help in repairing crt monitors

Discussion in 'General Electronics Chat' started by jecarts, Feb 14, 2009.

  1. jecarts

    jecarts Thread Starter Member

    Joined:
    Feb 8, 2009
    Messages:
    12
    I am a technical support in one of the big hospital in our place. As of now we have lot of defective monitors. We are only two in IT department and i have only small knowledge of it because i am a newly grad. Some of the monitors are i think have a slight defect, and can be repaired but i don't know what are the hint or techniques what specific part or components will be replaced. Can anyone help me with this, can give me some diagrams or ebooks or anything else that can help me solve this problem??? Any reply will be appreciated... thanks.....!!!!!!!!!:):):)
  2. bertus

    bertus Administrator Staff Member

    Joined:
    Apr 5, 2008
    Messages:
    12,620
    Location:
    Amsterdam,Holland (GMT + 1)
  3. jecarts

    jecarts Thread Starter Member

    Joined:
    Feb 8, 2009
    Messages:
    12
    Hello,

    They are all CRT Monitors, some of them doesn't turn on, some the display will disappear when accidentally touch


    Thanks a lot for the reply
  4. bertus

    bertus Administrator Staff Member

    Joined:
    Apr 5, 2008
    Messages:
    12,620
    Location:
    Amsterdam,Holland (GMT + 1)
    Hello,

    When the display fails afther touching, there will be a lose contact somewhere.
    Take a close look at the PCB and look for soldering placed that have gone dul with a lose wire in it.
    When you found such spot solder it agian.

    Greetings,
    Bertus
  5. beenthere

    beenthere Retired Moderator

    Joined:
    Apr 20, 2004
    Messages:
    15,815
    Location:
    Missouri, USA (GMT -6)
    Please be aware that the CRT can hold a possibly lethal charge for hours after power is removed. That voltage must be discharged safely. One uses a thin screwdriver with a long shaft.

    Clip a lead to the shaft near the handle and the other end of the lead to ground (circuit ground inside the monitor). Carefully slide the end of the screwdriver under the high voltage lead rubber cap and angle it downwards to contact the metal lead or the aquadag. After the initial pop, leave the screwdriver in place of several minutes to complete the discharge.

    If your monitors are all the same, you may be able to make comparisons from a good one to one with a problem. What test equipment do you have? Just as important, what experience in electronic repair do you have?

    No insult, but LCD displays are the only way to go. They may be less expensive to buy than what it takes to fix a CRT monitor.
  6. jecarts

    jecarts Thread Starter Member

    Joined:
    Feb 8, 2009
    Messages:
    12

    Our monitors are all CRT's but they are of different brands, we have multi tester and about the electronic experience i have i little experience and i cant trace a component that is defective... can u give me some tips on how to use the multi tester to trace what component has defect?
  7. jecarts

    jecarts Thread Starter Member

    Joined:
    Feb 8, 2009
    Messages:
    12

    Hello...

    when the problem is blur display of monitor what possible component may have defect? and if the display has become smaller and it does not fit in the monitor?

    thank you so much for any reply......
  8. bertus

    bertus Administrator Staff Member

    Joined:
    Apr 5, 2008
    Messages:
    12,620
    Location:
    Amsterdam,Holland (GMT + 1)
    Hello,

    When the trace is blur there is something wrong in the focus part.

    From the page I already gave you :

    Excessive high voltage

    Any significant increase in HV should cause the X-ray protection circuits to kick in and either shut down the set or modify the deflection in such a way as to render it harmless. Symptoms include arcing/sparking of HV, smaller than normal picture, and under certain scenarios, possible excessive brightness.
    Causes of the HV being too high are:


    1. Excess B+ voltage to the HOT. The likely cause is to a low voltage regulator failure.
    2. Open snubber capacitors across the HOT. These are under a lot of stress and are located near hot components so failure is possible.
    3. Incorrect excessively long scan drive to HOT caused by failure of horizontal oscillator/sync circuits. However, other things like the HOT will probably blow up first. The picture will definitely be messed up. This is more likely with auto-scan monitors than TVs since what is too long for one scan range may be correct for another and the selection circuitry is confused or broken.
    4. Failure of HV regulator. Actual HV regulators are uncommon today but the HV may controlled by a feedback voltage from a divider (focus or screen, or its own) or a secondary winding on the flyback setting the B+ or drive timing. This may result in an underscanned (smaller than normal) picture if only the HV and not the deflection voltages as well are derived from the same supply.
    In one example of (4), a arcing of the HV in a Conrac studio monitor resulted in the destruction of the HV switchmode inverter transistor (this used a separate HV supply) and a fusable resistor. The cause was an open HV feedback resistor divider allowing the HV to increase drastically.

    Greetings,
    Bertus
    Last edited: Feb 16, 2009
  9. jecarts

    jecarts Thread Starter Member

    Joined:
    Feb 8, 2009
    Messages:
    12
    thanks for the help..................
Similar Threads
Forum Title Date
General Electronics Chat Repairing vintage hi fi Aug 17, 2014
General Electronics Chat Repairing/replaceing a small motor Nov 25, 2013
General Electronics Chat Repairing cheap chinese charger Oct 13, 2013
General Electronics Chat Repairing MISSING solder PADS Aug 21, 2013
General Electronics Chat air conditioner Repairing May 31, 2013

Share This Page