Hi Friends,i hope you all doing good

Friends i am having a problem with thid 5.1 home theater. It started with continuous relay sound few days back then today morning it is not giving sound output (in full volume it gives low volume sound)

So while checking the components when i put the ground of multimeter to ground of board and the positive of the multimeter to one of the transistor near relay pin (pics attached) it starts to work fine. But when i turn it on again, it doesnt work

I am new to on board fault findin so i unable to find the fault. If anyone have experience like, please help

Thanks in advance!


EDIT 1 :
after looking at board carefully , i found out that relay is used for connecting the speakers to amplifier.

 

Hard to tell without a schematic. The transistor in question (photo #2) has a 10K resistor connected to what appears is the base. This connection continues down to the left of said resistor to a connector at the corner of the board. I would check the traces on the pcb first to verify continuity.

 

If touching it with a meter probe makes it work, it might be an intermittent connection that can be re-soldered. So next try touching in the same place with a toothpick or other non-conductive item to see if just a touch makes it work. If you are able to solder well, with all the power to the thing off and disconnected, and that may solve the problem. But if you are not quite good at soldering do not try this.

 

Hard to tell without a schematic. The transistor in question (photo #2) has a 10K resistor connected to what appears is the base. This connection continues down to the left of said resistor to a connector at the corner of the board. I would check the traces on the pcb first to verify continuity.

If touching it with a meter probe makes it work, it might be an intermittent connection that can be re-soldered. So next try touching in the same place with a toothpick or other non-conductive item to see if just a touch makes it work. If you are able to solder well, with all the power to the thing off and disconnected, and that may solve the problem. But if you are not quite good at soldering do not try this.

I
Hi thanks for reply. I check the continuity and it the component are soldered well. I think its could be relay problem (maybe) cause when i touch with non conductive it does nothing. When i try turning it on-off multiple times it does turn off.

Could it some prob with relay. Attach is relay pic

 

Could it some prob with relay.

When the unit is working correctly does the relay engage to connect the speakers after a short delay?
Or does the relay only engage to disconnect the speakers if there is some kind of short or overload condition?

 

When the unit is working correctly does the relay engage to connect the speakers after a short delay?
Or does the relay only engage to disconnect the speakers if there is some kind of short or overload condition?

Its connect to the speaker quickly but only once its properly activated (the clicking noise that comes from it can tell if its properly activated ). When its not working , either the relay make no noise or it does does partially.

And the relay dont disconnect the speaker as long as its been manually turned off.when its working its working fine.

 

It is also possible that the relay is protecting the speakers from some problem with the amplifier, which is what it is supposed to do. If the amplifier has an excessive DC offset then the relay is not supposed to connect the speakers. So the problem might be with the amplifier circuit, not the relay circuit.
That is, the relay might be working exactly like it should. The problem may be elsewhere in the amplifier. THAT will require some testing to verify.

 

What MisterBill2 said above is very true it might be a whole different problem but there are a few measurements who can take with a DC voltmeter that should be able to verify if the relay circuit is at fault. Further examination of the top and bottom of the pc board shows a darlington configuration of the two transistors that drive the relay. I believe that circuit is similar to the one I'm posting below.

 

It is also possible that the relay is protecting the speakers from some problem with the amplifier, which is what it is supposed to do. If the amplifier has an excessive DC offset then the relay is not supposed to connect the speakers. So the problem might be with the amplifier circuit, not the relay circuit.
That is, the relay might be working exactly like it should. The problem may be elsewhere in the amplifier. THAT will require some testing to verify.

but amplifier works fine when once its working . i have feeling there is some problem with IC that send signal to relay. could it be reason

What MisterBill2 said above is very true it might be a whole different problem but there are a few measurements who can take with a DC voltmeter that should be able to verify if the relay circuit is at fault. Further examination of the top and bottom of the pc board shows a darlington configuration of the two transistors that drive the relay. I believe that circuit is similar to the one I'm posting below.
View attachment 220312

i will check it again with above details. they are indeed connected to some kind of transistors.

 

Update : i have tried to bypass the relay switch and now its working just fine.please find the attached image.
kindly let me know if it gonna cause any harm to system or ic.

 

It can allow you to use the amplifier until some fault in the system causes some voltage that would damage the speakers. In addition, you will hear all of the turn-on thumps and pops.
So still, you need to take the advice and measure the DC voltage across the speaker terminals with no sound playing. So you can trurn down the volume control to make the measurement. There should not be any DC voltage across the speakers if the amplifier is working correctly.

 

but amplifier works fine when once its working

But it may sound fine, even if there is some DC on the speakers.
Do as MB2 suggested and measure the speaker DC voltage with the relay closed but the volume turned down.

 

It can allow you to use the amplifier until some fault in the system causes some voltage that would damage the speakers. In addition, you will hear all of the turn-on thumps and pops.
So still, you need to take the advice and measure the DC voltage across the speaker terminals with no sound playing. So you can trurn down the volume control to make the measurement. There should not be any DC voltage across the speakers if the amplifier is working correctly.

But it may sound fine, even if there is some DC on the speakers.
Do as MB2 suggested and measure the speaker DC voltage with the relay closed but the volume turned down.

Thanks again for replying !

I have done as u said , i ve desoldered the wires i put before to jump the relay and tested the dc voltage on speaker connectors with volume off and theres no voltage on any of five speakers output.
Do i need to check anything else too ?

@misterbill you're right with those speaker making thump noise when i turn it on.is it not good ?



p.s. : even while music is playing on loud its not showing any dc current on outputs.but if i do the multimeter switch from 20 to 200m

 

If the relay was not activated and the bypass removed then you measured NOTHING. The purpose of the relay is: First, to keep the amplifier turn-on transients from damaging the speakers, and Second, to protect the speakers from DC voltage if some part of the direct coupled amplifier fails.
Our intention for the test was to reveal what the output voltage would be with the amplifier connected to the speakers. Removing the wires that bypassed the relay contacts prevented that from happening.
OR, you can measure the voltage just before the relay contacts. although that will be a bigger challenge to do safely.

 

If the relay was not activated and the bypass removed then you measured NOTHING. The purpose of the relay is: First, to keep the amplifier turn-on transients from damaging the speakers, and Second, to protect the speakers from DC voltage if some part of the direct coupled amplifier fails.
Our intention for the test was to reveal what the output voltage would be with the amplifier connected to the speakers. Removing the wires that bypassed the relay contacts prevented that from happening.
OR, you can measure the voltage just before the relay contacts. although that will be a bigger challenge to do safely.

I understood your point and have remeasured it by Bypassing the relay and it still shows no voltage there as such. after removing the multimeter probes i connect the speaker wires back and turn on the volume it plays fine

 

I understood your point and have remeasured it by Bypassing the relay and it still shows no voltage there as such. after removing the multimeter probes i connect the speaker wires back and turn on the volume it plays fine

Then it appears that there is a failure in that relay circuit at some point.