sirgrantalot

i just bought a precision audio amp off of ebay, its kinda old and used, and one channel is gone

when i hooked it up to my sub, it acted wierd, like it wasnt pushing hardly any watts

it even did this to a little shelf system speaker i had laying around

what could be the problem??
is it something that i can fix?
i have moderate electronics experience

could i fix the channel thats gone??

the amp is 2 channel 400w

sirgrantalot

btw my sub is a super blue 15

Icemark

you would want to post this in the audio/interior section as it is not FC related.

But it sounds like half an output channel is blown in the amp

Fitness Stain

damn.....icemark is a stickler for the proper sections....

THATS JUST A JOKE (a stupid one at that) SO DONT TAKE OFFENSE OR CHEW ME OUT!

=-dustin

Icemark

I didn't take offense... if it really bugged me I would ask to be a moderator just so I cold move stuff like this.

All in fun Justin, but next time he'll know where to post, right???

Fitness Stain

all is fun....
and its dustin

Icemark

Whooopssss.....That will teach me to log in on my handheld and try and use that tiny screen and tiny keyboard...

Sorry man

sirgrantalot

well, the amp is in my fc, does that count

how would i go about fixing or replacing the output channel??
or would i not be able to go about it.....

Icemark

open it up and replace the burnt mosfet

sirgrantalot

the mosfets are the black things on the sides of the board right??
im a stereo noob
how would i test to see which mosfet is bad??
i got an old alpine amp that doesnt work, and its got mosfets in it
could i swap them in??
where could i find replacements??

too many questions!!.......sorry

Icemark

The Mosfets are the transistors in the amp, there are two rails of them on each side of the board. I don't know what model you have so its hard for me to say which side the output rail is (although I remember most of the art seires had them on the top edge of the board).

If you can determin which one is blown, then you could in theory replace the burnt one with a new one that had the same numbers (model) on it (if you were able to find a new one somewhere).

Most older alpine amps didn't use a mosfet design transistor. It wasn't until their amps started being designed and built in the US that they started using them.

IMO: I think you are over your head here, and that your mentioned is not sufficent to repair this amp. you would be better off sending it back to PPI and having them repair it for you.

sirgrantalot

in over my head, huh
maybe, but all that hold the mosfets in are the screws that ground them and the solder joints right?
in theory i COULD install new ones right?
if i could find them
in theory

sirgrantalot

my alpiine is a 3533
is that old enough to not have mosfets???

Icemark

yep, the 3533 was a PMR power rail design. (By the way that alpine is a great sounding amp!!!).

Actually most PPI amps used the lower panel of the amp to squeeze the transisters against the heat sink, and were then soldered in.

perhaps you have a really really old amp.

But yes, if you can find the blown fet, figure out what model the fet was, and you could find another (maybe digi-key) you could un-solder the old one and solder a new one in.

sirgrantalot

where would i get that mosfet???

is the model the number on it, i cant remember what the number is now but...


it started doing something wierd just yesterday
some bass will all of a sudden come on, moderate thump, but if i turn the volume all the way down theres a strange thumping sound every second or so
like thump...thump....thump etc

this only happens when theres bass
the bass will cut out sometime completely now.....
is my amp finnally dieing totally??

Icemark

That is from a speaker short... either the wires to the speaker are shorted or the speaker itself has a bad voice coil.

The sound you hear is the amp's outputs switching on and off to protect from a short. After a while the protection cricuit will over heat and the amp will die unless the problem is fixed.

sirgrantalot

where would i get the mosfets???

ive searched some, but what is the best place to buy those chips??

is the mosfet the only thing that i need to change???

Icemark

Digi-Key would probably have them:
http://www.digi-key.com

You need to fix the speaker short first. Also double check that no resisters or diodes got smoked on the board as well (they will look burnt and black if they did).

sirgrantalot

hey thanx man

thanx a ton

ill see if i can fix it

sirgrantalot

hahaha,
damn this thread is going longer than it ever should
with only 2 people posting on it

anyways

ice,
i went to digikey, and for mosfets they have like 4 ro 5 colums that you select certain things for it, like manufacturer and stuff

will the number on the top of the fet be enough to find the right one???

would i just type that number along with mosfet into the search?