Tip & How-To about Televison & Video
Your TV lost one of its CRTs and you want to tackle changing it. What to do? You can get a new unit here http://www.encompass.com . The following explanation will help with the replacement.
First we need to cover a few things. CRTs are dangerous and if you have never replaced one before you need to be very careful. If you hit it and cause it to break it will implode which will be very hazardous and life threatening. In addition the CRT contains a charge of high voltage, about 40 kilovolts if not discharged, which could give you a servere shock.
I have found in my 50 years of working on electronics that generally you cannot just replace one crt in a projection tv and get the picture to balance properly. For instance, if the green tube went, how long before the red and blue join it? After all they all have been on the same amount of time. While you may be able to make the picture balance acceptable to you, it will not be perfect. I am a perfectionist, but this is your unit. If you can live with the imperfections I will try to explain the process.
All televisions have a setup procedure and they are all different. You may be able to get a free service manual at http://www.encompass.com as they are putting many on their site now. I would recommend getting the service manual for the setup procedures. If you cannot find it for free you should be able to purchase it at http://www.servicemanuals.net for about $16 US on average. If you plan on doing any future repairs it will certainly pay for itself. If you cannot get one the following generic procedures should help get you through the CRT swap for most units.
First you will have to take out the main board in the bottom of the set. This means disconnecting alot of connectors. Either get wire number tags or use a magic marker to put discreet numbers on every connector so reassembly will be easier. The high voltage section requires the normal respect so as not to get shocked. You should discharge the tube using an insulated wire. Slide the one end of the wire under the high voltage boot on the tube and touch the other end to the chassis. If there is any charge in the tube you will see a large spark. Now the tube is electronically safe, but remember it still contains a vacuum and can implode if damaged.
Disconnect the HV from the CRT. Remove the lense assembly, but make sure you do not change any of the lense settings. You should only have to remove four screws in the corners of the CRT housing.
Remove the CRT board and the yoke. The yoke is removed by unscrewing the screw around the CRT neck and sliding it off. Now remove the CRT by taking out the mounting screws, and being very carefull not to bump it on anything, remove it. Place it in a heavy blanket or a box with bubble wrap in it to cushion it. It should be disposed of properly as it contains heavy metals and dangerous compounds.
Reverse the procedure for reassembly. Once assembled you will have to set the unit up.
Make sure that all the picture controls are in the middle (Picture, Brightness, Color, Tint, and Sharpness). You may or may not have perfect vision but here is a secret to get the focus correct. Turn the control through its range to see where the max focus is, then while looking at a picture adjust the control for the sharpest pixel, not the best focus by your eye, but the sharpest pixels. You will be able to see what I mean when you do it.
Then go to the convergence setup and while displaying a cross hatch pattern adjust the yokes to line the red and blue lines up with the green. Adjust the color drives to match the red and blue with the green.
At this point color balance is important. I have always tried to focus on skin tone since everyone knows what that looks like as well as grass and sky. Anything else can be any color and no one will know if it is correct or not. The color drives are located on the focus divider block which generally is attached to the frame above the flyback and has at least four heavy red wires attached to it. The colors should be marked (R, G, B) and the controls will be above the focus controls for each CRT.
If all went well you should have a working unit with perhaps a good picture or at least acceptable.
Thanks for using FixYa.
Posted by Kim... on
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