CRT Problem - Page 1
Forum section: electronics / repair

author: MMR
author_rank: Newbie
timestamp: September 08, 2014, 05:20:17 pm
content: Friends am facing the problem on CRT single colored, it displays the video in shrinking manner and within few seconds its seems a horizontal line in the middle of crt and after some time crt completely turns off but some noise is there, please guide me on which component i need to take care of

author: N2IXK
author_rank: Frequent Contributor
timestamp: September 08, 2014, 07:23:52 pm
content: By "single colored" do you mean this is a monochrome display, or that only one of the 3 colors on a color display is working?A raster shrinking to a horizontal line indicates a problem in the vertical sweep circuitry. Likely suspects would be electrolytic capacitors or semiconductors in the vertical oscillator or output stages. Another possibility is a failure of a supply voltage that feeds the vertical sweep.Many CRT displays are so-called "hot chassis" designs, and need an isolation transformer for safe troubleshooting. And ALL of them operate on high voltages. Please be careful working on these things...

author: tautech
author_rank: Super Contributor
timestamp: September 08, 2014, 08:08:47 pm
content: Quote from: MMR on September 08, 2014, 05:20:17 pmMMR, you need to give us much more information for pertinent help to be forthcoming.What instrument is the CRT in?What brand and model is it?Do you have a service manual?Do you have the skills and equipment for a repair?Pics?

author: Shock
author_rank: Super Contributor
timestamp: September 08, 2014, 08:55:31 pm
content: CRTs store lethal voltages even when disconnected from the mains. I suggest you don't work on them unless you have experience and suitable equipment.Horizontal deflection shutting downrepairfaq.orgConfirm that the horizontal deflection is shutting down along with the high voltage if it is derived from horizontal deflection: listen for the high pitched deflection whine (NTSC/PAL/CGA), test for static on the screen, see if the CRT filaments are lit, turn up the brightness and/or screen control to see if you can get a raster. Some possibilities:Power is failing to the horizontal output transistor - this could be due to a low voltage power supply problem, bad connection, etc.Base drive to the horizontal output transistor is failing - could be a fault in the horizontal oscillator or bad connection.Problem with the flyback transformer or its secondary loads (flyback may provide other power voltages).X-ray protection is activating - either due to excess HV or due to a fault in the X-ray protection circuitry.If the problem comes and goes erratically it sounds like a bad connection, especially if whacking has an effect. If it comes and goes periodically, then a component could be heating up and failing, then cooling, etc.Horizontal squashedA very narrow picture may indicate problems with the power supply to the horizontal deflection circuits, incorrect scan rate selection or defective components, faulty deflection yoke, or bad connections.If the size is erratic and/or gently whacking the monitor makes the width change, bad connections are likely. See the section: Monitor manufacturing quality and cold solder joints.Confirm that your video card is running at the proper scan rate - particularly that it is not violating the monitor's specifications. An excessive horizontal scan rate is a common cause of a reduced width raster. Try its software setup adjustments as these may have been lost.Beyond this, a schematic will probably be needed to isolate the fault.