Right Channel Problem on LM3875 - diyAudio
Go Back   Home > Forums > Commercial Sector > Vendor Forums > Audio Sector

Audio Sector Kits & PC boards from AudioSector

Reply
 
Thread Tools Search this Thread
Old 27th January 2011, 11:45 PM   #1
freeman is offline freeman  United States
diyAudio Member
 
Join Date: Dec 2010
Default Right Channel Problem on LM3875

Hi All,
Been listening to my LM3875 premium kit for a week, and it was sounding great. But today the right channel faded out suddenly. There is still faint volume there but not much. I've eliminated speakers and source as problem. Voltages on rails and dc offsets are normal. and all continuity tests are checking out. I will need to remove chip from the board to test...correct? Star grounds are set up exactly as Peter suggests. Speakers are 8 ohms and there has been little detectable heat coming from the chips all week. I'm using a PEC 25K pot. Any thoughts are much appreciated. Thanks.
  Reply With Quote
Old 28th January 2011, 01:34 AM   #2
freeman is offline freeman  United States
diyAudio Member
 
Join Date: Dec 2010
Default Additional Info

Forgot to mention that I'm using Avel 330/25+25 transformer. Rail voltages measure about 37V. For heatsink, I'm using 2.5"X1.5"X1/8" alum u-channel in almost same configuration as Peter's build instructions. Any advice is welcome. Thanks.
  Reply With Quote
Old 28th January 2011, 05:08 AM   #3
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Send a message via AIM to Peter Daniel
If the chip shows normal offset (20-70 mV) it's usually not damaged. Check if the offset changes when adjusting volume.

I would suggest swapping complete boards between both channels first and see what happens; removing chips might be tricky.
__________________
www.audiosector.com
“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
  Reply With Quote
Old 28th January 2011, 05:42 AM   #4
freeman is offline freeman  United States
diyAudio Member
 
Join Date: Dec 2010
Default Thanks, Peter

Will do the swap. With full volume I'm getting 24mv on right channel 5.5mv on left. With volume off, 3.7mv on right, 33.1 on left. I'm pretty sure these are similar numbers when I brought it up initially. sound ok?
  Reply With Quote
Old 28th January 2011, 02:28 PM   #5
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Send a message via AIM to Peter Daniel
yes, those look normal.
__________________
www.audiosector.com
“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
  Reply With Quote
Old 1st February 2011, 12:03 AM   #6
freeman is offline freeman  United States
diyAudio Member
 
Join Date: Dec 2010
Peter. I swapped the boards and the right channel still lacked proper volume. I swapped wiring on pins of the pot and low volume shifted to left channel, which means the problem seems to be in front channel of the PEC. Please let me know if you think I've missed something. Is it possible to repair the PEC? Thanks.
  Reply With Quote
Old 1st February 2011, 02:38 AM   #7
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Send a message via AIM to Peter Daniel
If it's the PEC, I assume you changed the wires after the pot?

Here's the link showing how PEC pot is built:"Silver-Carbon" Pot ex Tawan - Photo - & ignore my ugly Pinky!

One way to damage it is by overheating the pins which may disrupt internal connections.
__________________
www.audiosector.com
“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
  Reply With Quote
Old 8th February 2011, 01:12 AM   #8
freeman is offline freeman  United States
diyAudio Member
 
Join Date: Dec 2010
Hey Peter. I swapped the pot out and have it up and sounding great again. Decided not to open up the PEC for now. Now it's on to building a proper chassis if I can pull myself away from listening. Thanks again.
  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
Help with 5-channel LM3875 krips Chip Amps 31 9th January 2009 06:25 AM
3 channel lm3875 help/advice Tristanc1 Chip Amps 8 22nd January 2007 06:04 PM
A 6-channel A/V amp using BrianGT LM3875 boards saabie22 Chip Amps 12 27th September 2005 08:57 AM
5 channel lm3875 layout bjefferys Chip Amps 2 23rd March 2005 10:21 PM
LM3875 Problem nitin Chip Amps 0 23rd September 2004 08:40 AM


New To Site? Need Help?

All times are GMT. The time now is 10:39 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