Best way to identify defective capacitors

Discussion in 'General Electronics Chat' started by maxxxxel, Aug 21, 2006.

  1. maxxxxel

    Thread Starter New Member

    Aug 21, 2006
    1
    0
    Hi,

    I recently got a Dell 2000FP LCD monitor. It still works fine but it has a known component temperature-related problem - if the monitor had been switched on for say 30 mins it cannot be switch off or on again, when removing the power (20v power supply) and plugging it in again it would get stuck in its boot-sequence or lock in standby mode. It works again after cooling down for an hours or so. I have read on some of the monitor repair forums that this standby problem is known problem caused by some of the SMD capacitors going high in ESR .

    I have a few questions to fixing the problem

    - how well do Capacitance Meters work?

    - Would this meter do the job or can anyone recommend a good ESR meter?
    http://www.kompotek.no/goxpage00000112dbp00003.html
    http://cgi.ebay.com/NEW-In-Circuit-...ryZ73173QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

    - All of the caps are Aluminium Electrolytic - Surface Mount but some are harder to identify without a schematic, does anyone know of a good site to identify capacitors


    Thanks
    David
     
  2. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,276
    1,067
    The ESR meter is the quickest way to go. I bought one from Dick Smith's site about 8 years ago. There are various models out there and do a search for ESR meters and I'm sure you will find one to your liking and price.

    The scale you see on that first link's meter might not be for the type of capacitor that your testing. Sometimes it's best to compare a new one with the one in your monitor until you have your own "knowledge base" of the typical readings for that particular type of capacitor.

    http://www.google.com/search?hl=en&q=+"esr+meter" is the google search for ESR Meters
     
  3. Chris Wright

    Well-Known Member

    Jul 26, 2006
    62
    0
    I was surfing and I ran across this claim: "I recently found an easy and cheap way to test ESR (Equivalent Series Resistance) of electrolytic capacitors, in circuit, that might save some people a lot of time. It requires only an oscilloscope and a simple signal generator" at the following site:

    http://www.fullnet.com/u/tomg/esrscope.htm

    Got a scope or a friend with one?

    Or Better yet, Build your own? It looks pretty simple and cheap:

    http://ludens.cl/Electron/esr/esr.html
     
  4. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    4
    I can vouch for the method linked by Chris above. Quick and easy to do.
     
  5. Joe S.

    Member

    Aug 28, 2006
    10
    0
    It sounds as if you are chasing a thermal problem, either an intermittant due to a cold solder joint or a component which opens or shorts out at operating temp.

    I would invest in a can of that cold shot spray and get your significant other's hair dryer as a heat source and go for a little hunt, these kinds of problems occur I believe largely due to the extremely low wages electronics firms pay and their failure to invest in proper training and quality control. That is why the third world is fast becoming Manufacturers Mecca.

    I SEE YOU ARE WORKING ON AN LCD MONITOR - FOR ANYONE WORKING ON A CRT MONITOR THE FOLLOWING APPLIES:

    A WORD OF CAUTION : STAY___ AWAY___ FROM___ THE__ CRT___ HIGH___ VOLTAGE__ AND__ FLYBACK__ CIRCUITS, THEY ARE DEADLY, I OPENED UP A 17" MONITOR TO TROUBLESHOOT IT AND WHEN I POWERED IT UP A SPARK TRAVELED 8 INCHES ACROSS THE OUTSIDE OF THE CRT TO GROUND.
    THATS 200 MM TO EVERYONE NOT IN USA. The CRT will store this High Voltage for Days, maybe even weeks.
    I do not frighten easily, but the size and intensity of that spark, canceled any plans I had of repairing that monitor, I put it back together and put in the dumpster.
    Regards
    JS
     
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