Home theater geeks: Why is the internal fuse blowing on my subwoofer's amplifier? - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 05-10-2008, 09:08 PM   #1 (permalink)
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Home theater geeks: Why is the internal fuse blowing on my subwoofer's amplifier?

So I clicked on the home stereo today and noticed the sound was kinda weak, specifically, there was no bass. I had a little time, so I chased the rats nest of wires behind the stereo / tv / dvd / stereo and after some dumbass diagnosis figured out that the sub (which has its own amp on the back), didn't have any power. I fished out the sub from behind the rat's nest o' crap and plugged it into a known working outlet. Ziltch, nada, according to the green idiot light that's supposed to illuminate when it's on. Thinking the idot light may have gone south, I try several other things and eventually come to the conclusion the amp is dead as a hammer.

At this point it became a mission to find out wtf, so I ignored all the 'shock hazard' warnings and pulled the back off the amp, which is mounted behind the sub's cabinet. And whaddaya know, there's a glass fuse that's obviously cooked on the circuit board attached to the transformer. 125v, 2.5 amp, and two stickers warn to replace with same. No biggie, go to Radio Shack, get replacement fuses (marked 250v, 2.5 amp), 4-pack, $3.50, and I walk away thinking how stupid it would have been to throw the sub away for a 50 cent fuse. Pop-in new fuse, plug-in, immediately the fuse pops. The power button was on when I plugged it in, so this time I turn it off, replace with another fuse, leave the back off the amp so I can see what happens, push the power button and am briefy blinded by a white-blue flash as fuse number 2 meets its maker. WTF?

Looked online and found a place that said 125v fuses and 250v fuses can be used interchangeably as fuses don't really care what voltage, only amperage, which makes sense I guess. Is this true? I could go bigger on the fuse but I'd rather not burn the house down...seems like they usually know what they're talking about when rating fuses.

Is there something else to check? I have a multi-meter and am not afraid to use it. I recall paying around 200 bucks for this thing a couple years ago and know I could just replace it, but it's a nice Sony unit and worked bitchin'. Any electronic tech out there want to shed some light, or do I just trash the thing?
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Old 05-10-2008, 09:51 PM   #2 (permalink)
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So I clicked on the home stereo today and noticed the sound was kinda weak, specifically, there was no bass. I had a little time, so I chased the rats nest of wires behind the stereo / tv / dvd / stereo and after some dumbass diagnosis figured out that the sub (which has its own amp on the back), didn't have any power. I fished out the sub from behind the rat's nest o' crap and plugged it into a known working outlet. Ziltch, nada, according to the green idiot light that's supposed to illuminate when it's on. Thinking the idot light may have gone south, I try several other things and eventually come to the conclusion the amp is dead as a hammer.

At this point it became a mission to find out wtf, so I ignored all the 'shock hazard' warnings and pulled the back off the amp, which is mounted behind the sub's cabinet. And whaddaya know, there's a glass fuse that's obviously cooked on the circuit board attached to the transformer. 125v, 2.5 amp, and two stickers warn to replace with same. No biggie, go to Radio Shack, get replacement fuses (marked 250v, 2.5 amp), 4-pack, $3.50, and I walk away thinking how stupid it would have been to throw the sub away for a 50 cent fuse. Pop-in new fuse, plug-in, immediately the fuse pops. The power button was on when I plugged it in, so this time I turn it off, replace with another fuse, leave the back off the amp so I can see what happens, push the power button and am briefy blinded by a white-blue flash as fuse number 2 meets its maker. WTF?

Looked online and found a place that said 125v fuses and 250v fuses can be used interchangeably as fuses don't really care what voltage, only amperage, which makes sense I guess. Is this true? I could go bigger on the fuse but I'd rather not burn the house down...seems like they usually know what they're talking about when rating fuses.

Is there something else to check? I have a multi-meter and am not afraid to use it. I recall paying around 200 bucks for this thing a couple years ago and know I could just replace it, but it's a nice Sony unit and worked bitchin'. Any electronic tech out there want to shed some light, or do I just trash the thing?
Not a guru, but, did you look at the circuit board to see if any of the soldier traces are burnt? How about disconnecting the output to the woofer and any other wiring other than the power input and trying another fuse.

There is obviously a more than factory rated power draw as you know. Check continuity on the woofer itself and any wiring you can reach that is connected. I wouldn't spend more than the original price in labor (at whatever you make per hour) trying to fix it.
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Old 05-10-2008, 09:55 PM   #3 (permalink)
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A blown fuse 99.999% of the time means something is toasted inside, throwing a new fuse in usually doesn't fix anything. Take a look at the boards to see what's burnt. Have you had any bad weather, lightening or power surges lately?
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Old 05-10-2008, 11:56 PM   #4 (permalink)
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A blown fuse 99.999% of the time means something is toasted inside, throwing a new fuse in usually doesn't fix anything. Take a look at the boards to see what's burnt. Have you had any bad weather, lightening or power surges lately?
Without unscrewing the boards from their home I really don't see anything wrong on the inside; the power board is easy to see and there's nothing obviously wrong in terms of burnt tracers or whatever on the board. I moved not long ago and as embarrassing as it is to admit, I think the thing may not have been working since the move. Nothing in terms of outages or weather or anything. The transformer, fuse holder, power in, and related board is readily accessible, anything else I could check other than burned tracers on the board?
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Old 05-11-2008, 12:02 AM   #5 (permalink)
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Without unscrewing the boards from their home I really don't see anything wrong on the inside; the power board is easy to see and there's nothing obviously wrong in terms of burnt tracers or whatever on the board. I moved not long ago and as embarrassing as it is to admit, I think the thing may not have been working since the move. Nothing in terms of outages or weather or anything. The transformer, fuse holder, power in, and related board is readily accessible, anything else I could check other than burned tracers on the board?
Transistors.
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Old 05-11-2008, 12:19 AM   #6 (permalink)
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Transistors.
Care to elaborate? I have wired a few Jeeps, am not an electronics tech, but have soldering gun and know how to use it. Multi-meter too. Or should I let this go?
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Old 05-11-2008, 12:26 AM   #7 (permalink)
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Care to elaborate? I have wired a few Jeeps, am not an electronics tech, but have soldering gun and know how to use it. Multi-meter too. Or should I let this go?
Unless you have a soldier station, or know someone that does, removing and reinstalling transistors, caps, or anything else on the board is a waist of time for the average Joe! By the time a standard soldiering gun heats up enough to melt the joint, you run the risk of the trace runs.

Go buy a new one and crank it up again.
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Old 05-11-2008, 12:44 AM   #8 (permalink)
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Care to elaborate? I have wired a few Jeeps, am not an electronics tech, but have soldering gun and know how to use it. Multi-meter too. Or should I let this go?
It's not a difficult test with a meter no. Do you recall the sub brand off hand?
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Old 05-11-2008, 08:55 AM   #9 (permalink)
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Troubleshooting instructions. This technique will positively isolate the defective component that is causing the fuse to blow.

1. Turn power switch to the "OFF" position.

2. Replace fuse with a piece of " copper tube.

3. Point video camera at amplifier. Start recording.

4. Using a long stick, turn power switch to "ON" position.

5. At this point, the defective component should commit suicide in a spectacular manner.

6. Turn off video camera. Post video on PBB.

7. Go to Best Buy and purchase new amplifier.
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Old 05-11-2008, 09:56 AM   #10 (permalink)
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Quote:
Originally Posted by Rockcrusher View Post
Troubleshooting instructions. This technique will positively isolate the defective component that is causing the fuse to blow.

1. Turn power switch to the "OFF" position.

2. Replace fuse with a piece of " copper tube.

3. Point video camera at amplifier. Start recording.

4. Using a long stick, turn power switch to "ON" position.

5. At this point, the defective component should commit suicide in a spectacular manner.

6. Turn off video camera. Post video on PBB.

7. Go to Best Buy and purchase new amplifier.


Dooooo ittttttttt
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Old 05-11-2008, 01:33 PM   #11 (permalink)
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A blown fuse 99.999% of the time means something is toasted inside, throwing a new fuse in usually doesn't fix anything.
You would be surprised how many people just cannot grasp this concept.

A long time ago, I worked at Radio Shack. At least once a week someone would come in trying to return a box of blown fuses saying that they were defective because "every time I stuck one in it would immediately blow out"
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Old 05-11-2008, 01:43 PM   #12 (permalink)
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Quote:
Originally Posted by Rockcrusher View Post
Troubleshooting instructions. This technique will positively isolate the defective component that is causing the fuse to blow.

1. Turn power switch to the "OFF" position.

2. Replace fuse with a piece of " copper tube.

3. Point video camera at amplifier. Start recording.

4. Using a long stick, turn power switch to "ON" position.

5. At this point, the defective component should commit suicide in a spectacular manner.

6. Turn off video camera. Post video on PBB.

7. Go to Best Buy and purchase new amplifier.
YES! Doo it! Hell splice a dryer cord on that thing.
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Old 05-11-2008, 01:58 PM   #13 (permalink)
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If you don't know what to look for, you likely wont succeed.

Give it the deep six, but first, follow 'crusher's troublemaking procedure.
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Old 05-11-2008, 04:23 PM   #14 (permalink)
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If you don't know what to look for, you likely wont succeed.

Give it the deep six, but first, follow 'crusher's troublemaking procedure.
I figured as much. Ciruit City has a new one for a hundred bucks so that's where I'm headed.

I would follow Rockcrusher's instructions but I'm a loser that doesn't own a video camera. I can say that staring directly at the fuse when I turned on the power did produce a very impressive flash that made me see spots for a few minutes.

Thanks for the input, guys.
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