All About Circuits Forum  

Go Back   All About Circuits Forum > Electronics Forums > General Electronics Chat

Notices

General Electronics Chat Discussion forum for general chat about anything electronics related, including asking questions about material in the All About Circuits E-book, Worksheets, and Videos.

Reply   Post New Thread
 
Thread Tools Display Modes
  #1  
Old 02-14-2009, 07:30 AM
jecarts jecarts is offline
Junior Member
 
Join Date: Feb 2009
Posts: 12
Default help in repairing crt monitors

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.....!!!!!!!!!
Reply With Quote
  #2  
Old 02-14-2009, 07:43 AM
bertus's Avatar
bertus bertus is offline
Super Moderator
 
Join Date: Apr 2008
Location: Amsterdam,Holland (GMT + 1)
Posts: 11,584
Default

Hello,

What type of monitors are there ?
Here is a site with some tips for different monitors.
http://www.e-repair.co.uk/tipsmon.htm
http://www.repairfaq.org/sam/monfaq.htm

Greetings,
Bertus
__________________
You don't have to know everything, if you know where to find it.
When you do ask questions, you may look stupid.
When you do NOT ask questions, you will STAY stupid.

It would be nice to have the Timezone ( GMT +/- x ) in the location field in the profile.
(User CP -> Edit Your Details)
Reply With Quote
  #3  
Old 02-14-2009, 07:51 AM
jecarts jecarts is offline
Junior Member
 
Join Date: Feb 2009
Posts: 12
Default

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
Reply With Quote
  #4  
Old 02-14-2009, 08:01 AM
bertus's Avatar
bertus bertus is offline
Super Moderator
 
Join Date: Apr 2008
Location: Amsterdam,Holland (GMT + 1)
Posts: 11,584
Default

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
__________________
You don't have to know everything, if you know where to find it.
When you do ask questions, you may look stupid.
When you do NOT ask questions, you will STAY stupid.

It would be nice to have the Timezone ( GMT +/- x ) in the location field in the profile.
(User CP -> Edit Your Details)
Reply With Quote
  #5  
Old 02-14-2009, 01:54 PM
beenthere's Avatar
beenthere beenthere is offline
Senior Member
 
Join Date: Apr 2004
Location: Missouri, USA (GMT -6)
Posts: 15,815
Blog Entries: 10
Default

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.
__________________
First comes the hardware, then the software.
Reply With Quote
  #6  
Old 02-16-2009, 03:03 AM
jecarts jecarts is offline
Junior Member
 
Join Date: Feb 2009
Posts: 12
Default

Quote:
Originally Posted by beenthere View Post
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.

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?
Reply With Quote
  #7  
Old 02-16-2009, 03:07 AM
jecarts jecarts is offline
Junior Member
 
Join Date: Feb 2009
Posts: 12
Default

Quote:
Originally Posted by bertus View Post
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

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......
Reply With Quote
  #8  
Old 02-16-2009, 05:45 AM
bertus's Avatar
bertus bertus is offline
Super Moderator
 
Join Date: Apr 2008
Location: Amsterdam,Holland (GMT + 1)
Posts: 11,584
Default

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
__________________
You don't have to know everything, if you know where to find it.
When you do ask questions, you may look stupid.
When you do NOT ask questions, you will STAY stupid.

It would be nice to have the Timezone ( GMT +/- x ) in the location field in the profile.
(User CP -> Edit Your Details)

Last edited by bertus; 02-16-2009 at 06:27 AM.
Reply With Quote
  #9  
Old 03-02-2009, 01:51 AM
jecarts jecarts is offline
Junior Member
 
Join Date: Feb 2009
Posts: 12
Default

thanks for the help..................
__________________
Smile always!
Reply With Quote
Reply   Post New Thread

Tags
, ,


Related Site Pages
Section Title
Worksheet High-reliability circuits
Video Lecture Troubleshooting Strategies - Circuit Troubleshooting
Video Lecture Troubleshooting Series Circuits - Circuit Troubleshooting


Similar Threads
Thread Thread Starter Forum Replies Last Post
Repairing Switched Mode Power Supplies (SMPS) GS3 General Electronics Chat 8 08-08-2012 01:54 PM
Repairing a Infinity 7541a 4 Channel Amp Sirenguy General Electronics Chat 7 06-17-2008 03:16 PM

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 11:23 PM.


User-posted content, unless source quoted, is licensed under a Creative Commons Public Domain License.
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.