Surround sound system repair

[Joe Martinez]

I have a 5.1CH Surround AV Amplifier Package (Model UBR510B) that I was given from a friend. He told me he plugged it into a 240V outlet while the device was set to 120V. He replaced the fuse in the power inlet to the device, but now whenever the device is hooked up and turned on it makes a humming sound. I opened the main hub and all the Electrolytic capaciters look fine, there arent any additional fuses that I've notices internally, I did notice a ceramic capacitor was missing but I dont know what size it's supposed to be without the schematics. All the solder joints look fine and nothing seems to be damaged. Does anyone know how to test relays to see if they're busted? or does anyone have any advice on the source of the issue?

 

[Technician Tonny]

In most amplifier circuits relays are used in delay circuits, switching the amplifiers B+ wire to the supply voltage or connecting speaker's wire's to the speaker left and right connections...

To test a relay u just measure across its coil using a multimeter, rotary switch at diode position.. and you will get a reading btn700 ohms and 1k,
There's a diode across it, so to test it accurately i suggest to first solder the relay out, and u can test t using external supply in this method u first know the relays voltage by looking on it, u will see its voltage printed on it, after u apply the required voltage to its coil, u will hear a click sound inside the relay

But if u able to hear some humming sound the relay may be working fine.. that sound maybe a fault of amplifier Ic, feeding DC signal to speakers

Remove the speakers and connect a multimeter to the sp - and sp + of the amplifier,
set the rotary switch to 20 DCV , if u get any voltage reading from 1vdc to 20vdc and above the Ic is fault, u should get a reading btn 0.30 /0.80vdc
a good amplifier should output Ac signal,

 

[duke37]

The relays in an amplifier are most likely to be run on DC and will not hum. If the amplifier works, then the relays are working.

Is the hum coming from the amplifier or a speaker?
If the hum is coming from the amplifier then try to find the component which is vibrating.
If the hum is comming from a speaker, then a big electrolytic capacitor is likely to be the culprit.
They can be disconnected and tested for capacitance and ESR. Alternatively an oscilloscope will show where there is a large voltage ripple.
A spare capacitor can be probed across each capacitor to hear if the hum is reduced. Get the polarity correct.

 

[tedstruk]

listen where the buzz is coming from. Replace whatever is buzzing.
What you need to know is that if the fuse blew, it did its job, and that usually means everything is ok. Maybe, the unit buzzed when it was new.