Amp Shorted Out

[rich21]

i finally figured out what kept on blowing my fuse and its the amp. in a nakamichi amp what would most likely short out? i took it apart and im guessing i was looking at the output which would be a row of ten black squares or boxes. 2 big ones and 8 small ones. on the small ones theres one with a little hole. can that be apossibility of the short?

[rich21]

no one knows huh... :(

[rich21]

my back speakers didn't work so i got aftermarket speakers and put them in, but before that the sound on my radio kept going out every now and then. i put the speakers in, it worked for a week and then one morning i turned it on and nothing. no power nothing. my amp shorted out. do you think the new speakers finished the amp off.

[Sluggo]

If there is a "hole" in one of the black "boxes", then you probably have found the source of your problem. The "boxes" are the output transistors for the individual amplifiers in your multichannel amp.

A "hole" is caused when the transistor die get so hot that it literally blows the plastic packaging material (the black stuff) out, leaving a little crater. The transistor probably got hot because it failed (shorted) internally, and so the +14.4 Volt supply got shorted to ground. This allows a buttload of current through the device, heating it up to the point that it blew out the packaging.

The failed transistor probably remains shorted, and this is why you are blowing fuses. Remove that transistor from the amp, or simply cut it's leads so that it has no electrical connection to the circuit.

New speakers, if they were of a lower impedance then the old speakers, may have caused the overheating of a weakened transistor.

[VincyRay]

Does anyone know anything about replacing the factory Pioneer amp w/ an aftermarket? Can you do it, or would you have to replace the entire unit?

[rich21]

if i were to take out the blown transistor will the amp then work and will i have sound from my radio? also what do you mean "if they were of a lower impedance then the old speakers?"

[Sluggo]

if i were to take out the blown transistor will the amp then work and will i have sound from my radio? also what do you mean "if they were of a lower impedance then the old speakers?"

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I would take the blown transistor out and plug the amp back in - you have nothing to lose but another fuse. Each channel's amplifier is isolated from the others, so the blown channel will definitely not work, but the others might. You don't have to unsloder the blown transistor, just cut the three leads (wires) which enter the body of the transistor.

Lower impedance = fewer ohms = greater load on the amp. For instance, if you took out some 4 Ohm speakers and put in some 2 Ohm speakers, then the amp would have to deliver twice the current at the same volume control seting. The increased current means more heat in your amp and may mean an overloaded output transistor. Thus the hole.

[rich21]

cooooooooooooooooooooooooooooooooooooooooooooool... im gonna cut the threads. i'll let you know know what happens. thanks for helping out.

[rich21]

Sluggo, you do not know how i feel right now. you were right and now i have a radio. :D the only speaker that doesn't work is the sub, but im just so happy that the radio works. the sub i deal with it later. i appreciate the time you took to explain what it was and how to handle the problem. where can i go to get a transistor to replace the blown one? again thanks so much.

[Sluggo]

Great news Rich, glad to hear it worked! And pour yourself one, it was you who noticed the transistor with the hole in it.

As far as replacing it ... that may be another story. Typically these things do not just "blow", but are damaged due to something else being "wrong". You will want to confirm that whatever that channel was connected to is not damaged in some way.

Measure the subwoofer with an Ohmmeter to make sure it's not shorted, or simply take it to a local car stereo shop and have them test it. If it measures okay (4-6 Ohms), then you could replace the broken device. Have a real repair shop do the work, as opposed to a stereo installer.

If the sub measures less than 2 Ohms, it will cause problems. Get it replaced first, then test the new sub with the repaired amp. There's no way to repair a shorted loudspeaker - it would require a new voicecoil, and a new sub will be far cheaper than trying to fix the old one. If you need a new sub, I'm told this:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...ssPageName=WD1V

is a drop-in replacement, but the mounting depth of 5.5" seems like it might be too much.

[rich21]

thanks again Sluggo. extremely happy. i've gone without a radio for a while. no more silence for me.