Rockford Fosgate Punch 200x2 Old School Repair

[Mike Stephenson]

Hello,
I have a Rockford Fosgate Punch 200x2 that went up in smoke. Apparently some water leaked inside the trunk and into the amp. Before I knew water leaked in, I started the car and the amp powered up. Immediately after powering up, the amp produced a fairly loud output to the sub at around 60-70 Hertz. It did that for about 5 seconds and then it stopped and lots of smoke came out.

I then took the amp apart and accessed the damage. It looks like the power supply FET's fried. I cleaned up a lot of black soot, using a Q-Tip and Alcohol. There was a lot of soot over a lot of components because the amp was mounted vertically and the power supply FET's were at the bottom.

I replaced all 4 FET's with IRF3205s and replaced the 4 gate resistors with 47 ohm resistors. I've included links to the parts below. I then wired power and ground to the amp without the remote signal. I put a 10A fuse inline with B+. When I connected B+, there was a small arc on the wire I connected to the B+ terminal, but nothing crazy. After 10 seconds or so, I put 12V on the Remote connector. The 10A fuse blew as soon as Remote was connected, so I know something else is bad.

I visually inspected the components, and don't see any other obvious signs of damage.

Here's an image of the damage. In this image, I had just started cleaning up the soot, but then stopped to take a picture before I cleaned it all up. The amp was mounted vertically, exactly like the image shows. I believe there's a lot of soot above the power supply FETs because the soot went vertically. I suspect, but not positive, that a majority of the components above the PS FETS are good. Let me know if I should check them

I'm looking for a recommendation of what components to check now. I'd appreciate any help. Thanks


Links to parts used so far:
IRF3205PBF International Rectifier | IRF3205PBF-ND | DigiKey
CRCW080547R0JNEA Vishay Dale | 541-47ACT-ND | DigiKey


Mike

 

[Perry Babin]

Apply only remote and ground (no B+) and post the DC voltage on all gate legs (as close to the body of the transistor as possible) of the power supply FETs.

 

[Mike Stephenson]

Thanks for the fast reply. Here are the numbers:

Q7 - 4.58v
Q11 - 4.58v
Q6 - 4.66v
Q10 - 4.66v

Mike

 

[Perry Babin]

Do you have a scope?

Have you checked the output transistors to confirm that none are shorted?

 

[Mike Stephenson]

I have a friend that has an oscilloscope that he's going to loan me. I'm going to pick it up later this morning. I'm not sure exactly which components are the output transistors. Are those the other devices that look like the PS FETS and are pressed against the heatsink?

Mike

 

[Mike Stephenson]

Also, when checking for shorted output transistors, am I looking to see if each leg is shorted to ground, or to each other leg, or both?

Thanks,
Mike

 

[Mike Stephenson]

I now have an oscilloscope in hand.

 

[Perry Babin]

First, post 1 photo of the waveforms for the FETs on each side of the amp with the scope probe on the gate leg of the FET, closest to the body of the FET. If the adjacent FETs have identical waveforms, you only need to post a photo for one FET on each side.

Read the 'best initial settings' on page 73 of the car audio site (link in sig line below).

 

[Mike Stephenson]

OK. It looks like I took a step backwards for some unknown reason. I went to get the measurements with the scope and I now don't get any voltage on the gates of any of the PS FETs. The PS FETs do have 12v on the center leg and close to ground on the leg opposite the gate. I assume a lot of other stuff depends on the PS FETs working correctly. Let me know if there's something I can check now. Thanks for the help so far.

Mike

Mike

 

[Perry Babin]

Do you have 12v on pins 8, 11 and 12 of the 494?

 

[Mike Stephenson]

No, there isn't any voltage on those pins.

 

[Perry Babin]

Follow the remote voltage from the remote terminal through D1 to pin 12. Where is the voltage lost?

 

[Mike Stephenson]

I think one of my problems that was throwing me off earlier was the fact that my battery was low at around 10v from the car not being driven much. I started the car so the alternator runs and took some measurements. With a 10A fuse between the battery and B+ the fuse doesn't blow without the remote terminal. As soon as I apply 12v (actually 14.9 because the alternator was running) to the the remote terminal, the fuse then blows. So it looks like the remote circuit is working to some degree. I took some voltage measurements on the legs of the FETs and only see voltage (14.9v) on the middle pin (drain) of the 4 PS FETs. All of the other FETs don't show any voltage.

Mike

 

[Perry Babin]

A low battery won't prevent voltage from being driven to pins 8, 11 and 12.

Let the battery charge and re-check the drive signals on the gate legs of the FETs with no B+.

 

[Mike Stephenson]

OK. Battery is at 12.1v now.

Q7 - 4.71v
Q11 - 4.71v
Q6 - 4.79v
Q10 - 4.79v

 

[Perry Babin]

Did you confirm (with the oscilloscope) that all are identical?

 

[Mike Stephenson]

Sorry for not mentioning that. They all look identical. Here's what they look like. The probe was accidentally set to x10

 

[Mike Stephenson]

Here it is with the Probe x1. They all look the same

 

[Perry Babin]

Do you have a way to limit current?

Are all of the bias controls set to the fully counter-clockwise position?

 

[Mike Stephenson]

I don't have anything in particular to limit current, but I can build a circuit or something to do so. Let me know if there's a particular device to use or a circuit I can build. I do have some resistors, diodes etc laying around and I'm close to a Frys Electronics to purchase something. I also have a breadboard to use. I haven't messed with the bias controls yet, so I'm not sure where they're positioned. I can rotate them to full counter-clockwise position when I get home this afternoon.

Thanks again for taking the time to help me on this. I appreciate it.

Mike