Beginner Question - Do these capacitors look suspicious?

[ceomrman]

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, it’s a little different on mute than not on mute) but in general the buzz is constant and loud regardless of volume level.
I’ve read that grounding can cause issues but I don’t think that’s 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 friend’s house, too, so I really don’t think it’s a ground issue.
First off, does this behavior sound like a capacitor problem? What else could it be?
I’ve 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.

[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.

[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.

[ceomrman]

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?

[Sonusthree]

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.

[ceomrman]

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.

[Cal Weldon]

No picture

[chipinnc]

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

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.

[ceomrman]

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!

[Cal Weldon]

Thanks,

Since you've been so good, I've released you from moderation.