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bmsgaffer86 05-31-2007 03:47 PM

Help, smoke! Fixed once. New Pictures!
 
3 Attachment(s)
OK so lets start off with a background.
I have two amps in my car a 4 channel
alpine for the interior speakers and a mono
Bazooka for the sub. I got the bazooka for
$50 off of a friend. I also recently aquired a
HAM radio that you may have seen in my previous post.

So the first time i try to transmit (50w out) on my
new radio i hear BOOM. I think nothing of it because
it never happened again. Until i get to school and find
my trunk is filled with smoke. Upon pulling every fuse
i could find i found it was my mono bazooka that was
blowing fuses and so i took it out and dissasembled it
to find this.

Attachment 47655

Attachment 47656

Attachment 47657

Now, the antenna wire for my ham rig goes
right by the input lines for both amplifiers, could
it possibly be that the leakage from that line caused
enough current in the low voltage line to destroy the
cheap amplifier, but not the alpine?

Anyone have any idea what these particular rectifiers do in this amp?

I can buy them online, if i replace them would it work?

How do i protect them in the future?


Anyone with any ideas or even stupid comments are welcome to reply.

sandness 05-31-2007 04:14 PM

Those are the MOSFETs that are toasted. $1.69 a pop http://www.mouser.com/search/Product...key844-IRFZ46N
Worth a shot if you feel handy with the soldering iron. But with the extent of the burn marks, some of your traces may be shot. From the pics, the caps and resistors I see appear fine. I'd give it a shot.

Are you running good quality shielded cables from your source to the amps? If not, they could have picked up some RF. I would definitely move the antenna line away from the inputs regardless. Was the stereo on at the time?

On a side note, why are you running a ham radio in your car? Just for kicks?

bmsgaffer86 05-31-2007 04:24 PM

Quote:

Originally Posted by sandness
Those are the MOSFETs that are toasted. $1.69 a pop http://www.mouser.com/search/Product...key844-IRFZ46N
Worth a shot if you feel handy with the soldering iron. But with the extent of the burn marks, some of your traces may be shot. From the pics, the caps and resistors I see appear fine. I'd give it a shot.

Are you running good quality shielded cables from your source to the amps? If not, they could have picked up some RF. I would definitely move the antenna line away from the inputs regardless. Was the stereo on at the time?

On a side note, why are you running a ham radio in your car? Just for kicks?


Haha, i knew they were MOSFET's but i was reading International Rectifier's datasheet at the time and my mind played tricks on me. I just wasnt sure if i was looking at pre-amp mosfets or the finals or what.

The top traces seem fine, and all the bottom ones are covered pretty thick with solder so they look like they can handle well over the 35 amps my fuse was rated at.

Now that you mention it, my mono-amp's RCA cable runs only from one amp to the next (right next to eachother) and its probably just a cheapo one i had laying around.
And yes, the stereo was on at the time, albeit not playing aything cause i had my computer paused.

Its a 2 meter/ 70 cm mobile radio. I use it to talk to people on the local repeaters and talk to my buddies when were on long drives. Its great cause theres thousands of chanels compared to FRS's 20ish channels and i can probably hit at least 25-30 miles on just the power from my mobile. So it kinda smears the non-license radios into the ground.

Im an EE student, so im great at soldering big things like this. Still need a bit of practice on the SMT parts.

Bugsi 06-02-2007 10:53 PM

Graduate of EE school and reformed amplifier repair technician chiming in here. . .

Those typically blow like that when the output is short circuited. So if you're going to give repair a go (I would), please check whatever you had the output of that connected to BEFORE you hook it back up.

I'd give heavy odds that either your output wiring was short circuited, or the sub (or whatever speaker it was driving) is shorted at the coil.

Also, that white pad behind the heatsink/mounting tabs of the mosfets is also an electrical insulator, so make sure you don't have a burned spot on it or some other damage where the tab on the new mosfet could physically touch the metal of the heatsink that it is mounted to. If necessary, get some replacement insulator material at rat-shack or other place. You don't have to use the exact same material, it's okay if you use the clear mica insulator stuff instead, but just make sure it's all mounted correctly and insulated properly.

Oh, and replace all four of those. Don't even try replacing just the two burned ones. Do all four or nothing.

What model amp is that?

bmsgaffer86 06-03-2007 01:22 AM

Quote:

Originally Posted by Bugsi
Graduate of EE school and reformed amplifier repair technician chiming in here. . .

Those typically blow like that when the output is short circuited. So if you're going to give repair a go (I would), please check whatever you had the output of that connected to BEFORE you hook it back up.

I'd give heavy odds that either your output wiring was short circuited, or the sub (or whatever speaker it was driving) is shorted at the coil.

Also, that white pad behind the heatsink/mounting tabs of the mosfets is also an electrical insulator, so make sure you don't have a burned spot on it or some other damage where the tab on the new mosfet could physically touch the metal of the heatsink that it is mounted to. If necessary, get some replacement insulator material at rat-shack or other place. You don't have to use the exact same material, it's okay if you use the clear mica insulator stuff instead, but just make sure it's all mounted correctly and insulated properly.

Oh, and replace all four of those. Don't even try replacing just the two burned ones. Do all four or nothing.

What model amp is that?


Now this is some well received input! I have 5 mosfets ordered, i wasnt going to chance the two good looking ones even based on heat damage. I automatically assumed the radio, and thus the input was at fault, but the subs are a bit under the max power of that amp and the radio did make the system do a nice THUMP, so maybe i fried the sub.


*Taking an ohm meter to the subwoofer right now*

3.4 ohms on a 4 ohm speaker. Sounds acceptable to me, but the wires are a bit scrunched where they were connected so still a possibility.

Another note: the thin, unsheilded signal wire was LOOPED just underneith the antenna wire, so there is a good chance a decent amount of DC voltage could have gone into the low voltage inputs when the 50 watts of RF went above it.

Its a Bazooka ELA500.1

Bugsi 06-03-2007 03:53 AM

I agree that your speaker coil ohms out okay. That leaves the speaker wiring from the amp to the speaker as the most likely cause of a short that blew those mosfets. And really, a short circuit on the output is almost required to blow those things, so when you wire it up again, make double-dog-dare certain that your wiring is good, and check it with a meter to make certain. Even a stray frayed cable thread can do it.

But I'd say you have good odds of getting this amp back up and running if you replace those mosfets.

Keep us informed!

bmsgaffer86 06-27-2007 01:54 AM

6 Attachment(s)
SO

I got the amplifier repaired. It worked GREAT. I was so happy i couldnt believe it. It went that way for a week or more. I figgured, heck it MUST have been a short of the speakers wires cause i was using my ham radio and everything.

Then one afternoon i transmitted on my ham radio right after powering it up, at full power and BOOM no bass. FUDGENUTS i thought as I saw my headlights dim severely before 60 amps of fuse blew.

So lesson learned- dont transmit full power on initial radio-power up with a cheap amp anywhere nearby. I let the pictures speak for themselves. Keep in mind this worked perfectly for a WEEK or more, so the install went great.

P.S. I have a new record for uninstall of an ampifier - 30 seconds on the side of the freeway with a pair of pliers.

Attachment 46066

Attachment 46067

http://i6.photobucket.com/albums/y21...m/100_2991.jpg

http://i6.photobucket.com/albums/y21...m/100_2994.jpg

Attachment 46068

Attachment 46069

Attachment 46070

Attachment 46071

It started with wisps of white smoke, then since it was a slow blow fuse, black smoke as i went crazy so my car didnt burn down. Only first degree burns on my palm but the car is perfect... besides a small stench.

bmsgaffer86 06-27-2007 02:06 AM

If anyone feels sorry for me and wants to help out: :lol:

http://www.bonnevilleclub.com/forum/...ic.php?t=80783

Bugsi 06-27-2007 05:04 AM

Wow, that's some crispy critters! I still can't figure how transmitting on a ham radio near the amp would cause the amp to blow. I mean, I don't doubt that it did, but I'd like to know the electrical explanation for it. Somehow that amp sinked some serious power as if it was connecting the battery +12V directly to ground through your amp circuitry. -But WHY??? Unless your ham radio is seriously mis-wired.

I once wired a car radio's ground to a wire that measured ground, but turns out it was the circuit for accessory & dash lighting. -It was grounded when off, and +12V when on. It was +12V when the headlights were turned on, for example.

That blew the radio when I was driving with it on, and flicked the headlights on.

Is it possible your ham radio is miswired maybe to the amp somehow?

bmsgaffer86 06-27-2007 02:28 PM

Well i think we figgured a couple of problems that could have caused this.

First off, I dont think it is a mis-wire because the grounds all go straight to the chassis on both setups and the hots either are straight from battery or fuseblock. And it only occures when i FIRST turn on my ham-radio, and tranmit at full power.

So the first part of the equation is the ham radio. It has some circuit that dumps alot of power somewhere (havent figgured if its in the power wires or from the antenna, latter being the most likely) if the radio is recently powered on and transmitted.

Second part is the subwoofer circuitry. You said that it looks like it is a short on the speaker somewhere to blow those, but what if the unsheilded wires TO the subwoofer or the coil in the sub itself was the reciever in this equation and sent the power back to the amp. Could that spike cause a similar effect? Cause the antenna is on the trunk, so its close but still...

The last option is still the crap RCA input wires, but i kinda put that on the backburner since you said it looked like a short.


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