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Old 24th August 2012, 03:08 PM   #1
nmasino is offline nmasino  United States
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Default amp causing low voltage reading

I have a brand new BOSS AR1200.2 amp and am having issues with it not turning on. At first it was working, powering up and driving my two sub woofers. When you'd turn up the volume to a decent level it would shut off. I'm assuming the protection went on. Now, the power and protection LEDs will not even turn on. I put a volt meter on my battery and alternator and it reading 14.5 volts. When I put it on the power lead that goes on the amp when disconnected from the amp it reads about 14.5 as well. When connected to the amp, it reads 1.9-2 volts. Why does the voltage read so low when connected? This unit is brand new, and now it doesn't work. When I run these tests, I have NO speaker wires hooked to the amp, just a very good ground, remote (reads about 14v) and power, B+. The speaker box has 2 sub woofers, and am not bridging any of the speakers, a pretty basic setup. But again, the speaker wires are completely disconnected and am still getting a low voltage reading.
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Old 24th August 2012, 07:12 PM   #2
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Sound like you blew up some/all of the switching mosfets, They are on the primary side of the step up transformer. Or, I think there is a large diode that goes accross the +/- 12v input, I think it for reversal protection. IMO...
What size wire do you have going to the Batt and your ground should be short in lenght and of the same heavy gage.
I've seen amp cook that have a bad ground not large enough wire going to the Batt/Ground.
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Old 24th August 2012, 07:40 PM   #3
nmasino is offline nmasino  United States
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The ground and B+ cables are the same gauge, I don't know the exact number but they are from an install kit and about the thickness of a cable tv cable. I used them for years on my other car, so I believe they are good enough to power the car. The ground is drilled and screwed into the sheet metal in the trunk and is also clean with open metal. I was really careful not to hook up anything incorrectly, including disconnecting the battery when I was hooking it up.

When I would turn up the volume, the amp would cut out. It did this a few times and then it wouldn't go back on. I'll just send it back on warranty, unless anyone has any other ideas.
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Old 24th August 2012, 08:20 PM   #4
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OK, Hopefully its 8g or better (4g is common for that much power). You don't want to try to push an ocean through a garden hose.
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Old 24th August 2012, 08:33 PM   #5
nmasino is offline nmasino  United States
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...I have 3 more amps with the same voltage symptoms, all eventually going out some time in the past 15 years. Most lasted at least 3-5 years though. This one just did it right away.
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Old 24th August 2012, 09:37 PM   #6
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HHMMM... Are you driving them too hard? If its a sub amp, it hard to hear the amp clipping. Did you notice if they got hot while playing music hard?
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Old 24th August 2012, 10:16 PM   #7
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if the power wire drops voltage that bad with the amp hooked up, and the remote still reads 14v with the neg. probe on the ground input attached to the amp, then there is a problem in your power wire. check the power going in and out of the fuse. it is common for a fuse to break connection inside, where you cannot see. this, is especially if you are trying to run too much power through the wire, because the wire will heat. 8awg is only good for 4-500rms amps. 4awg is good for the 6-1k range. read the charts and power requirements for your amps and wire/fuse accordingly. first-hand, 9/10 times this issue is simply the battery connection or fuse. also, a voltage problem like this, will only kill your amp, as you should have learned 3x over. x2 on not pushing your amps harder that what they will really put out.

... so, what is the fusing on the amp itself (or suggested fusing in the manual) and is it more than your 8awg or less can handle@ length? (google awg ampacity chart, if it is not shown in your manual)
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Old 24th August 2012, 11:40 PM   #8
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Agree
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Old 25th August 2012, 02:18 AM   #9
nmasino is offline nmasino  United States
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Thanks guys, this is great information.

No, I don't 'think' I'm driving them that hard. This new one, I barely turned up the input level to around 4db's and it cuts out. It kept doing it and now it's toast.

The fuse that came with the amp is 35amps, and the manual confirms this is correct. It wasn't broke, but I saw on bcae1.com that the internal could break without seeing it so I replaced it and had the same results. The other amp's I've owned only use 20amp fuses.

I believe the wire is a cheapo 8ga from a kit I picked up at Fry's in Downers Grove, IL back in 2005. I had my last amp hooked up to that for 5 years until it shorted out from water getting into the trunk. The cable may be the issue though and I'll upgrade the it and see if that fixes my problem before sending the amp out on warranty. But it sounds like the transistors may be shorted out anyways. I'm checking out the ampacity tables now...

I took the covers off of two of my old amp's and did the appropriate transistor tests on bcae1.com and they are toast. On one of the amps I was able to find all the transistors on digi-key.com and it was only $13 so I ordered them. This is my first time messing with amp electronics, so if I fix it - great, if not no real loss.

This is a great site, many interesting posts so far. I have an old Crate amp that went out on my years ago so I may try taking a look at that too.
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Old 25th August 2012, 06:16 AM   #10
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what amps do you have? with 35a of fusing, then you are not going to overload 8awg.
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