LG Flatron Monitor Shows Frequency Exceeded 60Hz After Capacitor Replacement

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#1 21661186 09 Feb 2012 19:21

David Taylor David Taylor

Anonymous

Post #1
21661186 09 Feb 2012 19:21

Hey guys,
I have an LG flatron monitor that the power supply crapped out on. I ended up changing out some capacitors and wah-la I now have power. Unfortunately, I get an error message saying that I have exceeded the frequency output of 60hz. It is now about 67. I didn't have a datasheet for the old caps, but I did honor the values (ex.1000uf/25v). I'm curious as to why the new caps would change the frequency output.

Thanks, David
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#2 21661187 09 Feb 2012 19:58

Steve Lawson Steve Lawson

Anonymous

Post #2
21661187 09 Feb 2012 19:58

I have no idea why this would make a difference in what I assume is the vertical [refresh] frequency, but, it's the only thing I can think of that is filter cap related (assuming the capacitors in question are filter caps (you left a LOT to the imagination ))

A capacitor has more "values" than just capacitance and max voltage. There is also ESR (Effective Series Resistance). For a linear supply this is not a critical value (unless what it is supplying has some sort of high frequency, high current demand. But, for a switching supply (which, again I'm making an assumption, here, based on limited information), the ESR is a very important parameter.

So, one theory is, that you didn't use low ESR cap(s) and thus the power supply is either not supplying the proper voltage(s) at the proper current(s) and that is causing some oscillator in the monitor to not oscillate at the proper frequency.

But, again, that a HUGE shot in the dark!
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#3 21661188 10 Feb 2012 07:33

Ian Fearn Ian Fearn

Anonymous

Post #3
21661188 10 Feb 2012 07:33

Try Changing the refresh rate of your computer. Most flat panel monitors only operate at 60 Hz..
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#4 21661189 10 Feb 2012 10:29

John Albers John Albers

Anonymous

Post #4
21661189 10 Feb 2012 10:29

It is my understanding that most caps that die in applications such as flat screen monitors, die because they have too high an ESR. I recall doing an accelerated lifetime study with a power supply I designed using various ESRs on the filter caps. The ones setups with higher ESR all failed earlier.

If the OP really did replace the caps with higher ESR, wouldn't you expect them to die sooner?
#5 21661190 10 Feb 2012 11:25

Steve Lawson Steve Lawson

Anonymous

Post #5
21661190 10 Feb 2012 11:25

That makes sense. With a higher ESR I would expect the caps would get hotter (in a SMPS), thus the failure mode, right?

But...

"Sooner" than what?

And, what's an "OP"?
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#6 21661191 10 Feb 2012 11:29

John Albers John Albers

Anonymous

Post #6
21661191 10 Feb 2012 11:29

Sooner than the previous caps. That is to say, he might be doing this repair again, in the near future.

OP = original poster? Sorry, I will refrain from internet slang.
#7 21661192 10 Feb 2012 11:38

Steve Lawson Steve Lawson

Anonymous

Post #7
21661192 10 Feb 2012 11:38

No problem, now I know what 'OP' means
#8 21661193 11 Feb 2012 01:44

David Taylor David Taylor

Anonymous

Post #8
21661193 11 Feb 2012 01:44

Thanks for the insight guys. The caps in question are on the output side of the power supply. I have been unable to find datasheets for the originals and ended up replacing with some generic panasonic caps. Based on my limited knowledge and everything I've read, I think Steve has hit the nail on the head. I'm going to try some better caps with a lower ESR and see how it goes. This is more or less a learning experience so discovering the how's and why's makes for a good lesson. I think it would be interesting to compare the outputs with current caps to the outputs of caps with a lower ESR and see what the differences are. The originals lasted about four years with daily use.

Thanks again!
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Topic summary

An LG Flatron monitor experienced a power supply failure, prompting capacitor replacement with generic Panasonic capacitors of matching capacitance and voltage ratings (e.g., 1000µF/25V). Post-repair, the monitor displayed a frequency error indicating the refresh rate exceeded 60Hz, reaching approximately 67Hz. The issue is hypothesized to stem from differences in capacitor characteristics beyond capacitance and voltage, specifically the Effective Series Resistance (ESR). Higher ESR in replacement capacitors, especially in switching power supplies, can affect voltage stability and current delivery, potentially causing oscillators within the monitor to operate at incorrect frequencies. The original capacitors lasted about four years under daily use. It is suggested to replace the capacitors with low ESR types to restore proper frequency output. Adjusting the computer's refresh rate to 60Hz is also recommended, as most flat panel monitors are designed to operate at this frequency.
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LG Flatron Monitor Shows Frequency Exceeded 60Hz After Capacitor Replacement

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