old school rockford punch 40dsm messes up fm reception horribly. - 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 17th April 2011, 11:36 PM   #1
diyAudio Member
 
Join Date: Apr 2011
Location: parts unknown
Default old school rockford punch 40dsm messes up fm reception horribly.

hello diyaudio, i was wondering what would cause an old-school rockford punch 40dsm (1992-93 vintage) amplifier to mess up fm reception horribly. i got this amp from a friend who had something wrong with it, where it wouldnt power on because of a blown diode. the good news is that replacing the diode made it work (and BOOOOY does it sound oooh so good), but i have a big problem with the reception. what happens is that when i turn up the volume, static interference from the amplifier gets worse, even on my strong local stations, and does it regardless of what head unit i have it hooked up to. i REALLY want to use this amp but i cant put up with my amplifier wreaking havoc with my radio reception. if this will help, i have included a pic that shows the diode i replaced. the 1n4003 diode (the one labeled "cr7" on the board closest to the power terminals with the burn marks) by the metallic green electrolytic cap is the one that was burnt and i replaced. any info would be great.

thanks
  Reply With Quote
Old 18th April 2011, 12:32 AM   #2
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
CR7 is supposed to be a 1N5366, not a 1n400x. This 'may' make a difference since the 5366 is used to clamp spikes on the power supply. It's likely that you have other power supply issues. You would need an oscilloscope to determine if the waveforms are OK or excessively noisy.

It's also possible that you have a problem with your antenna cable. It should be shielded which should prevent the amp from causing problems with reception.
  Reply With Quote
Old 18th April 2011, 01:07 AM   #3
diyAudio Member
 
Join Date: Apr 2011
Location: parts unknown
thanks a bunch, sir/madam. i didnt know that it needed that kind of diode; it was burnt so bad that i could barely make out the reading. about the antenna cable: i have my pioneer deh-p4900ib stereo installed in a honda crx where i have a very cheap made plexiglass vr3 wally world amp installed in the center console right under the headunit (its a bitch finding good mounting locations for amplifiers in those small cars where i dont have to do any modifications) and i have absolutely no problems with noise. this rockford is an awesome amp and i love how they underrate the watts of this gem; THEY MAKE AMPS LIKE SH** TODAY!! the quality of these amps is the reason why i want to fix it.
  Reply With Quote
Old 18th April 2011, 01:08 AM   #4
diyAudio Member
 
Join Date: Apr 2011
Location: parts unknown
you also mentioned oscilloscope. i havent had any experience using one; how would i go about hooking one up to the amp?
  Reply With Quote
Old 18th April 2011, 06:01 AM   #5
diyAudio Member
 
Join Date: Apr 2011
Location: Anchorage AK
Have you tried an amp of similar power level, or checked your grounds yet? Engine compartment as well. Another thing is if it has a toridal or not one of the reasons they switched to torroids is that they don't emit the electrical noise as a traditional... It may be old enough to be non-torroid, in which case you would need to place the amp further away from any antennae run....
  Reply With Quote
Old 18th April 2011, 06:53 AM   #6
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
I've never seen those diodes blow unless the amp was connected with reverse polarity (which almost always destroys the FETs also) or if the amp had a problem with the power supply.

You use the scope much like you would a voltmeter but the scope can show you things that a multimeter cannot.

If you remove the cover and measure the voltage on the first leg of the power supply FETs, you should read ~5v on each of them. If one is significantly different than the other, that would indicate that there is a problem. Do NOT slip when measuring the voltage and insert a 10 amp fuse in the B+ line feeding the amp to 'help' protect it if you do slip. Place the black meter probe on the amplifier's ground terminal. Place the red meter probe on the point where you need to measure the voltage.
  Reply With Quote
Old 18th April 2011, 12:32 PM   #7
diyAudio Member
 
Join Date: Apr 2011
Location: parts unknown
Quote:
Originally Posted by AKHeathen View Post
Have you tried an amp of similar power level, or checked your grounds yet? Engine compartment as well. Another thing is if it has a toridal or not one of the reasons they switched to torroids is that they don't emit the electrical noise as a traditional... It may be old enough to be non-torroid, in which case you would need to place the amp further away from any antennae run....
the vr3 amplifier i have also uses a torioid as well as the rockford, but the vr3 outputs no noise at all even under the console (as mentioned, its a doosy to find other spots to mount an amp in that small car). the ground is good (wire less than a foot; i put the dremel with a sanding wheel on it to clean off the paint for a good connection).
  Reply With Quote
Old 18th April 2011, 12:47 PM   #8
diyAudio Member
 
Join Date: Apr 2011
Location: parts unknown
Quote:
Originally Posted by Perry Babin View Post
I've never seen those diodes blow unless the amp was connected with reverse polarity (which almost always destroys the FETs also) or if the amp had a problem with the power supply.

You use the scope much like you would a voltmeter but the scope can show you things that a multimeter cannot.

If you remove the cover and measure the voltage on the first leg of the power supply FETs, you should read ~5v on each of them. If one is significantly different than the other, that would indicate that there is a problem. Do NOT slip when measuring the voltage and insert a 10 amp fuse in the B+ line feeding the amp to 'help' protect it if you do slip. Place the black meter probe on the amplifier's ground terminal. Place the red meter probe on the point where you need to measure the voltage.
gotcha. i priced an oscilloscope and it was pretty high and i dont have that kind of money to invest in something i will only use occasionally (i have a digital voltmeter, though). does a bad power supply also run excessively hot; i ask because when i bench tested the amp on an old computer power supply. it barely got warm, even though i cranked the hell out of it with 2 ohms into both channels and bridged to a 4 ohm sub (tri mode). the amp sounded awesome and played stably (and still ran cool) when i hooked it to my ipod or when playing a cd but not the fm, and interference was less on the am, what a surprise (YES i listen to good ol' am too).
  Reply With Quote
Old 18th April 2011, 01:18 PM   #9
diyAudio Member
 
Join Date: Apr 2011
Location: parts unknown
which ones are the power supply transistors, the ones to the left or to the right if i was looking at the amp with the power terminals facing me?
  Reply With Quote
Old 18th April 2011, 01:37 PM   #10
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Q1 and Q2.
  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
Alpine FM reception sigfrid Car Audio 26 18th April 2011 02:07 PM
AM Reception for Sherwood S-7900A AM/FM Receiver leomags Solid State 1 18th August 2010 02:56 PM
Punch 40DSM no output on either channel brandes.cm Car Audio 33 27th June 2010 04:52 AM
Mp3 player FM reception. v-bro Parts 0 4th December 2006 12:06 AM
How to improve FM reception? bm_mode Analogue Source 23 18th August 2004 11:18 PM


New To Site? Need Help?

All times are GMT. The time now is 11:23 PM.


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