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draganm
Joined: 08 Mar 2006
Posts: 8990
Location: Colorado
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| Posted: Tue Jun 22, 2010 3:10 pm Post subject: |
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| deronmoped wrote: | | I really think there must be several things going on to cause caps to fail. What makes me think this is, I have other electronic devices that never see a cap failure, even after decades. We know heat accelerates the demise of them, but what else are candidates that cause them to fail sooner.Thanks, Deron. |
ripple currents cause premature failure although I belive they are usually associated with boards delivering significant amounts of power like a deflection circuit? I wouldn't expect to see a ripple current on a purely RGB driver board?
the only exception would be if the RGB board is sharing a power rail with another board generating ripple. This is where a strong EE background coems in handy as determining what's going on here requires some serious time staring at schematic's.
Barring that, simply swapping out the ones close the heat-sink is a good starting point. The way the heat sink is situated suggests is would trap a lot of heat under it?
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deronmoped
Joined: 03 Nov 2006
Posts: 1154
Location: San Diego
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| Posted: Tue Jun 22, 2010 5:02 pm Post subject: |
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| Sparky015 wrote: | Deron,
Sounds like you may have a bum ESR meter, or it's out of calibration. If a cap is leaky, it will most certainly read out of spec on an ESR meter. Also, are you comparing your readings to the cap datasheet? There are all different kinds of caps, some designed for low ESR, some not. It's important you have a hard spec you are testing to, to understand if the cap is outside it's normal characteristics. |
I have a Dick Smith ESR meter. I have checked known good caps to see how they would read compared to the ones I was testing installed in circuit boards. The meter seems fine and there is a listing of good ESR values right on the face of the meter.
From what I have read, most caps can be all over the place in their tolerances and still work fine. That is why you can use quite a bit higher rated uf caps in a circuit and they will be fine. If you have a shorted cap, now that is a big problem, a open cap might give you problems.
Deron.
Last edited by deronmoped on Tue Jun 22, 2010 5:13 pm; edited 1 time in total
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deronmoped
Joined: 03 Nov 2006
Posts: 1154
Location: San Diego
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| Posted: Tue Jun 22, 2010 5:11 pm Post subject: |
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| draganm wrote: | | deronmoped wrote: | | I really think there must be several things going on to cause caps to fail. What makes me think this is, I have other electronic devices that never see a cap failure, even after decades. We know heat accelerates the demise of them, but what else are candidates that cause them to fail sooner.Thanks, Deron. |
ripple currents cause premature failure although I belive they are usually associated with boards delivering significant amounts of power like a deflection circuit? I wouldn't expect to see a ripple current on a purely RGB driver board?
the only exception would be if the RGB board is sharing a power rail with another board generating ripple. This is where a strong EE background coems in handy as determining what's going on here requires some serious time staring at schematic's.
Barring that, simply swapping out the ones close the heat-sink is a good starting point. The way the heat sink is situated suggests is would trap a lot of heat under it? |
That is what is strange, you would think my video out board would not have that much stress on it as my deflection board. Yet I'm still on the original deflection board and this is the fifth video out board I'm on.
I cleaned the board and I'm going to test it to see if the crap that leaked onto the board was causing the problems. I'm curious to see if cap pee would effect a circuit.
Yeah I'm going to target the caps located close to the heat sink first, there are at least two in that area that are leaking onto the board. I do not want to get into changing out a hundred of them. My other problem is, I pretty good a soldering, but why take the chance of causing problems from doing unnecessary work.
Deron.
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draganm
Joined: 08 Mar 2006
Posts: 8990
Location: Colorado
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| Posted: Tue Jun 22, 2010 6:36 pm Post subject: |
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| deronmoped wrote: | Yeah I'm going to target the caps located close to the heat sink first, there are at least two in that area that are leaking onto the board. I do not want to get into changing out a hundred of them. My other problem is, I pretty good a soldering, but why take the chance of causing problems from doing unnecessary work.
Deron. |
It's hard to say what's necessary with any piece of electronics that's 10years or older but target the known leaky ones and see what happens.
I have a feeling this board does more than just video out. the large power transistors on top suggest maybe some higher voltages are being generated like G2? If so that's a roughly 400 Volt output.
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