Loud humming noise from Sony DAV-DZ151KB home theatre

[newseduser]

Hi
I'm having a problem with my Sony home theatre system. It works fine when an audio CD or some video DVD is played, ie, no humming and crystal clear sound. But on changing the input source to tv(Analog red and white cable), FM, AM or AUX(audio mode), there is a loud hum along with the music. The hum,i think is louder than the music itself. But still,i can hear the song. The annoying hum doesn't go away. It's sound is dependant on the volume set on the system. It's nothing like AC problem or earthing, since then it would have affected the cd playback too. Also,i have another system working fine on the same supply. I know there is something wrong internally, but seriously wish to know what could be wrong, and if possible, try for a self repair.
Edit: Also, with these symptoms, i think the amplifier part is working good. I think something like encoder/decoder is fried, maybe. Could that possibly be it?

 

[helpstar]

Did you try another analog cable?

 

[newseduser]

Yup. Tried all cables. It's not cables fault.
And, the hum is still there even without any cables connected.

 

[helpstar]

Found a service manual
http/www.go-gddq.com/mwg-internal/de5fs23hu73ds/progress?id=hw9JJQVGChLN_5DoJNyceHjHxl3-7QHoroj3W9JcdsI,

maybe it can help to find the defective component

 

[newseduser]

Thanks for the manual, but i seem not able to identify the component with just that. I ruled out the possibility of io-s board being the culprit, by running it with the board disconnected. Now what remains are the main board and another one with the display. The main board has a lot of components, so it is a lot difficult to even identify what could be wrong. But, can weak capacitors cause this hum sound?? I'm really doubting some capacitors gone weak, but there are no bulging ones or that with leaking electrolytes. And as i mentioned it runs fine with dvds or cds playing, the amplifier part of the main board is good. So i think i just need to test the rest of the components. But what could be the best way to test capacitors?? Is it just touching with multimeter in continuity mode and see some values change for an instant, or is there a better way?

 

[helpstar]

Sorry, but I can´t help you in that more detailed. Could be "anything" from here.

 

[newseduser]

Thanks,
I checked out most of the capacitors and i think they are fine. Fed up of all this DIY, I gave it to Sony service centre, and they told some IC had gone bad, and it will take 2/5th of the price of the whole system to repair it. So I just took it to a local service centre and they are now checking it out. But in case the result is negative, can you suggest some other amp for the still good 850W speaker assembly I have with me?

 

[helpstar]

I´m not into this that much, better start a new thread, maybe someone else can help you there.

 

[newseduser]

Thanks for all the help!!