CRT Computer monitors

Discussion in 'General Electronics Chat' started by RodneyB, Feb 28, 2013.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    Before everyone falls off their chairs I know that it is not viable for repairs to be done on CRT monitors with the introduction of all the new monitors which are very reasonably priced.
    Often when international companies and first world companies upgrade their computers the existing ones are in perfect condition. These machines are then very kindly often sent to Zimbabwe where Rotary to whom I am a member of assemble them into working units and distribute them to rural schools so that children who may never use a computer until they are expected to at work get the opportunity to learn computer skills.
    The biggest problem we face is the monitors are often faulty or not working properly shimmering or just not coming on. I would like to get some basic guide lines to go about fixing these.
    I have contacted the manufactures who all have a pretty standard reply that this range has been discontinued and therefore no documentation.
    So my question is, Is there anyone who can guide me through the basic things to check and how and if possible where I may find an archive of old circuit diagrams so that I can at least try to fix them before they get thrown away.

    Many thanks

    Rodney
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    absf likes this.
  3. MrChips

    Moderator

    Oct 2, 2009
    12,421
    3,355
    It helps to work on the same brand and model in batches. This way you become familiar with the unit. Also having a working unit can help trouble shooting the broken ones.

    First step is to check the power fuse and any other internal fuses.
    Next, check power cables, power switch for discontinuity.
    Check the VGA connector. I have seen bent pins that prevent proper signals.

    From here on it gets more tricky.

    The usual failure modes are bad horizontal driver power transistor.
    Bad power supply capacitors.
     
  4. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    if you let me know make and model ive most probably got the service manual as i still am asked to repair this type of monitor which on the whole are much better built than the rubbish lcds available now and last far longer and once you know the basics are very easy to repair to component level
     
  5. absf

    Senior Member

    Dec 29, 2010
    1,492
    371
    Recently repairing my CRT monitors, I discovered a lot of dry joints on bigger ICs, high wattage resistors, transistors and chips on heat sinks.

    Some of them are hard to spot unless you use a magnifying glass that was used for repairing watches. High voltage caps >160V especially those near to the EHT transformer are more likely to get faulty.

    Some of the newer monitors came with a MCU that controls the screen functions. And if this chip has lost its program or become faulty. It would also be tough to source a new one.

    Like what Mr Chips said, grouping the same models together and repairing one model type in batches is the easiest approach. Usually the same model monitors would have similar problems as from my past repairing experience. Power supply stage is also one of the places where most of the problems are started.

    Best of luck on your trouble shooting:)

    Allen
     
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