Repair of Rockford Fosgate Punch 201s - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 11th August 2009, 04:35 PM   #1
diyAudio Member
 
Join Date: Aug 2009
Default Repair of Rockford Fosgate Punch 201s

Hi all.
I use to repair lots of car audio amps, probably 5-10 a month but this one I really cracked my head..
The failure is at LEFT channel and the problem is that the negative side of the output signal is clipping abnormal.
I spent a few hours of logical thinking and some measurements, without finding anything abnormal.
The amp is not loaded at all, I do not connect any of my dummy loads before the amp operates correctly in open load.
Anyways, I've changed ALL small signal SMD transistors, tested with a pair of new output FET's, made resistance measurements to all SMD resistors, everything is correct.
Also, DC levels during idle is the same as the OK channel.
The only difference I can find is, the voltage amplifier stage Q109 and Q111, doesn't give a clean negative swing. It stays a volt or so negative. This compared to the OK channel does drive -13V negative. This is when driving the amp to clipping.
Anyone have any ideas?
  Reply With Quote
Old 11th August 2009, 05:49 PM   #2
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
I'm waiting on a schematic from Rockford.

The problem is possibly an open resistor in the protection circuit. Sometimes it's easy to miss them because they're in parallel with the low value source resistors.

Are all of the source resistors within tolerance?

Did any of the source resistors fail initially?
  Reply With Quote
Old 11th August 2009, 11:46 PM   #3
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Double-check R161, R162 and R163. You may have to desolder one leg of R163 to get an accurate reading on them.

You can disable the protection circuit by lifting D102 and D104. If the amp works properly with those out of the circuit, you know that the audio circuit is OK and the problem is with the protection circuit.
  Reply With Quote
Old 12th August 2009, 03:50 AM   #4
diyAudio Member
 
Join Date: Aug 2009
I found the schematics and uploaded it:
http://www.etanoldax.se/RF201s.pdf

The source resistors is OK. The amp behaves like this even without load, with low output current.
I tried to disable the over current protection circuit, but it didn't do any difference.
Please take a look in the schematics, I'm out of ideas....
  Reply With Quote
Old 12th August 2009, 03:50 AM   #5
diyAudio Member
 
Join Date: Aug 2009
R163 measures like all the others. R162 is not mounted, and R161 is a zero ohm "resistor" and measures zero aswell.
This is the same on the OK channel so probably Rockford made some changes after the schematics were printed.

Like I said in my first post, collector Q111 doesn't go much negative when output calls for maximum swing (when driving into clip). Q111 should be saturated during this condition, and does on the OK channel. It goes only a volt or two negative while the OK channel goes -13V.
This leads to a maximum gate-source (Q115) voltage of 5V, instead of 17V on the OK channel.

I already tried lifting D102 and D104. Helps Nothing!


  Reply With Quote
Old 12th August 2009, 05:02 AM   #6
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
What's the voltage drop across R138, 142 and 146 at idle (no signal)?
  Reply With Quote
Old 12th August 2009, 10:04 AM   #7
diyAudio Member
 
Join Date: Aug 2009
Perry, first of all I like to tell how much I appreciate your time to help me.

Regarding the voltage drops, there is 400mV across R138 and R146, R142 drops only 80mV. In other words there is about 8mA current through the voltage amplifier stage.
These numbers are identical to the OK channel.
  Reply With Quote
Old 12th August 2009, 10:18 AM   #8
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Well, that's about what I have on a similar amp (335mv across the 47 ohm resistors).

Does the emitter of 111 follow the base (minus ~0.6v)? Check it loaded and unloaded. Compare to the other channel.

Does the amplitude of the base drive for 111 compare to the other channel (loaded and unloaded)?
  Reply With Quote
Old 12th August 2009, 04:29 PM   #9
diyAudio Member
 
Join Date: Aug 2009
There is some hokus pokus around Q111. As I tried to explain in a previous post, the collector voltage at Q111 doesn't drive the negative side of output stage very much. I compare both channels when applying a 1.5kHz sinewave, driving both channels a bit above clip so I can see the feedback loop saturating in either direction. It's obvious a big difference to the negative going saturation of Q111, it will just go one or two volts negative compared to positive about +13V. The OK channel goes symmetrical to +13V and -13V during output clipping (feedback loop saturated)

Also, as long as the output is held from clipping there are very small voltage swings at collector Q111. Only when clipping there are high swings (just like a square wave). The failing channel does have a higher voltage swing at collector Q111 at all times, make me believe the loopgain is lower.

It looks like Q111 doesn't get a proper drive level, preventing it from saturation.
  Reply With Quote
Old 12th August 2009, 08:28 PM   #10
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Connect a dummy load to the amp and drive it to moderate clipping. Compare the voltage across the resistors in series with the transistors.

For example, measure the voltage across Rx24 in both channels. If there is more voltage across the one in the defective channel, it means that the amp is working harder to compensate for the error. If there is less voltage drop, determine why there is insufficient current passing through the resistor.

If you see more voltage across R146 than 246, you know that the circuit is trying to pull the voltage negative but something is loading the collector of Q111 (possibly low gain for Q113?).

Work your way through the circuit.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
rockford fosgate punch z stevena2006 Car Audio 2 23rd December 2009 05:20 PM
Rockford Fosgate punch 200aIV audiobahnkid592 Car Audio 2 27th October 2009 02:57 AM
Rockford Fosgate punch/power 500.2 Clipped Car Audio 2 11th July 2007 08:08 AM
Rockford Fosgate Punch sub question audiomachines Subwoofers 4 18th August 2006 02:51 AM
Rockford Fosgate Punch 360a2 dawkins Car Audio 1 6th April 2006 06:27 PM


New To Site? Need Help?

All times are GMT. The time now is 12:47 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2