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Capacitor Rating

Discussion in 'General Electronics Discussion' started by Q2AS, Jan 27, 2021.

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  1. Q2AS

    Q2AS

    6
    2
    Jan 21, 2021
    Apologies for asking something that may seem obvious, but as a mechanical engineer who has spent many years working with industrial control systems, I still get very puzzled by many things electronic.

    I currently have an old, much loved LG monitor that is taking a long time to start up (often requires a power cycle to get it going) and the conventional wisdom is that it's probably capacitors on the power supply that need replacing.

    To practice, I removed the power supply from a similar scrap monitor and have mana ged to download the service manual for that monitor which details the components built into the monitor including the capacitors ....... and this is where my problem arises.

    I am aware that capacitance is measured in Farads, and the common units are milli Farads (mF), micro Farads (uF), nano Farads ( nF) and pico Fards (pF).

    Reading the capacitance value off one of the capitors on the PSU shows it to be 1000 uF 16V, yet reading the manual, the specification for that capacitor shows as 0.1 UF 16V ..... note the upper case U rather than the lower case u (which is actually the greek letter "mu", but doesn't exist on normal keyboards)

    So working on the pronciple that the two are the same, 0.1 UF = 1000 uF, and multiplying both sides by 10, this means the 1 UF = 10,000 uF ??

    It seems really odd that LG have issued a manual using capacitor units that the rest of the world don't seem to recognise ...... or am I missing something glaringly obvious here?

    Thanks
    Capacitor.PNG
     
  2. Martaine2005

    Martaine2005

    3,555
    966
    May 12, 2015
    1 F = 1000000 µF
    1 µF = 1.0E-6 F

    Example: convert 15 F to µF:
    15 F = 15 × 1000000 µF = 15000000 µF

    Farad [F] Microfarad [µF]
    0.01 F 10000 µF
    0.1 F 100000 µF
    1 F 1000000 µF
    2 F 2000000 µF
    3 F 3000000 µF
    5 F 5000000 µF
    10 F 10000000 µF
    20 F 20000000 µF
    50 F 50000000 µF
    100 F 100000000 µF
    1000 F 1000000000 µF
    This was copied n pasted from a website.

    Martin
     
  3. Q2AS

    Q2AS

    6
    2
    Jan 21, 2021
    Thanks, and that is my understanding of a microfarad, no problem, but the issue I have is understanding why a manual would show a value of 0.1UF when the actual capacitor on the board is clearly marked as 1000 µF .....
     
  4. Martaine2005

    Martaine2005

    3,555
    966
    May 12, 2015
    It could quite simply be an error on the schematic.
    I’d go with what values are factory fitted on the board.

    It could also be that somebody repaired it and misread the schematic or didn’t have that value on hand.
    I’ll stick with an error.

    Martin
     
    Last edited: Jan 27, 2021
    HellasTechn likes this.
  5. Q2AS

    Q2AS

    6
    2
    Jan 21, 2021
    Ok, cheers for that , looking longer and harder at the manual makes me think that although it says it's for that monitor, there seem to be a lot of things that are shown wrong when checked against the PSU, so it may even have had a replacement at some stage.

    The forum name is just one that I started using a few years ago. I was trying to find a unique name on another site, and every one I thought of seemed to have gone, so I looked around the office and there was a Mitsubishi PLC CPU sat on the shelf that was called a Q2AS .... and the rest is history as they say.

    Thanks for your help,

    Colin
     
  6. Martaine2005

    Martaine2005

    3,555
    966
    May 12, 2015
    Yes, that too. Many revisions may have been done due to early failures or warranty returns. Only they will know.

    Martin
     
  7. davenn

    davenn Moderator

    13,866
    1,958
    Sep 5, 2009

    Please show a clear photo, just in case there is a misunderstanding
     
  8. bertus

    bertus Moderator

    2,029
    763
    Nov 8, 2019
    Hello,

    Perhaps the manual does not fit the monitor you have.
    What is the type number of the monitor?

    bertus
     
  9. Q2AS

    Q2AS

    6
    2
    Jan 21, 2021
    Thanks to all.

    Last night I stripped the monitor down and had a look at the power supply.

    There were 5 main capacitors on the power supply and 4 of them looked "blown" with domed tops.

    I de-soldered them and tested them using the capacitor checking function on my multi-meter, which I'd never used before, and after realising that you have to give it time to come up with a reading after discharging the capacitor, the readings showed that the 4 "blown ones measured 513 uF and 236 uF (both should have been 1000 uF) and the other two measured 170 uF and 297 uF (both should have been 680 uF). The one without the domed top measured 930 uF (should have been 1000 uF).

    This morning I was able to get replacement capacitors from a local "old school" TV repair man, soldered them in and rebuilt the monitor and lo and behold, success ...... monitor is now fine.

    Not very often I get a good result when I do these things, so I was well chuffed.

    I think it confirms that not everything you find on the internet is exactly what it claims to be as the service manual shows capacitor values completely different to the ones I found on the board, and even fails to mention one that obviously existed, hence my initial confusion.
     
    davenn and Martaine2005 like this.
  10. Martaine2005

    Martaine2005

    3,555
    966
    May 12, 2015
    Well done.
    Scratch that on your bed post and search for something else to repair.
    Job satisfaction guaranteed.

    Martin
     
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