Question about Legacy Audio LA770 Car Audio Amplifier

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Can i fix the transistors on my car amp it smokes when i put power to it.

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Stop turning it on, until you change the transistors. you will burn the entire system.

change all the transistor, not only the smoking ones.
check all other components.

Posted on Jun 02, 2010

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1 Answer

No power


For what amp, a Home stereo amp or a car stereo amp? Most car amps will not have internal fuses, but home stereo amps do have internal fuses. You will notice on car audio amps fuses are always plugged into the side of the amps or they have an inline fuse that is on the main power wire into it.
You have more than likely blown a Mosfet Power Transistor, very common in car amps, I'm fixing 3 of them right now with that problem. Class "D" Amps seem to have this problem on a regular basis and they are hard to get working again once they blow. You won't even see any evidence of the bad parts inside the amp either, old amps will fill your car with thick smoke and will have obvious damaged parts. Best bet is you will be looking at buying a new amp unless you paid over $500 dollars for it, it's not worth fixing, check the warranty to have it replaced by the manufacturer.

Apr 02, 2013 | Car Audio & Video

1 Answer

Smoke in the back


If it still works leave it alone and use it as it is. Smoke usually comes from the emitter resistors of the power transistors if they're pushed too hard. Those resistors are about the only electronic devices that still work after you let the magic smoke out.

May 08, 2010 | Samson Servo 300 2-Channel Amplifier

1 Answer

Amp won't power up,anymore! Even with new parts installed,removed


Hiya, dont have a diag either what you will have to try and is compare the left channel with the right. There will be 2 driver transistors (also likely on heatsink) close to the outputs. Check which driver drives which output on the left, then match it on the right. Those same drivers could very well also be a problem on the right as they often go with the outputs. There is a possibilty they have smoked again. See here to test FETS
http://www.4qdtec.com/mostest.html

Basically the left will match the right but not similar locations but definitely by track joins.

Also check the power resistors at the output. Often also go.

Hope that helps

Jul 15, 2009 | Car Audio & Video

1 Answer

T1500-1bd burnt mosfet


First of all is the mosfet your talking about in the output section or in the power supply section? Most car amps use mosfets in the power supply section, some use them in the output section. To test the transistors in your amp, take a digital volt meter and set it to diode check. Then take the leads and put them accross the first and third legs of the transistors. Usally the red test lead on the first leg and black test lead on the third leg of transistor. If you get a reading of 000 then transistor is shorted. If you get a reading below 600 then transistor is on it's way out if not allready or it's next to a shorted transistor that is it's complimentry output transistor. comonly you will have 2 transistors working together, one NPN and one PNP per a channel, or 4 of them in a bridged type output circuit depending on the watts and how man channels your amp has. I was just looking at the specs of this amp and it's got me confused. It says it's a 2 channel but looking at all the info on different pages it says at 4ohm:200wattsx4 and at 2ohms:300wattsx4 and 1 channel mono 600watts into 4ohms. weird for a 2 channel. anyway that is how you test your transistors. Same way for the power supply section but, you will come accross a couple or more switching diodes that look like transistors and you will get a 000 reading when you test those like I specified. They rarely go out and most of the time there is only 2 of them. They will have a diagram like a diode on the front showing you which way the power flows. Let me know what you find out. Your amp should have went to protect mode if you smoked a mosfet.

Feb 08, 2009 | Audiofonics ADF-243 Car Audio Amplifier

1 Answer

Amp wont come on


you might have blown a mosfet transistor or resistor inside the amp

Jan 19, 2009 | AudioBahn A4004T Car Audio Amplifier

1 Answer

Lab l4 bass amp smoked my speakers


Hi,
If your description is to be taken literally, and smoke did indeed come out of the speakers, your output transistors have shorted out, and put the full power supply voltage and current through your speakers.
The amp and the speakers will need to be serviced. The speakers will need new voice coils at the least.

Sep 30, 2008 | Audio Players & Recorders

1 Answer

Legacy 1470 smoke prob.


If it begins to smoke with only the B+, ground and remote connected, the power supply transistors have likely failed.

The protection light generally won't come on if the power supply is blown because the supply must be working for the protection circuit (which protects the output transistors) to engage.

The power light may be connected to the B+ side of the power supply. If that's the case, the power light will illuminate even if the amp is inoperative.

Let me know if you have any other questions.

Aug 27, 2008 | Legacy 4CH 1000W RED AMP Car Audio...

2 Answers

Jl 1000/1 amp not working w7 like it should


If you see smoke, it's virtually always the power supply transistors. There are several things that can cause it but sometimes, they simply fail. I will generally work with people who want to repair their own amplifiers but the this JL amplifier is complex and not always an easy amplifier to repair.

If you can't find a local repair shop to repair it, you'll have to go through an authorized JL retailer to have it repaired by JL.

Let me know if you have any other questions.

Jul 26, 2008 | Jl Audio 1000/1 Car Audio Amplifier

1 Answer

Shorted out amp!


sound like you could have shorted out your audio o/p transistors. if you take the amp apart you should find 1 row on each side of the amp, one side is power & the other is usually for your sound out. the transistors on the audio side out could be bad, look closly to see if they are bubbled,cracked or just dont looke in as good shap like the others. these audio transistors work in pairs, so replace them in pars even if only 1 is bad. if they all look ok, test them with a multi meter to see if they are shorted. good luck.

Nov 08, 2006 | Kicker IX1302 Car Audio Amplifier

2 Answers

Smoking Amp/Fuse Blowing


Sounds like you may have a shorted switching Transistor in the switch mode power supply causing a short to ground. If you are technical enough. Remove power remove cover and do a continuity test on the transistors on the heatsink. non of them should read zero resistance between the three legs. in all connection configuration you use to hook up your meter. If one or Two or even all of them do you must replace with proper part.

Aug 02, 2006 | Legacy LA838 Car Audio Amplifier

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