oldschool rockford fosgate repair

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
When the amp was installed was there any DC voltage on the RCA shield ground?

Have you checked the resistors that are in line and near by to see if any were out of tolerance after you replaced the part?

I will look at the schematic and see what its purpose is.
That's the power mosfet, you will have to replace all the IRFZ44's and their gate resistor (it should be around 33-100ohms).

The diode that blew up first is tied to your power control circuit (power supply/ 494 IC & 339) just by looking from the top of the circuit board and following its traces.

Have you checked the outputs and predriver's? They maybe shorted and hence why your power supply took a dump. Did you have a fuse in B+ when testing, if so what rating/amperage?
I would use IRF3205 and change the gate resistors to 47 ohm and replace the power supply drivers with MMBTA56 and MMBTA06.

I would replace the power supply caps and rail caps. I would also change any aluminum cap on the board.

This is for long term reliability. Although some of the caps may not be bad why wait until they are, the damage they do is sometimes un-repairable.
The power supply failed.

Do you want this to happen again?

Do you want the amp to be reliable?

You Must:

Replace ALL the power supply FETS
Replace ALL the gate resistors for the power supply FETS
Replace ALL the power supply drivers marked 1A and 2A by the TL494 chip

Providing nothing is wrong in the output section you should be good to go.

Be sure to turn the bias pots fully counter clock wise, all the way down.

When powering the amp after your repair use a current limiter and a small fuse like 10 amp.

The bias can be reset after the repair is completed.
"Also how do i change it to 47 ohms"

The gate resistors are the small little black chip looking pieces hooked to the gate leg of each power supply FET and or the first leg. The first leg is the one all the way left if your looking at the FET straight on.

These need to be changed regardless wether you use the original FETS or the 3205's.

You need to change the drivers for the power supply as well. Look for the big TL494 chip and there are 4 transistors near it marked 1A and 2A, these must be changed. They are small and black and have 3 legs each.
Check the gate resistors and you need to replace all of the power supply mosfets. Not just the blown ones. They all have to be the exactly the same.
If you just replace the one it will play for a little while and go right back out.
I would not buy them from amazon or ebay there are a lot of counterfeits of that particular part. Get them from a reputable distributor. Try MCM electronics
My friend If you are not experenced with a soldering iron and have some experence with SMDs(surface mount devices)You need to practice on something else before attempting the repair.
And the answer is no you do not need to replace every output transister. Just the ones in the power supply .
Once you get the power supply up and going you can see if both the right and left channell are playing fine and not drawing excessive current.
Listen to what Seancane told you to do in the post that starts with.
The power supply failed.
If you think the repair my be too much for you to handle. I have all the parts in stock to compleate the repair.
Mail it to me I will finish the power supply for $60.00 if a channell is out $35.00 for each.Set the bias as part of repairing the power supply.
If you are not a very expierenced solder man . You may want to consider this.You can mess the board up in just a few seconds and the amp will never play again.
A few questions you may want to ask yourself before attempting the repair.

Do you have a good volt ohm meter that has a scale of Rx1 on it? You will need this while finding the gate resistors.

Dose the volt Ohm meter have the capability of measuring DC Amps on the scale of
500MA or higher? You will need this when setting the bias of right and left channels

Do you know where the BIAS pots are located and have you turned them all the way down.

Do you know how to hook the VOM in series with the amp so you can set the bias?

Have you successfully removed and replaced SMDs? This is the question I am worried about. Practice on something else other than the Rockford Fosgate. Make sure you have successfully removed and replaced a resistor and a transistor or two before attempting work inside the amp. The outputs and the diode were easy these are not. Practice on something else besides the amp. One little mistake can ruin the board.

Do you know which end of the amp is the power supply and which is the two channels? The end with the RCAs is the end with the two channels.

If you are serious about doing amplifier repair work look up Perry Babbins Amplifier repair page. You can find a link in his post on this web site in the car audio section.
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.