Rockford fosgate punch 201s 600w repair

Westwind

Member
2020-01-06 11:22 pm
Hi every one,
I'm new to this forum and this is my first thread.
I've blown my amp myself because of my short knowledge abt amps electronics. First there was a problem with the speakers connected to the amp, they were whining along with the car rpm. I tried every tip on the net I came across, but in vain until I foolishly decided to open the amp and move one of the two resistance regulator switches ( I hope I named them right) while the amp was on. As a result some smoke started to raise from the motherboard and the positive lead with the negative lead started to get really hot.
Any ideas abt what i've done to my amp and where to start looking. I really want to fix it myself if possible. I learned that mosfets are the electrical components which fails most in amps.
I tried to upload a picture of the motherboard, but it didn't. I'm not sure why. I'll try later.
Thanks in advance
 
The file size may be the issue with the images. I'll post the instructions for posting at the end of this post.

You likely turned the bias pots, indicated by yellow arrow in attached photo.

Is that what your amp looks like internally?



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Westwind

Member
2020-01-06 11:22 pm
If you turn those pots fully counter-clockwise, does the amp still work?

Do this with a 5-7.5 amp fuse inline and with the MEHSA strips clamped to the heatsink.
The amp is not working. I think something was blown when I turned the pots clockwise. I measured resistance between the pot legs and found out that turning them clockwise increase resistance, counter-clockwise decrease resistance. What's the function of the pots? I need to know what went wrong when I turned them.
 
The pots are similar to the idle speed setting on a car. If it's set too low, the engine won't run right or may even stall. Set properly, the engine will sit and idle perfectly. Set too high and the engine will waste energy, run hot, etc.

When you set the pots too high, you essentially set the idle at full throttle and it blew. Here is a demo that shows the setting procedure.
http://www.bcae1.com/temp/ausettingbias.swf

You need to read the following page from top to bottom.
bcae1.com - Car Amplifier Repair Tutorial - The Basics

You likely blew the output transistors, possibly burned the resistors that overheated and possibly burned the power supply FETs.
 

Westwind

Member
2020-01-06 11:22 pm
I took the resistors out of the board and measured them, no resistance at all. Multimeter indicates 8 ohms, but my multimeter indicates 8 ohms just by touching the leads together. One more thing is that when I tried to calculate the resistance from the colour codes i've got 300m ohm with 5% tolerance. the resistors got black orange gray gold. Is my reading correct. Am I on the right path or I'm missing sth?
 

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Westwind

Member
2020-01-06 11:22 pm
Hello friends,
back again. So, as described at the beginning of this thread, messing up with the bias pot which is being referred to as rv104 on the board (variable resistor, value at max is 2k ohms) blew two MOSFETs, sfp9540 and irf540.
Now that I need to replace those two MOSFETs, I'm afraid they get blown too because of the bias pot whose ideal adjustment was changed.
So, my big concern now is how to readjust the bias into its ideal position before refitting the new MOSFETs.
 

Westwind

Member
2020-01-06 11:22 pm
The current draw shown by the amp meter is what's important. The position of the potentiometer is irrelevant. You just want to see a slight increase in current for each channel.

In the schematics, the value of the bias is 2k ohms, which is the maximum value when the bias reaches the end towards clockwise. Can I depend on resistance to set the right safe value? If yes, what value of resistance the bias should sit at?