Rockford 301s Won't power up

Rockguy

Member
2016-06-25 4:27 am
I pulled the amp apart and the culprit was obvious. Q6 is burnt up badly. The top bubbled so bad I can't read a part number to get a replacement. I cleaned all of the carbon up with alcohol and it doesn't appear anything else overheated.
Does anyone know what part number Q6 is? Thanks in advance.
 

Perry Babin

Member
Paid Member
2003-11-20 11:01 am
Louisiana
www.bcae1.com
I don't have the 301 but you can get it from Rockford if no one here has it.

Q6 is the same as Q7. Likely an IRF3205.

The gate resistors, Q7, the driver transistors are all suspect. It's possible that the output transistors failed causing the power supply to fail.
 

Attachments

  • rockford - punch401s-4331.pdf
    495.3 KB · Views: 62
  • rockford - punch201S-4307 Schematic.pdf
    418.4 KB · Views: 81

Rockguy

Member
2016-06-25 4:27 am
I don't have the 301 but you can get it from Rockford if no one here has it.

Q6 is the same as Q7. Likely an IRF3205.

The gate resistors, Q7, the driver transistors are all suspect. It's possible that the output transistors failed causing the power supply to fail.

Thank you for that Perry. I emailed Rockford to ask about that. I haven't heard anything back to this point. Q7 is indeed a IRF3205. A close inspection of it reveals a little hole on top of it so, if it hasn't already failed, it's probably going to. What a joy getting those off is going to be.
 
They are easy to get off if you have a small butane torch. Cut the legs on the transistor, heat gently while gently pushing the transistor to the side. When the solder melts, it will slide off.

You'll need to tine the backs of the replacements before soldering them down. This is best done with a soldering iron at about 600°F.

The hole is made from the inside of the transistor as it fails.
 
I think it should but I've never used that model.

If it can't quite get it hot enough, the combination of the torch on bottom and a soldering iron on the tab of the transistor will be enough.

When you do this shield the board with a couple of layers of aluminum foil. With the legs cut from the transistors, you can wrap the foil around the edge of the board.
 

Rockguy

Member
2016-06-25 4:27 am
I've never used one. I just googled when you suggested it. I removed a transistor like that once from a tv board. I used an iron. It was in a tight spot. It tore up part of the board underneath but, the new one went in and worked fine. It took awhile to get that thing hot though.
I saw on youtube today, a guy used a griddle to heat the bottom. Another guy said take a frying pan and turn it upside down and use a low flame. The Rockford looks like that little board comes out by itself.
 

Perry Babin

Member
Paid Member
2003-11-20 11:01 am
Louisiana
www.bcae1.com
You can use whatever heat source that you have. I've used an 1157 lamp to aid the soldering iron in heating. Whatever you use, stop heating precisely when the transistors slides and protect the board.

I've used the little weller that was on that page but it's 2x as expensive. The weller was marginal for boards with more, closely spaced parts. I now use a chef's torch but one like I use would be too expensive for one job.
 

Rockguy

Member
2016-06-25 4:27 am
Thanks for that pointer. Will do.

I was reading through your tutorial on amp repair. Great job on that. Very informative. I followed it and took some measurements. Q6 and Q7 are obviously bad so I know I will be ordering those. R20 by Q7 is visibly damaged and has audible continuity. It has a 330 on it and from reading here I believe it's a 33 ohm gate resistor. The other gate resistors seem to be measuring accurately but, if they are cheap, I may just order some in case. I took all measurements in circuit. I read where that might throw it off. I may cut the legs of the suspect pieces and remeasure.

For now I tried your form on the IRF540s. They are quite different. I'll start with that and see what you think.
 

Attachments

  • IRF 540 readings.jpg
    IRF 540 readings.jpg
    100.8 KB · Views: 74

Rockguy

Member
2016-06-25 4:27 am
I'm looking around on mouser and I'm a little baffled by the numbers on the resistors. I filtered them by 33 ohms because the resistor on Q6 has a 330 on it and measures 33 ohms. I figure the one on Q7 (which is R20) is the same. On mouser though, I'm seeing a 1001? That doesn't seem to make sense with what I was reading on your tutorials.
 

Rockguy

Member
2016-06-25 4:27 am
Thanks Perry. I see that's digikey. Not a problem, I can do them. I'm looking at the IRF3205 and from google searching, it says lower RDS on resistance will make it run cooler. However lower RDS has a lower current drain. 75A compared to 110A. Am I digging too deep? I was googling to see what the important characteristics are.