rockford p300-1 heating up

[gmoney123]

hey i have a rockford fosgate p300-1 and it blew on me so i changed the mosfetts for ones that were compatible (similar) since the correct ones were out if stock. The tech at digikey said their shouldnt be any trouble with the replacements, but now the amp seems to heat up steadily until its blazing hot... any help?

 

[Pano]

Is this a Class-D amp?

 

[gmoney123]

ya its a class D amp, its a 2 channel 300rms class D sub amp. Originally i had it installed by a local shop, a day later when i turned my car off after driving the amp stopped working. I took it off, opened it, the mosfetts had blown (substantially more on the main pin), so i ordered more that seemed compatible and installed them. Same problem the moment i turn off my ignition the amp blew. I decided to put a relay with a diode on the return infront of my amp and it now works without blowing up, however there is a constant heat increase until the amp feels like its going to burn up... help plz!

 

[81bas]

from description here Rockford Fosgate® - P300-1 I found it is a MONO 300w amp. With single inductor/transformer inside

I suppose it is a usual class AB amp, and you need to setup the bias (quiescent current) using this blue trimpot...

 

[gmoney123]

ok cool, any chance i can get a step by step guide? im an electronics newbie but i know basic stuff

 

[81bas]

Hi,

it would be better to find it from the service manual, I think
Or ask it here: Car Audio - diyAudio

 

[Pano]

I also think it is class-ab, but the docs don't say. I think I'll move this to the car audio section were it will be better seen.

 

[Perry Babin]

If you set the bias pot to the fully counter-clockwise position, does it still heat up (no signal, no speakers)?

 

[gmoney123]

just at work for another few hours but i will try and set the pot to fully counter-clockwise (off im guessing) when i get home and report back

 

[brandes.cm]

Future show stock on both the FQA28n15 and FQA36P15, these are used in the outputs of that style of amp. The power supply uses HUF75344.

 

[gmoney123]

ya sorry i havent gotten time to check yet, but your saying to remove the amp and hook it upto a DC power supply with no load attached? I have a DC supply but its low amperage...

 

[Perry Babin]

Yes, no signal, no load.

What's the current rating of the supply?

Does it have an amp meter on it?

 

[gmoney123]

my supply has .5 amps at 120v, it has no ammeter though lol, im guessing im gonna have to buy a 10:1 transfo to step down to 12v tho...

 

[Perry Babin]

There's no need to buy a transformer. Power it up in the vehicle.