Green Convergence problem
O.K. This is a CRT Projection TV see
The Manual is available from
http://www.tacp.toshiba.com/tacpassets-images/models/50H82/docs/50H82_om_e.pdf , and this describes the Manual Convergence process, I doubt this will help, but it's step #1.
The problem you are describing sound to me like a deflection problem. The electron beam in the green projection 'tube' (a super bright CRT) is probably not being controlled correctly.
This can be caused by several things, from least likely to most :) I do not recommend that someone untrained in electronics attempt to service a CRT based television due to the potential for extreme shock or electrocution.
That caveat said, here are the possibilities.
#1 Physical Trauma: The TV has been shifted moved or bumped hard, and one or more of the fixed permanent magnets used to help convergence has come loose, or the CRT projection tube was damaged.
I don't think these TVs use convergence magnets anymore, but it's possible.
The green CRT tube failing would be more likely if all four corners were affected, but I've seen a failing CRT affect a single corner/edge before.
I believe that this model has projection tubes that are separate from the colored filters, so swapping the tubes around may be possible. I do not have a service manual for this set, and this may be a hazardous operation due to high voltages.
#2 Stray magnetic field: Someone dropped a magnet into the TV, and it landed close enough to the green tube to effect it only, or perhaps some other piece of equipment is effecting JUST the Green CRT (clock radio, speaker, badly designed wall wart, etc.). Removing the offending magnetic field may cure the problem.
Perhaps the offending magnetic field has been removed, but it's presence is still felt. Try using the degauss function built into the TV set (I can't find one in the manual, but it may be present). You may want to try using a degaussing coil, and see if that helps the problem. Just be careful not to get the coil too close to the base of the projector tubes.
#3 Deflection drive electronics: A CRT works by using an electron beam to excite fluorescent compounds on the face of the CRT. To move the electron beam about, a process called deflection is employed. Magnetic coils (the choke) are used to steer the electron beam up, down, left or right. These coils are driven by transistors, and as one fails, you will get an image that starts collapsing in the affected section.
On a standard CRT TV, that would mean the entire image is affected, but a CRT projection display uses separate red, green, and blue CRT projection tubes to build the image, so you have three times the deflection, three times the possible transistor failures, and in your case, the odd result of just the green part of the image displaying incorrectly.
This problem will probably require a service call, and a electronic board swap, but the problem could be the choke (the magnetic coils) on the green CRT projection tube.
Swapping the green tube for another tube could prove if it's the tube or if the deflection electronics that are going out.
Again, my feeling is that this is a deflection issue requiring a board swap (I doubt anyone actually does component level repair anymore)
Sorry, I don't have a better answer,
Jan 13, 2007 |
Toshiba 50H82 50" Rear Projection...