Can i use general purpose capacitor in a power supply on a monitor - Page 1
Forum section: electronics / beginners

author: muffenme
author_rank: Contributor
timestamp: August 09, 2015, 06:27:39 pm
content: I have a Benq G2220HD that the back light started to flicker. I assume failing capacitor, so I looked at digikey.ca website and found the capacitor made by Panasonic but they are general purpose capacitor. Could I replace the capacitor from my power supply, oh my original capacitor doesn't look like they need replacement even though I don't have a way to test them.

author: mariush
author_rank: Super Contributor
timestamp: August 09, 2015, 07:13:24 pm
content: You need to use Low ESR capacitors.Digikey will say "general purpose" to a huge selection of capacitors so you can't use that to pick.Look for Panasonic FM , FR , United Chemi Con KZE, KZH, KY, KYA , Nichicon HW, HM, HN (the last two if still available) etc etc

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 09, 2015, 11:24:33 pm
content: In a pinch, absolutely.For long life? Probably not. What are its ratings? Look for high temperature, long life, low impedance and so on.Tim

author: muffenme
author_rank: Contributor
timestamp: August 11, 2015, 03:57:18 pm
content: none of the capacitor show sign that it has failed, for ex bulging on top. Could a failing transformer show the same sign because the coils appears to be not as shinny and the board around the transformer is darker, but could be normal.

author: AKM
author_rank: Contributor
timestamp: August 11, 2015, 04:42:11 pm
content: If the capacitor on the inverter was bad, the monitor would usualy either not power on at all or would work without backlight and it would come on after the capacitor heated up. Try heating up the capacitor with a hairdrier for a few short intervals(don`t heat it for too long, it may explode) power it up; if it starts without flickering, replace it.But, flickering backlight is probably due to old ccfl tubes which you can only replace. If you can dissasemble the panel, you will probbably notice the blackening on the tube ends; same as in standard flurescent tubes and CFL-s.To the original question, you could replace the capacitor with a general purpose capacitor, but it would fail within few months or weeks. You would have to use a much higher capacity one.

author: muffenme
author_rank: Contributor
timestamp: August 11, 2015, 05:00:57 pm
content: The backlight is supposed to be LED'S not CCFL.

author: muffenme
author_rank: Contributor
timestamp: August 11, 2015, 05:20:38 pm
content: The monitor powers up no problem but the back light slowly gets bright. Ever so often it flicker.This is the photo of the power board.

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 11, 2015, 06:06:22 pm
content: De-solder the old capacitor and test it with a multimeter which tests capacitance. connect it to a voltage equal to it's rated voltage and measure leakage current. If it is good don't mess with it, put it back.Those caps are simple garden variety caps in a garden variety power supply. You could re-use other caps from salvaged equipment if you like to. Always use caps that have an equal or higher voltage written on them and the same value written on them. You can add two to make one if you look up how to add caps together.

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 11, 2015, 06:09:03 pm
content: Quote from: muffenme on August 11, 2015, 05:00:57 pmLeds only use low voltage, and are not as popular in monitors as fluorescent panels which use high voltage but give off light evenly across the entire panel, and are cheap.

author: muffenme
author_rank: Contributor
timestamp: August 11, 2015, 06:57:06 pm
content: thank for all the information I received.

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 11, 2015, 07:00:42 pm
content: You're welcome. (and bring more questions 8-) I likes!)

author: mariush
author_rank: Super Contributor
timestamp: August 11, 2015, 09:19:59 pm
content: The backlight is CCFL, not leds. It's obvious when you see that big high voltage transformer near the four connectors for CCFL tubes.There's two pairs of bulbs, in each pair the tubes are in series and the transformer basically powers them with about 1500v and a few mA.A common failure mode is for the wire at the end of one of the tubes to make a bad connection, basically the wire unsolders from the end of the tube and then it makes contact or not depending on your luck... simple fix would be to resolder the wire.Other times the wire starts arc-ing with the metal of the lcd screen and that can be also fixed by resoldering and insulating that lead better.Anyway, both of these diagnostics involve opening the lcd screen which is really not that easy, if you're amateur there's a big risk you'll crack the lcd panel. You have to be really careful to put everything back in the same order (there's thin lcd panel and layers of special plastic foils and plastic panels that are designed to spread the light evenly across all lcd screen).. it's a hassle.