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Shorted car audio amplifier

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dnolan747

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Hi my name is Dean and I am the owner of 747 Electronics and CB,, and I have on the bench a Power Acoustik TS980-2 with a dead short from 12v positive to ground,,, I dont repair many car audio amplifiers so plz. bare with me...

Customer said that it blows fuses as soon as they are installed so I put 2 new fuses inline without power and checked continuity between positive and negative hookups and yes there is a dead short,,, so I was thinking it was hooked up backwards and blew the reverse polarity diode,, the diode in circuit showed short but when I removed it from the circuit it checked good,, so next I figured shorted power transistor so I pulled each and every one of them and all checked good with a transistor checker... even checked the 2 triodes and they checked good out of circuit...

I am pretty much lost now and am needing some advice

Thanks

Dean A Nolan
747 Electronics and CB
 
Hi denolan

It all depends on what kind of short you have. Do you have a flat short or a delay short? If you have a flat short look for a bad Fet from S to G, S to D. or perhaps could be a bad driver, rectifier or the tl494 in most cases.

A delay short could be a bad output or driver.

Always use a shunt R and a small psu to fire up Amp. This will avoid further trouble.
 
already had this type of trouble with subwoofer car amp it is almost always the mosfet at input that are blown. Remove them one by one and you should found the responsible or change them all
 
Thanks guys for the replies,, This one is kicking my butt, but I guess it is good experience,,,

As stated earlier I have checked all power transistors and driver transistors the are bolted to the heat sink and all of them check good with a transistor checker... I guess I will have to next check rectifiers and regulators and this tl494...

Leal can you plz explain the difference between a flat short and a delay short????

Thanks guys

Dean
 
Ok,

what I mean by a flat short is that you will get an instant short, just by applying the pwr lead to the terminal pwr post.

On a delay short you will apply pwr, but it will take a few seconds to kick in and if you have a bad output,driver or component it will start drawing current. (In most casses); This is why you should use a shunt R.
 
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It is rare, but possible for an electrolytic capacitor to go shorted too.
I would start pulling parts off the 12v rail and each time check for a short.
Most likely it is a shorted mosfet.

-Ben
 
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