This is a long post for the sake of being thorough, TLDR posted at bottom.
Hello all! My name is Chris, been lurking here for awhile for tips, tricks, and techniques. Unfortunately I stumbled upon a project now that is possibly out of my depth but want to still rise to the challenge and try to do what I can and hopefully use the knowledge in future projects. I have basic tools and a DMM at my disposal along with basic knowledge on how to use em. My knowledge of proper test techniques and correct terminology may be lacking at times but bear with me as I am willing to give a shot and try! Now onto our test subject.
Initial problem and repair attempt:
I got a hold of a FSR12BV servo subwoofer. Upon applying power it would generate a low hum that got progressively louder until it started to make popping noises. Poked around a bit and my guessing was capacitors due to the age of the unit(almost as old as I am!). Using an ESR meter I have on hand I found that C11, C17, C24, C33; all 10uf@50v to be suspects. Pulled them out and tried to get resistances and capacitance checks on my DMM. Reads as open and no charge up. Replaced them all with the same values. Closed it up, lo and behold it fired up with no hum. Applied a line in signal and its generating sound.
However I noticed at lower frequencies, 20-25hz, and with mid to high volume applied the subwoofer would rattle/distort. It would go away if I turned down the volume on the amp plate. Higher frequencies seemed to play find even at max on the volume dial. To my understanding this was clipping. And from what I read of clipping it was the amp not being able to deliver sufficient power to the sub to drive it properly so it clips the signal leading to the distortion.
Current problem and additional repair attempt:
I should of just left it alone, but curiosity got the better of me. I opened it up again and was just poking around. I changed C40(470uf@16v) and C57(4.7uf@50v) just cause they were in the general same area. I was at a loss of what else I could do so I closed it back up. Fired it up and got a hum this time. Few seconds later it popped, and now I'm just left with a low hum. It won't play sound from a line in signal.
So opened it up, disconnected from the driver and applied power with it sitting on the bench. I see spark and smoke. Upon inspecting I feel the damage may have originated from left over flux that I didn't clean all the way. So now there is a singed area on the underside section of the PCB. About where C60 is. I cleaned as best as I could and applied power again. No fire this time, but the hum is there and originated from either the large block(I guess this is the transformer?) or the power supply section I was working on. I still get +/-45v from the large caps, +/-12 from U5 and U9 transitors. I see 5v from VCC of U13. Anything else would be complete stabs in the dark as I have little knowledge of testing ICs nor the STK properly. Any further help or direction would be greatly appreciated here. Schematics provided by Velodyne attached.
TLDR: Subwoofer hummed and popped. Changed out 4x 10uf@50v caps and the problem went away. However playing lower frequencies at mid-high volumes caused the unit to clip. Tried changing more caps and unit hummed, popped, and sizzled. Need help in direction and troubleshooting from here. Schematics provided by Velodyne attached.
I thank anyone who took the time to read this post and any input be appreciated. Even if is to scold me for doing something stupid, please point it out to me in layman's terms so I can avoid it in the future. I will probably end up cross posting this on different forums just to have more responses. Have a nice day!
Hello all! My name is Chris, been lurking here for awhile for tips, tricks, and techniques. Unfortunately I stumbled upon a project now that is possibly out of my depth but want to still rise to the challenge and try to do what I can and hopefully use the knowledge in future projects. I have basic tools and a DMM at my disposal along with basic knowledge on how to use em. My knowledge of proper test techniques and correct terminology may be lacking at times but bear with me as I am willing to give a shot and try! Now onto our test subject.
Initial problem and repair attempt:
I got a hold of a FSR12BV servo subwoofer. Upon applying power it would generate a low hum that got progressively louder until it started to make popping noises. Poked around a bit and my guessing was capacitors due to the age of the unit(almost as old as I am!). Using an ESR meter I have on hand I found that C11, C17, C24, C33; all 10uf@50v to be suspects. Pulled them out and tried to get resistances and capacitance checks on my DMM. Reads as open and no charge up. Replaced them all with the same values. Closed it up, lo and behold it fired up with no hum. Applied a line in signal and its generating sound.
However I noticed at lower frequencies, 20-25hz, and with mid to high volume applied the subwoofer would rattle/distort. It would go away if I turned down the volume on the amp plate. Higher frequencies seemed to play find even at max on the volume dial. To my understanding this was clipping. And from what I read of clipping it was the amp not being able to deliver sufficient power to the sub to drive it properly so it clips the signal leading to the distortion.
Current problem and additional repair attempt:
I should of just left it alone, but curiosity got the better of me. I opened it up again and was just poking around. I changed C40(470uf@16v) and C57(4.7uf@50v) just cause they were in the general same area. I was at a loss of what else I could do so I closed it back up. Fired it up and got a hum this time. Few seconds later it popped, and now I'm just left with a low hum. It won't play sound from a line in signal.
So opened it up, disconnected from the driver and applied power with it sitting on the bench. I see spark and smoke. Upon inspecting I feel the damage may have originated from left over flux that I didn't clean all the way. So now there is a singed area on the underside section of the PCB. About where C60 is. I cleaned as best as I could and applied power again. No fire this time, but the hum is there and originated from either the large block(I guess this is the transformer?) or the power supply section I was working on. I still get +/-45v from the large caps, +/-12 from U5 and U9 transitors. I see 5v from VCC of U13. Anything else would be complete stabs in the dark as I have little knowledge of testing ICs nor the STK properly. Any further help or direction would be greatly appreciated here. Schematics provided by Velodyne attached.
TLDR: Subwoofer hummed and popped. Changed out 4x 10uf@50v caps and the problem went away. However playing lower frequencies at mid-high volumes caused the unit to clip. Tried changing more caps and unit hummed, popped, and sizzled. Need help in direction and troubleshooting from here. Schematics provided by Velodyne attached.
I thank anyone who took the time to read this post and any input be appreciated. Even if is to scold me for doing something stupid, please point it out to me in layman's terms so I can avoid it in the future. I will probably end up cross posting this on different forums just to have more responses. Have a nice day!
I'd say nothing you did, you just got a broken unit to begin with. The behavior at turn on sounds like a run-away condition, perhaps they do this when the servo has no feedback from the accelerometer that's supposed to be sending a signal from the woofer cone.
Your only fault was allowing your curiosity to turn it on a second time, before studying the matter a little better. This happens to all of us. Who knows how long it would have take to recognize the accelerometer signal issue? Now that it really is toast, I'd have a look at where the accel is and if it's doing what it's supposed to do. That might require a 'scope, as you'd have to tap the cone and see if you can see a transient signal at the output of the accel amplifier.
Your only fault was allowing your curiosity to turn it on a second time, before studying the matter a little better. This happens to all of us. Who knows how long it would have take to recognize the accelerometer signal issue? Now that it really is toast, I'd have a look at where the accel is and if it's doing what it's supposed to do. That might require a 'scope, as you'd have to tap the cone and see if you can see a transient signal at the output of the accel amplifier.
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