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 Post subject: did I blow my Amp
PostPosted: Mon Jan 15, 2018 3:26 pm 
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Joined: Thu Aug 01, 2002 12:01 am
Posts: 2802
Location: San Jose CA
I was working with an Alpine 2 channel car amp and trying to bridge outputs to a dual voice coil subwoofer. 4 ohms x2
Initially I got some output putting each coil on Left and Right but that's not a proper hookup. next step I paralleled the VC to obtain 2 ohms impedance and placed it across (what I thought were) the outer two (Left - and R +) but maybe I did it wrong, could have bridged any two terminals for a short time. (nothing was on for more than a minute or two in any config).

In any case, I don't get any output now and nothing inside looks fried. I'm using a digital monobloc amp for the sub now and that works so the speaker is unharmed.

https://pdf.crutchfieldonline.com/Image ... RPF240.PDF

Found and added this to post
https://www.manualslib.com/manual/95472 ... e=8#manual

Mostly I'm just asking if anyone Knows that this is a known way to blow an amp.


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 Post subject: Re: did I blow my Amp
PostPosted: Mon Jan 15, 2018 6:04 pm 
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Joined: Fri Feb 01, 2002 1:01 am
Posts: 1754
Location: Mideast USA
Hi. Did you connect it this way ? Being the speaker symbols actually coils of the same subwoofer ?
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You are a skilled non-beginner... Let's fix it. Power supply rails fine, right ?
Warm up the scope...



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 Post subject: Re: did I blow my Amp
PostPosted: Tue Jan 16, 2018 5:15 pm 
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Posts: 2802
Location: San Jose CA
I agree it is repairable, I need to take it out of the car and put together a bench setup with some signal sources first. I've had these sitting on a shelf for nearly a decade and now I am completely refurbishing my 93 Explorer and these fit well under the seats. (they were insurance replacements for 2 that were stolen). That was a fun project now basically So I need to take a closer look at the whole setup, since there seems to be no output at all, not scratchy or low. I can use a scope but probably start with AC RMS measurements.done.

I studied the schematic some more, I don't think one can blow the output with an incorrect bridged hookup, I would have either one channel or ground on both sides or reverse phase because the negative speaker terminals are all common ground.



Can't see any of the ICs when I look inside, they must be on the hidden backside of the PCB and need some disassembly. The service manual does not show that side of the PCB either. its a mystery until I tear it down but not until after basic diagnostics.

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 Post subject: Re: did I blow my Amp
PostPosted: Tue Jan 16, 2018 5:31 pm 
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Joined: Sat Nov 08, 2003 1:01 am
Posts: 1589
Location: Phoenixville, PA USA
Hate to be the one to say this, but, most of those amps have a fuse. Is it good?

Addendum
I see the main fuse up by the transformer. I'm sure you checked it, but gotta rule it out.



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 Post subject: Re: did I blow my Amp
PostPosted: Tue Jan 16, 2018 9:11 pm 
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Joined: Sat Nov 08, 2003 1:01 am
Posts: 1589
Location: Phoenixville, PA USA
Next question.

You don't have the MUTE activated somehow, do you?



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 Post subject: Re: did I blow my Amp
PostPosted: Wed Jan 17, 2018 8:53 pm 
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Location: San Jose CA
Not the fuse. Initially I didn't check because the pilot lamp was turning on and off with the remote switch as expected but than I worried there might be a current path to the LED without power but although there is, the resistance is too high to light the lamp. I checked it today and was good. Mute and remote are basically the same thing external to the amp.


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 Post subject: Re: did I blow my Amp
PostPosted: Thu Jan 18, 2018 7:09 am 
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Joined: Fri Feb 08, 2002 1:01 am
Posts: 4250
Location: USA / North Carolina / Fayetteville
your outputs are the 4 big mosfets on the left, on the right is your power mosfets and diodes for the power supply.
is there not a PROTECT led lit up ?

here is how you properly bridge a car amp.. left and right input as normal.. then follow this...

https://www.wikihow.com/Bridge-an-Amplifier

what is the model and name of the amp you have ?


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