ESR Testing and "in-circuit" -- Please explain - Page 1
Forum section: electronics / beginners

author: crosis
author_rank: Newbie
timestamp: October 30, 2018, 11:59:45 pm
content: I'm looking to repair my Dell E2210f monitor. The monitor turns on fine but the brightness is very dim. I will assume it is a bad capacitor. On visual inspection i see nothing wrong on the power supply board or the other board.From YT videos it seems i will need an ESR Tester not a Capacitor tester; planning on purchasing this onehttps://www.amazon.ca/gp/product/B0779D67SB/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1. What i dont understand is they keep saying i can do the testin-circuit. Does this mean i should perform the capacitor test WHILE the monitor is powered on and active or does this mean to perform the test when there is no power but the capacitor is still within the circuit board?I'm still total sh** at soldering/desoldering so if this magic ESR tester you guys speak of can help me conclusively identify a bad capacitor that will really save me the headache.BTW what can a Capacitor Tester do which the ESR Tester cannot? One person mentioned having both but everytime i read people saying to get the ESR implying the Capacitor tester is pointless. Is the Capacitor Tester poor man's ESR? Why would anyone have both?Thanks

author: sokoloff
author_rank: Super Contributor
timestamp: October 31, 2018, 12:31:56 am
content: Quote from: crosis on October 30, 2018, 11:59:45 pmThe latter for sure!!Quote from: crosis on October 30, 2018, 11:59:45 pmBecause it's another tool/meter/gadget is a good enough reason...ESR testing is more suited to finding "bad caps". You still may want to know the capacitance value of a cap, which an ESR meter will not tell you.

author: crosis
author_rank: Newbie
timestamp: October 31, 2018, 12:52:15 am
content: Thanks, sokoloff. Good response.For the record i just found Dave's ESR video too:

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: October 31, 2018, 02:15:51 am
content: Just to clarify, the instruction would read "perform measurement while circuit is live" or something to that effect, if the device needed to be powered-on during measurement

author: MosherIV
author_rank: Super Contributor
timestamp: October 31, 2018, 07:50:36 am
content: QuoteHi. It is unlikely to be bad capacitors from your desription of what is wrong.It is more likely to be the EL or flourescent back light tubes are going bad.You can get LED replacement kits. Look on ebay.

author: screwbreaker
author_rank: Regular Contributor
timestamp: October 31, 2018, 08:19:16 am
content: Measure the ESR in circuit is complicated.In theory you must know how the caps you are testing are connected, if there are more caps in parallel you never get the correct ESR.But most of the time you don't have any clue of how they are connected, because often you don't have the schematics. And that's also why you end trying with the ESR meter in circuit, because you hope to find something quickly.Generally, if you find an high ESR you got a faulty cap for sure. But with a low ESR you don't know if the cap is good or not, it can still bad, and maybe the ESR meter can't get the correct value in this situation.An ESR meter is a good tool, an is a lot useful sometime. But don't rely too much on them.

author: kripton2035
author_rank: Super Contributor
timestamp: October 31, 2018, 09:09:52 am
content: on my repository (see link in my signature) you can find lots of easy esr meters to build yourself.the one you link is a good one.don't forget an esr meter is not a precision instrument, but it can quickly help you to find bad caps in circuitthere are some configurations (i.e. lots of parallels caps on output power supply) where it can't help without desoldering.*** always shut down the device to test before using the esr meter ***

author: crosis
author_rank: Newbie
timestamp: October 31, 2018, 06:30:18 pm
content: Quote from: kripton2035 on October 31, 2018, 09:09:52 amIm looking to check the larger capacitors (12 in total) on these boards. Do you foresee issues testing these in-circuit with an ESR meter?

author: kripton2035
author_rank: Super Contributor
timestamp: October 31, 2018, 09:32:04 pm
content: they don't seems to be wired in parallel at the output. so yes an "in-circuit" esr meter should help to find quickly a dry capacitor.

author: crosis
author_rank: Newbie
timestamp: November 02, 2018, 04:20:31 am
content: I wanted to give an update on my first venture into testing caps on my low brightness LCD monitor (Dell E2210f).I purchased a MESR-100 ESR Meter (https://www.amazon.ca/gp/product/B0779D67SB). I turned on the unit, attached the alligator clips together, then pressed ZERO. I then proceeded to locate on the leads for the capacitor on the underside of the board. I placed the black and red clips as best i could onto the small nubs that were protruding from the board then tried to keep steady. I cant say the clips were clamping too well but certainly the best i could. I do not have needle tip probes to swap in. All capacitors were tested in-circuit.My results:** Specs represents the IMP value (20'c @ 100khz) pulled from the capacitor maker's spec sheet.1. Su'scon SG 1201 - 470uf 25v (Specs:.038 IMP) = ESR Test Result =.034, .037, .031, .037, .035 << from 5 diff capacitors2. Su'scon SG 1201 - 22uf 16v (Specs:0.8 IMP) = ESR Result = .09, .09, .09 << from 3 diff capacitors3. Su'scon HG 1205 - 100uf 16v (Specs:.210 IMP) =ESR Result = .036, .012<< from 2 diff capacitors4. Jamicon TLP - 680uf 25v (Spec:.070 IMP) =ESR Result: .012 / .025<< from 1 capacitor, fluctuation5. Elite PW - 100uf 450v (Spec:UNKNOWN) ==ESR Result: .369I'm still clueless as to the impedance rating but i assume i want to equal the value or at least be plus or minus 10% within range. Is this correct?For the record i also have a Capacitor Tester which i have not tried as it is my understanding i must first remove the capacitors from the board before testing.I would appreciate any advice on how to proceed with my troubleshooting.Thanks

author: MosherIV
author_rank: Super Contributor
timestamp: November 02, 2018, 07:48:42 am
content: Hi. I already posted saying that from your description, it is not likely to be bad capacitors.Symptons of bad capacitors would be : does not turn on, turns on for a while then turns off by itself.A dim screen is more likely to be the backlight.I looked up your monitor model, it was not clear whether the backlight is EL, flouresnt tube or LED.I would assume it is EL or flouresent tube.As I said before, you can get replacement back light kits.You get replacement EL or flourcent tubes or a kit to replace them with LEDs.

author: crosis
author_rank: Newbie
timestamp: November 03, 2018, 12:50:46 pm
content: Quote from: MosherIV on November 02, 2018, 07:48:42 amThanks, Mosher.This is my first time with such a repair so was hoping the solution would be a simple cheap capacitor replacement. To be honest this is all more an exercise in simple electronic repair than a dire need to restore a monitor. Still though i've explored the capacitor route so will indeed investigate the back light approach.For the record a label on the light back panel reads: LG LM220WE1-TLP4.Search returned - Type: a-Si TFT-LCD , LCM // Light Source CCFL [2 pcs] , 50K hoursAgain, thank you very much, Mosher for helping me out. All this is new to me!

author: MosherIV
author_rank: Super Contributor
timestamp: November 03, 2018, 07:36:48 pm
content: HiNo problem. Hope you learned about capacitors and esr.QuoteThis means "cold cathode flouresent lamp" with a life of 50,000 hours.I think you have reached that limit hence the screen is getting darker because the flourecent lamps are getting dimmer. From your picture of the psu board, they are powered from cn1 and cn2.They should take around 150Volts.The only way to restore the brightness is to replace the lamps.