Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Chip Amps Amplifiers based on integrated circuits

Can a bad cap kill an LM3875?
Can a bad cap kill an LM3875?
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 2003, 04:48 AM   #1
SRMC is offline SRMC
diyAudio Member
 
Join Date: Sep 2002
Location: Sacramento, California
Default Can a bad cap kill an LM3875?

I built my first Gainclone from Thorsten's inverted LM3875 schematic and one channel works perfectly. However, the first time I powered up the other channel the chip sizzled and fumes came out approx. 3mm above pins 3 and 4 leaving a nice little crater. I have checked to make sure that I have it wired correctly and didn't wire any of the polarized caps backward (been there done that). At this point I can't figure out what went wrong, but I want to learn from this. Could a bad cap on the V- cause this or did I do something wrong?

The cap in question is an old surplus 1000uf 25v cap (all I had left after blowing up my last 50v Panasonic FC) and I don't know how old it is. I have a 260va Plitron w/ dual 18v secondaries and dual bridge rectifier that also powers the other channel so I don't think that the power supply is the problem.

Thanks,
Steve

Hoping to soon have a Gainclone with both channels working
__________________
SRMC
  Reply With Quote
Old 17th April 2003, 01:08 PM   #2
carlosfm is offline carlosfm  Portugal
Banned
 
Join Date: Mar 2003
Location: Lisbon, Portugal
Thumbs down 25v cap?

Hi Steve,

With that transformer you shoud at least use 35v caps.
The cap may blow up because of over-voltage.
Also, are you shure you mounted the cap with the correct polarity?
Remember, on the V- polarity the positive lead of the cap connects to the circuit ground.
  Reply With Quote
Old 17th April 2003, 01:17 PM   #3
JOE DIRT® is offline JOE DIRT®  Canada
diyAudio Member
 
JOE DIRT®'s Avatar
 
Join Date: Apr 2003
Location: Brantford, ON
SRMC.....when anytime you are building an amplifier...first have the outputs of the power supply fused and not connected to the circuit.......apply a light load with a power resistor and then check the voltages.....let it run for awhile....keep a lower fuse value in and connect the amp if all checks out.........another thing is to use a signal injector and make sure the correct path is taken......one little short and you will blow the power amp...hope this Helps!



Cheers!!The DIRT®
  Reply With Quote
Old 17th April 2003, 01:18 PM   #4
Peter Daniel is offline Peter Daniel  Canada
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Can a bad cap kill an LM3875? Send a message via AIM to Peter Daniel
It doesn't seem that cap was damaged, so it's probably OK and correctly connected. Maybe the insulating pad wasn't working correctly and you had negative rail shorted to ground?
__________________
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 17th April 2003, 02:48 PM   #5
SRMC is offline SRMC
diyAudio Member
 
Join Date: Sep 2002
Location: Sacramento, California
Thanks for the help. I have fuses after the rectifier on the power supply output (3a) but I'm sure they are way too high. I used the same mica insulators under both of the chips with a small amount of heat conducting compound that is supposed to be electrically nonconductive (http://www.arcticsilver.com/arctic_alumina.htm). My fear is that although I was using a stepped insulating washer that should have kept the screw centered in the mounting hole and prevented it from touching the chip, the screw attaching everything to the heatsink/case may still have shorted the negative rail to ground.

Thanks again.

Steve
__________________
SRMC
  Reply With Quote
Old 18th April 2003, 02:41 PM   #6
SRMC is offline SRMC
diyAudio Member
 
Join Date: Sep 2002
Location: Sacramento, California
Default Problem solved!

It looks like the prize goes to Peter! It turns out the V- was shorting to ground. I found that I left a tiny burr when I drilled the hole to mount everything on the heatsink, and with the thin mica insulators I was using it still was enough to contact the back of the chip.

Thanks.
__________________
SRMC
  Reply With Quote

Reply


Can a bad cap kill an LM3875?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Will I kill my Tek 2213 guitvinny Equipment & Tools 15 12th March 2014 07:24 AM
Did I kill my B+Ws allquiet Multi-Way 8 29th May 2007 08:16 PM
I want to kill myself with bass.... SkinnyBoy Subwoofers 54 21st March 2005 03:19 AM
Over kill? Scribble Pass Labs 1 21st January 2003 07:27 PM


New To Site? Need Help?

All times are GMT. The time now is 01:29 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki