Beginner Question - Do these capacitors look suspicious? - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

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 8th December 2008, 07:59 PM   #1
diyAudio Member
 
Join Date: Dec 2008
Default Beginner Question - Do these capacitors look suspicious?

This is my first post and I'm a total noob so I apologize for being clueless.
I have collected a couple receivers with the hope of maybe repairing them. Through reading on this forum and others, I think one of them is suffering from bad capacitors. I have Yamaha HTR-5540 (pretty low end) receiver that my buddy had in his basement for at least two years. It emits a mean sounding buzz from all sources (CD, tuner, aux, etc) through both speaker and headphone outputs. The buzzing changes in tone a bit as you fiddle with the settings (ie, itís a little different on mute than not on mute) but in general the buzz is constant and loud regardless of volume level.
Iíve read that grounding can cause issues but I donít think thatís my problem. The circuit it's on is quite properly grounded and there's nothing plugged into the receiver save the AC, a speaker, and a single source. It buzzed at my friendís house, too, so I really donít think itís a ground issue.
First off, does this behavior sound like a capacitor problem? What else could it be?
Iíve attached a pic of the most suspicious looking caps. This forum seems to require tiny pictures and only one at a time (hey it's free) so I hope you can see what i mean about these. The two on the lower left look perfectly flat on top and others look ever so slightly bulgy. If the pictures show clearly bad caps then at least I know for sure where to start.
Attached Images
File Type: jpg dscn0584 ultra low resolution.jpg (92.8 KB, 347 views)
  Reply With Quote
Old 8th December 2008, 08:23 PM   #2
diyAudio Member
 
Join Date: Dec 2008
Default here's another cap

The two biggies say "AUDIO 8200uF(M) 63V 85 deg C" on them and again, I can't tell if they are obviously bad or not. Both look this one. The bulging could just be due to the stamping on top - it's hard for me to know.
Attached Images
File Type: jpg dscn0586 ultra low res.jpg (61.9 KB, 287 views)
  Reply With Quote
Old 8th December 2008, 11:02 PM   #3
diyAudio Member
 
Join Date: Aug 2008
Check all of the grounding connections. Circuit board and everything. I don't think it is the capacitors but its always a possibility. Those capacitors are called bipolar and bipolar capacitors are always stamped like that (of course there are different ratings and sizes but you get the idea). If you have extra ones laying around of the same exact ratings then replace them and see what happens. I think it could also be a transistor problem but I'm not 100% sure. It could also be the output of the audio's main connection meaning where the audio is output before the switches such as after going through part of the circuit. It all runs off the same audio current. If you had schematics or something maybe it would help others.
  Reply With Quote
Old 9th December 2008, 11:27 AM   #4
diyAudio Member
 
Join Date: Dec 2008
Quote:
Originally posted by M50SNIPER
Check all of the grounding connections. Circuit board and everything. I don't think it is the capacitors but its always a possibility. Those capacitors are called bipolar and bipolar capacitors are always stamped like that (of course there are different ratings and sizes but you get the idea). If you have extra ones laying around of the same exact ratings then replace them and see what happens. I think it could also be a transistor problem but I'm not 100% sure. It could also be the output of the audio's main connection meaning where the audio is output before the switches such as after going through part of the circuit. It all runs off the same audio current. If you had schematics or something maybe it would help others.

Thanks!
How could the grounding of the circuit boards have gotten messed up? from sitting in the basement? Isn't a grounding connection just a metal connection to the metal frame, which is in turn connected to the ground wire in the power line? I don't understand how something could spontaneously become ungrounded without my having poked it with a screwdriver or dropped it or something. Would I be checking for a loose wire or what?
  Reply With Quote
Old 9th December 2008, 01:45 PM   #5
diyAudio Member
 
Sonusthree's Avatar
 
Join Date: Dec 2005
Location: Sussex, UK
Ground connections are not only found between the circuit board and case. They are also within the PCB itself.

Lots of things can affect electrical connections over time ...

Remember that different materials expand and contract at different rates for the same change in temperature. This causes stresses .... and this becomes even worse when the solder joint is 'dry' ( as in 'dry joints'.
Dampness and corrosion of contacts is also a factor.

__________________
Martin
+ + =
  Reply With Quote
Old 9th December 2008, 05:49 PM   #6
diyAudio Member
 
Join Date: Dec 2008
Default VICTORY!

Thanks for the suggestion! I thought I'd have to learn how to replace capacitors, but the solution was just a plain old grounding connection.

I looked at each circuit board and each one had a copper screw in it attached either to the metal base of the receiver or there was a fairly substantial wire coming from the circuit board leading to a copper screw in some other board which was in turn attached to the metal frame.

All the connections were clearly tight except for one. I attached a pic of the offending connection. As you can see, there's a black wire attached to the board with the copper screw. The wire leads to a board up toward the front of the receiver that is not otherwise grounded.
That little wire was loose, causing the metal in its connector to touch the wire protruding up from the circuit board marked TP381.

I positioned the black grounding wire such that the connector didn't touch anything metal except the grounding screw and then I tightened it down firmly. On powering the receiver back up, the buzz was completely gone and the unit sounds great - at least, way better than it sounded yesterday!

I am very pleased to have fixed this problem so easily and quickly but I'm not thrilled with the engineering of this product. Doesn't it seem bound to fail? The copper screw is an inch long and it passes through two layers of steel - one immediately below the circuit board and then another half an inch further down. Given that the linear expansion rate of copper is significantly higher than that of steel (the material of the receiver's frame) it seems like the designers should have realized that plain old thermal expansion and contraction could eventually loosen the screw a bit.
So instead of using a loose fitting connector, they should have used something that affixes to the grounding screw or to the circuit board more firmly. It's especially annoying because of the obvious big metal prong sitting there right beside the grounding wire - it's just waiting for that little connector to loosen and make contact and viola - the receiver is broken for want of twenty minutes consideration on the part of an engineer at Yamaha.
  Reply With Quote
Old 9th December 2008, 05:50 PM   #7
Speakerholic
diyAudio Moderator
 
Cal Weldon's Avatar
 
Join Date: Jan 2004
Location: Near Vancouver
No picture
__________________
Next stop: Margaritaville
Some of Cal's stuff | Cal Weldon Consulting
  Reply With Quote
Old 9th December 2008, 08:55 PM   #8
diyAudio Member
 
Join Date: Dec 2008
Default Re: here's another cap

The bulging is due to them creating gasses internally. They are failing or at least starting to fail!


Quote:
Originally posted by ceomrman
The two biggies say "AUDIO 8200uF(M) 63V 85 deg C" on them and again, I can't tell if they are obviously bad or not. Both look this one. The bulging could just be due to the stamping on top - it's hard for me to know.
I don't know if it's worth replacing them or not, it depends on your motivation. They might continue to "work" for a while, but they are definitely failing.

You could pull them out and test them on a cap / esr meter and be sure but anytime the top of a capacitor is bulging, it has vented (internally at least) and is bad / going bad.

When they are new, all the "stamped" tops of capacitors are totally flat. The creases you see in various forms allow the visual display of failure and to allow for the cap to fail with a slower / hopefully more controlled fashion. Kind of like crumple zones on a car control how the car will "fold" during an accident. These weak areas in the top allow for a predictable pattern of expansion from within.

Imagine lighting a firecraker when it's intact. Boom. Take another and break it in half, giving the expanding gasses somewhere to go, and it just fizzles a bit.

When the capacitors are wrapped too tightly and have the expanding gasses they are more likely to pop/explode. It's also easier to tell visually when they are beginning to fail by the bulges you see on the top.

This is all too common in computers from 2002-2004. Take a look at http://www.badcaps.net for more pictures and explanations.
  Reply With Quote
Old 11th December 2008, 09:58 PM   #9
diyAudio Member
 
Join Date: Dec 2008
Default here's a pic of what I did to fix it

Quote:
Originally posted by Cal Weldon
No picture
Here's the pic of the offending connection, btw. When I found it, the silver connector at the end of the black wire was a bit loose, causing it to rotate clockwise and touch the pin jutting up from the board marked TP381.

The capacitors may or may not be in the process of failing, but I guess we're all going to die someday. They sound great today, at least!


Click the image to open in full size.
  Reply With Quote
Old 11th December 2008, 09:59 PM   #10
Speakerholic
diyAudio Moderator
 
Cal Weldon's Avatar
 
Join Date: Jan 2004
Location: Near Vancouver
Thanks,

Since you've been so good, I've released you from moderation.
__________________
Next stop: Margaritaville
Some of Cal's stuff | Cal Weldon Consulting
  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
Beginner question/s OB tjthe1st Multi-Way 2 20th December 2007 05:09 AM
Just being suspicious on a russian webstore ... Lord Winter Parts 2 17th June 2006 10:52 AM
Suspicious NE5532 wxn Parts 22 13th February 2004 08:48 PM
Power supply decoupling capacitors (beginner question) bm_mode Solid State 5 26th March 2002 01:29 AM


New To Site? Need Help?

All times are GMT. The time now is 03:09 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