Hello everyone,
I've tried searching the forum and the whole internet but I wasn't able to find anyone with exactly the same problem. I am an amateur electronics enthusiast with only a basic understanding but I love learning more and more as I go along and I'm not afraid to try.
Anyways, recently I picked up a "for parts" music hall 15.2 amp for 60$. I'd figured I'd take the gamble and even if ultimately it doesn't work I would have had a fun project. The amplifier turns on as usual but after couple seconds (I am assuming this is the speaker relay clicking) it starts to buzz very loudly. Speakers buzz when connected as well, even when the volume is all the way down, though I didn't try much since I didn't want to fry them. The buzz is coming from the right channel on the chassis but I can't pinpoint the cause. I've taken readings from the transistors that are attached to the heatsink and the buzzing channel seems to have a slightly lower voltage. I've also touched up the connections on these transistors and the capacitors just to make sure that it is not from bad solder. The problem wasn't resolved.
Can anyone point me to a solution? Is it bad capacitors? Is it the white ceramic thing that I am not sure what it does?(I am not sure but the buzz might be coming from that component) I've attached some pictures and a video of the buzz. Hope it helps. I know that I sound like such a newbie but I am looking forward to hear from you all. Thanks a lot!
Photos:
Video link:
YouTube
I've tried searching the forum and the whole internet but I wasn't able to find anyone with exactly the same problem. I am an amateur electronics enthusiast with only a basic understanding but I love learning more and more as I go along and I'm not afraid to try.
Anyways, recently I picked up a "for parts" music hall 15.2 amp for 60$. I'd figured I'd take the gamble and even if ultimately it doesn't work I would have had a fun project. The amplifier turns on as usual but after couple seconds (I am assuming this is the speaker relay clicking) it starts to buzz very loudly. Speakers buzz when connected as well, even when the volume is all the way down, though I didn't try much since I didn't want to fry them. The buzz is coming from the right channel on the chassis but I can't pinpoint the cause. I've taken readings from the transistors that are attached to the heatsink and the buzzing channel seems to have a slightly lower voltage. I've also touched up the connections on these transistors and the capacitors just to make sure that it is not from bad solder. The problem wasn't resolved.
Can anyone point me to a solution? Is it bad capacitors? Is it the white ceramic thing that I am not sure what it does?(I am not sure but the buzz might be coming from that component) I've attached some pictures and a video of the buzz. Hope it helps. I know that I sound like such a newbie but I am looking forward to hear from you all. Thanks a lot!
Photos:
An externally hosted image should be here but it was not working when we last tested it.
Video link:
YouTube
How buzzarre. I guess when it comes to doorbells you are already covered? 😉
That sounds like some major sparking. My first thought would have been insulation failure between one of the power Darlingtons and the heatsink (doesn't look like silpads, so probably mica washers + heatsink compound, maybe one of those was accidentally omitted?), but why then would it only commence after a few seconds? Perhaps whatever it is that makes it do this is coming out of the previous stage and needs to be unmuted first?
Idea #2 would be a loose winding on the mains transformer. Loose anything on a transformer can make quite the racket, and it's right next to the suspect channel.
The "ceramic thing" is a dual resistor. If you look at the lettering it says 5 W and something x2, probably 0.22 ohms. These do not generally tend to be highly microphonic.
In a case like this it would be handy to have some of the following tools at hand:
* a multimeter (verify DC offset between center connector of said dual resistor and ground)
* a little microphone
* a scope
* a signal tracer
That sounds like some major sparking. My first thought would have been insulation failure between one of the power Darlingtons and the heatsink (doesn't look like silpads, so probably mica washers + heatsink compound, maybe one of those was accidentally omitted?), but why then would it only commence after a few seconds? Perhaps whatever it is that makes it do this is coming out of the previous stage and needs to be unmuted first?
Idea #2 would be a loose winding on the mains transformer. Loose anything on a transformer can make quite the racket, and it's right next to the suspect channel.
The "ceramic thing" is a dual resistor. If you look at the lettering it says 5 W and something x2, probably 0.22 ohms. These do not generally tend to be highly microphonic.
In a case like this it would be handy to have some of the following tools at hand:
* a multimeter (verify DC offset between center connector of said dual resistor and ground)
* a little microphone
* a scope
* a signal tracer
Haha, yes it is definetely louder than my current doorbell thats for sure!
Thank you for your detailed response but I am not sure where to begin with all your points. I took couple more pictures with the metal piece attached to the heatsink off(I assume it there to protect the component underneath). It doesn’t seem to be detached or anything, at least not on first glance.
I am not sure if it is the transformer since wouldn’t the problem be on both channels if it was? The buzzing seems to be limited to right channel area. Also I didn’t feel any vibrations when I touched it. If as you said it is coming from the previous stage, where would that be?
Right now I have only a multimeter but I can definetly check if they have a scope in the physics labs at my college. I also looked for signal tracers online and they don’t seem to be that expensive, considering that I want to continue doing things like this, it is not unreasonable to get one. However I would have to teach myself how to use it. As for the microphone, why would I need that for? If it is to pinpoint where the noise is coming from I have a decibel meter that I can use.
What do you think I should start with? Would I benefit from replacing the capacitors and the dual resistor (thanks for explaining that!) just in case?
The dual resistor has a X.C marking on the top and the writing says 5W, 0.15RJX2.
Thanks a bunch!
Thank you for your detailed response but I am not sure where to begin with all your points. I took couple more pictures with the metal piece attached to the heatsink off(I assume it there to protect the component underneath). It doesn’t seem to be detached or anything, at least not on first glance.
I am not sure if it is the transformer since wouldn’t the problem be on both channels if it was? The buzzing seems to be limited to right channel area. Also I didn’t feel any vibrations when I touched it. If as you said it is coming from the previous stage, where would that be?
Right now I have only a multimeter but I can definetly check if they have a scope in the physics labs at my college. I also looked for signal tracers online and they don’t seem to be that expensive, considering that I want to continue doing things like this, it is not unreasonable to get one. However I would have to teach myself how to use it. As for the microphone, why would I need that for? If it is to pinpoint where the noise is coming from I have a decibel meter that I can use.
What do you think I should start with? Would I benefit from replacing the capacitors and the dual resistor (thanks for explaining that!) just in case?
The dual resistor has a X.C marking on the top and the writing says 5W, 0.15RJX2.
Thanks a bunch!
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