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Originally Posted by SPL db
Greetings!
Sorry if this post is in the wrong forum, but I wanted to ask this pretty quick...
We have a classified section on our work intranet home page called the Trading Post.
The new issue comes out on Thursdays which would be today...
Long story short, there is an ad for a 52" Mitsubishi rear projection TV for $50!
I'm going to go look at it tonight, the guy says that it works great, but he's noticed that the picture
is getting dimmer... he states that the picture is still good, just not as bright as it used to be.
My question is what could be the problem that would cause a rear projection to start going dim?
I know that with a CRT, going dim usually means the tube is going bad...
Does this mean with a rear projection the guns are going bad?
Thanks!
Scott
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If this is more than say, 7 years old or so, I would be VERY hesatint to buy it!!
But you will no doubt ask me "but I know people with projo's that are 10,15 even 20 years old, that still look as good as new, so this one should be ok right??
And my answer is-- I AGREE that a LOT of older projos can and often DO look very good, and they can last a long time-- 20+ years and still have near-perfect tubes. I own a 1994 model RCA projo, with hitachi tubes, and it looks BETTER than a lOT of newer sets!! this is NOT an exception to the rule, neither. Those old Hitachi-type sets(with tubes made by them) will last and last.. Maybe the splitter or fly might fail, or something a lot more minor, and in the Hitachi's, the STK's will no doubt need replaced, but the tubes will go on and on, unless someone watches them about 24/7. I would be willing to estimate that the sets with hitachi type tubes could get 35-50k hours on those tubes, (if they are good from the start), before the tubes become too weak to use. In the biz, those tubes are known as 'bulletproof"!!
Now, before you get thoroughly confused and say I am contradicting my own words, let me go on a bit. I said the projos with HITACHI tubes are good!! BUT... mitsibushi projos have VERY weak tubes that have TWO types of problems, that tend to start within FIVE years old and often SOONER!!
The FIRST problem that mits. projos often have is LEAKAGE from the coolant chambers on the front of the tubes. Modern (last 20 or so years) projo sets use a liquid that is placed between the screen of the projection crt and the lens assembly. The fluid is a lot like antifreeze, and it does 2 things. The first thing it does, (most obviously) is to cool the screen of the tube. the fluid conducts the heat from the phospor of the tube, and onto the chamber walls, which have heat-sink fins. This cools the phospor, and ,allows for a much brighter phospor to be used, allowing the kind of bright, vivid pictures most projos have produced since liquod cooled tubes were introduced in 1983 or so.
But the fluid does another function and that is to actively COUPLE the image from the crt face to the lens a LOT better that empty space would do. In this way, less light is wasted and more is used to produce the picture.
However, sometimes the seals on the coolant chambers of the tubes develop pinholes, and after the set warms up, it can leak out of the seal, and onto the circuit boards below. Mitsibushi sets in PARTICULAR suffer from this problem. The fluid is conductive and will RUIN the circuit boards!! Other brands do this too, and Samsung is currently seeing a lot of the same problem in their newer(2000-now) sets. But with Mits, after about 5 years or so, the circuit boards are NLA, meaning they are NOT available to replace them if you need to!! I know of several 1997-2002 mits. that have been junked because of this!!
Then too, there is the sad fact that mits tubes are not very good to begin with!! While an older Hitachi(1990-2000) will have about a 90% chance of having great tubes, the OPPOSITE is true of mits sets!! ibn fact, I cringe whenI am asked to repair a '90's mits, cause if I can get the original problem fixed, the tubes are probably shot(1983-93 or so), and if it is a newer one -1995-2000 or so) they may be leaking!! I recently saw a 1990 model 61" mits. in the trash in a nice cabinet with doors. I passed on it, as I figured the tubes were toast, as they nearly always are!! IN fact, i can think of only ONE brand of older projo with worse crt's than mits, that was NEC. After about 5 years, those tubes in them were GONE!!
So, the bottom line is "I wouldnt!!" Not an older MItsibushi!! projo!! An older RCA or Hitachi or Zenith from 1994-99 or so would be good, too, most likely, as would a toshiba, jvc or such from that time, but NOT a mits!!