-o unit. I have been repairing audio equipment for over 18 years and have gotten pretty good at it, so I am sure the problem you have is not a real major problem, but it really does require some service from somebody who knows what they are doing. You should not let anybody touch it unless they are well qualified, it normally ends up costing even more money for a repair after an unqualified person tries to do repairs that they know nothing about. It is very easy to cause further damage that can be avoided with proper service. sorry i went on so much about this, but I really like the NAD you have and I honestly think you would be better served to take it in for repair.


Posted on Sep 06, 2008


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Loud hum when volume is turned up and ground is attachedntable troubleshooting

Apart from the suggested solutions shown below, you might also want to consider the turntables power supply as the cause of the hum. Perhaps a faulty mains smoothing capacitor?

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It could be the diodes, but whatever is the cause it's before the pre-amp section. Generally a loud hum such as that with no effect by volume control, is mostly caused by the filter capacitor in the power supply. And that hum is the 50HZ mains hum getting into your system!

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Hello sir, hi, missing sound can be costly to repair or needs service by the manufacturer if the problem is the main circuit board. to test, i need you to do something first so as we can find where the problem is. here are the steps. 1. turn on the TV. 2. tune to a program. or watch a movie via DVD. 3. now place you ears near the speakers. 4. do you hear a soft hum? 5. no, set the volume high. do you hear the hum? still no. problem is the amplifier. 6. yes. problem is before the amplifier.
1. problem with the amplifier no soft hum. this problem is due to a failure of the amplifier IC. or an open loudspeaker driver. this you can do, check the wiring of the loudspeaker if it is intact. you may need to disassemble it carefully to have a see. If intact, next is the IC amplifier test/replacement. you need a service technician to do this.
2. problem with the amplifier with a soft hum. this tell you that the amplifier section is good, and the audio source is not reaching the amplifier input. this needs a thorough check on the main board. to conduct this test we need very expensive test instruments, so I suggest have this checked by the service center instead.

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Humming noise when volume over 40

This hum could be from a ground loop or a bad main board in your TV.
1. Try removing all the inputs from the back of the TV.
2. Unplug the TV for about 3 minutes and plug it back in.
3. Turn on the TV and go to HDMI1 input.
4. Turn the volume up to see if you hear the hum.
5. If you hear the hum without any inputs into the TV, then the problem is with your main board, or with the quality of power you have going to your TV (your wall outlet may have an open or bad ground). You can try plugging the TV into a different outlet across the other side of the house (to try a different circuit) to see if your power is the problem.
6. If you don’t hear a hum without any inputs into the TV, then the audio hum is caused from one or more of your inputs.
7. You will have to plug in one input at a time into the TV, and turn up the volume to see if that one input is creating the hum. If the TV hums, then you have a problem with that device and or the cable that connects it to the TV.
8. There is a chance the hum will occur when two or more devices are connected to the TV at the same time. So be careful of this issue. This issue is not the fault of the TV and is a grounding issue between the devices.
I hope this information has helped you.
Good Luck.

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1 Answer

I have Insignia ns-p42q-10a tv, there is a loud hum when the volume is on when you mute the volume it goes away? Any suggestions?

check other inputs AVI, HDMI,,

do you here the hum on all inputs?

The hum maybe from a bad ground loop,, unplug all pluged in inputs, [dvd,games,radio,ect] <--check for hum.

If the hum is gone, plug inputs back in one at a time and test,,

When you find the source of the hum, go get a ground loop isolator to fix.

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My sansui qs 1 immediatly stopped working and alll it does is hum can not find any burnt components

Good day sir, there are several reason why the amplifier hums, but lets go to the common ones,
  1. The main power amplifier is defective. Does the volume control affect the loudness of the hum? If no, possibly replace your main amplifier IC. if its transistorized, check the two push pull amp. for shorts.
  2. If Yes, check for shorted audio cables. just maker sure you are using a good audio cable. or
  3. The pre-amp IC is defective, usually op-amps. try replacing them one at a time. these requires unsoldering and soldering.
  4. If you want to find the faulty part, you may need to trace a signal, you may need the folowing, an audio source, sine wave generator, an oscilloscope, or a portable amplifier. This method requires you to be techie. Feed the input with the audio source (disconnect first the speakers so that the hum will not bother you.) check the output of each stage, from preamp to power amp. identifying where the heck the signal dissapper. and where the start humming appears.
The third one requires a lot of work, just bring it to a service center.
Hope this helps, feel free to ask again, let me know your progress. Thanks

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I fixed the same issue by replacing the original AC power supply with a 13.8 volt DC power supply (Radio Shack) It seems to be more consistent at high SPL and no hum , as the Boston acoustic unit accepts either AC or DC power.

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Onkyo HT-SR800 buzzing noise present then vanishes

The hum a fluorescent light makes is the 50 or 60 Hz hum of the alternating current mains supply. Inside the light fitting is a choke which when less than perfect tends to hum. When the choke is loose internally or externally is when the hum becomes an annoying buzz.

When an audio system has a similar tone of buzzing or humming the source will invariably be the same AC mains but how it got in there is difficult to answer...

It could possibly be poor smoothing and regulation of the power supply or an accidental hum loop caused by careless design and/or poor grounding. It could be caused by being induced in the input by connecting leads that are too long and poorly positioned/screened or it could be caused by mismatch between different components causing a poor signal-to-noise-ratio.

I am not sure why it should come and go but the fact it does would indicate a power supply problem more than the other possible causes.

If the Onkyo system has it's own volume control and it is being used witha tv or similar, it is worth trying to imporove things by turning up the tv volume to near maximum and then controlling the volume with the system control.

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