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How much bulge means a bad cap?

by Integral
Tags: bulge, means
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Integral
#1
Jan29-12, 05:48 PM
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My 50" plasma first lost its component inputs a couple of months ago. I put in a up converting DVD player and more recently went to a Blue Ray on the HDMI inputs and all was good. But now the HDMI inputs have died also.

I pulled the monster off the wall (with some help) and opened it up. I was looking for power supply issues since the component (analog) and HDMI (digital) cannot have much circuitry in common. Also the S-video input with our satellite signal still works fine, so I know it is a issue with the inputs. Thus my assumption of a power supply problem.

Sure enough I found 2 caps with very slightly bulged tops. Both are 3300 μF 100V electrolytic. I have ordered 2 from Allied but am not real confident that this will be a fix.

My question is how much bulge does it take to indicate a bad cap?
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yungman
#2
Jan29-12, 06:07 PM
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If you can see it, it's BAD!!!!

I don't think you can determine like this, first you should measure the voltage first and see what voltage you have on the cap. Then remove one end and see what voltage you have. If you see a jump in voltage without the cap, then you can say the cap is bad.

But at that, you cannot just say the cap is the problem. If the supply gives out over voltage and burn the cap, changing the cap is not going to fix the problem. You have to find out the normal voltage first to determine.
jim hardy
#3
Jan29-12, 06:09 PM
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here's a Wiki link with great photos
http://en.wikipedia.org/wiki/Capacitor_plague
have you a DMM?

the absolute test is how much AC ripple is on them

if you can trace the board and find a spot that's connected to the cap, use the DMM to take both ac and dc readings.
AC value more than a few % of DC value is a likely indicator of open cap.

does that component input board have its own power supply?

I was recently into daughter's 47 inch Vizio expecting power supply issue
(local tv repair ran a forty dollar diagnostic that said it needed a $400 power supply board)
but turned out to be a little microcontoller on main board never telling power supply to start up.
There was a line on power supply called "PSON" which, when driven slightly positive with DMM on Ohms , turned on the supply.
Tracing through the wiring harness she and i found PSON originated on main board, traced that line across board to a postage stamp sized IC with a zillion leads .

New main board fixed it, $150. I can't work on surface mount microcontrollers.


be aware most oriental made DMM's have red lead negative when in ohms position.

good luck!


PS here's a line from that Wiki link

If there are no physical signs, an oscilloscope may be used to examine the AC ripple voltage across capacitors during operation,......excessive ripple or ESR is a sign that the capacitors are faulty.
we poor folks have to use a DMM instead.
in the Vizio all power supply voltages (except primary side of main switcher) were referenced to chassis.

yungman
#4
Jan29-12, 06:39 PM
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How much bulge means a bad cap?

That's the problem in today's electronics, you can't tell head to tail unless you have the schematic. I fixed two of my projection TVs before, they are older and I can still trace the signal and traced back to a burnt horizontal transistor. I had to order the schematic for that. The other was a cold solder joint. But today's stuff are all custom ICs that even if you have the schematic, you don't even know how the signal work.

As an engineer, I always buy extended warranty that cover 5 years. Let's just say, I am ahead!!! I don't even know how many times I brought my VCRs in, printer, laptop and projection TVs. Sometimes they just gave me a new one!!!! It was unlucky that the warranty company went out of business on the projection tv and I was stuck with it the first time, and the second one was out of warranty.....it's 15 years old.
Integral
#5
Jan29-12, 06:42 PM
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Sure I have a DMM and know how to use it. I could have checked voltage out of the PS. But did not. Was not real happy about powering this thing up while it was laying on its face on the floor.

I have fixed another TV and a computer mobo by replacing obviously bad caps. These are not as severely bulged as the others. So am not very confident that this is the problem. Maybe I will get lucky again.

No way I would be able to test these in circuit, there is just no access to the leads. the caps are fairly cheap so I will just shot gun it, if this is not the problem then it is in circuitry that I have no way of troubleshooting or repairing. Just perhaps I can fix a $2500 TV with $12 worth of caps.

I have had experience removing lead free solder with my 25 year old Weller soldering station, so am prepared for what needs to be done.

Some of what I read here gives me a bit more hope.
jim hardy
#6
Jan29-12, 08:14 PM
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Good Luck !

i placed it face down on a quilt
and while had boards out, traced tracks and marked some major test points with a sharpie.

a google on the board number took me to a place in Atlanta (forgot name)
and further research convinced me there's lots of people on Ebay reselling his boards.

still it was a $150 gamble. Well about 125 after returning old one for core refund .



We're pullin for ya!
vk6kro
#7
Jan29-12, 08:14 PM
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I have been looking at ESR meters for testing electrolytic capacitors.

Commercial ones are expensive, but this home-brew one seems interesting:

http://ludens.cl/Electron/esr/esr.html



The transformer may be a problem so I would reduce the frequency and try a small speaker transformer from a transistor radio.

It is possible to mock up a simple ESR meter if you have an audio generator and an oscilloscope.
You put a 1000 ohm and a 10 ohm resistor in series across the output of the audio generator set to 1000 Hz.
The 10 ohm resistor goes at the ground end.

Monitor the voltage across the 10 ohm resistor with the oscilloscope. Try to get a near full scale deflection.

Put the capacitor to be tested across the 10 ohm resistor.
If it is good, the trace on the oscilloscope should almost flat-line. If it is no good, the trace will hardly decrease in amplitude.

It can be used in-circuit if you used fairly thick wire as the test probes. Beware of capacitors that have a charge on them, even after the equipment has been turned off.
jim hardy
#8
Jan29-12, 08:36 PM
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Excellent,,, Vk6, and it's analog !!! ..
i love it.
Integral
#9
Jan29-12, 08:37 PM
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Thanks for that Vk6kro. I just may have to make one of those.
dlgoff
#10
Jan29-12, 11:12 PM
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Quote Quote by Integral View Post
My 50" plasma first lost its component inputs a couple of months ago. ...

Sure enough I found 2 caps with very slightly bulged tops. Both are 3300 μF 100V electrolytic. I have ordered 2 from Allied but am not real confident that this will be a fix.

My question is how much bulge does it take to indicate a bad cap?
Okay, I'm guessing here as to your component input lost.

"Electrolytic capacitor bulging" is not good, even if they test good, so replacing them before they fail is a good idea. But I'm wondering if the problem might be a "software/firmware" problem? I had some weird things (intermittent color palette wrong) happening with my S-video input from my satellite receiver. After resetting the TV "custom settings" for that input back to the default setting and "re-customizing" to my preference, the problem went away.
MATLABdude
#11
Jan29-12, 11:14 PM
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You may want to check with the Badcaps Forums--if it's a problem endemic to your model / series of TVs, you'll find people bitching about it there in the Troubleshooting TVs section (and frequently, you'll find a fix and possibly a full tare-down, too):
http://www.badcaps.net/forum/

A year ago, I replaced all the caps in the power supply of a monitor I had. If it's a filter capacitor (like in the power supply), you'll probably want high-quality, low-ESR ones from reputable manufacturers. If they're Capxon (Crapxon) or any other number of low-quality cap suppliers), you'll probably want to just go ahead and replace the rest of the capacitors while you have the TV open.
Integral
#12
Feb4-12, 12:40 PM
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Thanks all for your input.

It works. Just installed the new caps and we have our HDMI inputs back.

I have not yet built the ESR meter curicut but it is high on my to do lilst.
jim hardy
#13
Feb4-12, 02:40 PM
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I look for Cornell Dubelier or Vishay or Mallory or Sprague - all old line US manufactiurers.

when you get into reserarching elecrtolytics , you find the mix of those electrolytes is trade secrets.

Congratulations on your fix.

I'm thinking VK6's delightful little ESR meter might be expandable to in circuit capacitance measurement as well by applying triangle waves ...


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