Mitsubishi VS-466R Dark Picture

I know this is an old TV, but I have had it so long I hate to get rid of it, at any rate I have noticed that the screen?picture has gotten dark and if the room I use it in is to bright I can not see areas of movies that are in the shadows? Any ideas? Or should I just get a new one?

Mike

Reply to
mpo702
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I take it the whole picture is dimmer now. If so it most likely is falling crt emission. Reduced emission is easily fixed by wrapping a turn of wire round the loptf and putting this in series with the crt heater. You'll often find connect it one way round it works like new, connect it the wrong way and it'll be much dimmer.

Its diyable if you're properly aware of the dangers in tvs. The work itself is fairly elementary.

If someone suggests a crt rejuvenator or booster, dont. Those things give a short term boost but really kill the tube's long term prospects by causing heavy smearing. Upping the heater voltage is generally a long term fix (perhaps counterintuitively).

NT

Reply to
meow2222

snipped-for-privacy@gmail.com ha escrito:

you could adjust the SCREEN control on the line transformer a bit, using an insluted flat bladed screwdriver. you'll know its too high if white horizontal lines appear in the picture. worth a try.

-B.

Reply to
b

it could in principle be either of these 2 faults, poor emission or screen adjustment. OPs never give enough detail, and I've given up asking for info as it never comes back.

NT

Reply to
meow2222

We had a salesman who did that all the time. I had a stamp made up which said, "Insufficient Information" which we stamped on his RFQs.

Reply to
Homer J Simpson

I have been restoring and rejuving CRTs for nearly 30 years and have had many successes with the process. It depends on the tube. In this case, however, it is not likely worth the trouble. This set's CRTs often did not respond well to restoration. Some do, some do not. Increasing the filament voltage is actually a short term solution itself and may have little benefit if the phosphors are worn out. In general, this set is beyond its useful life, but the only way to know for sure is to examine the condition of the phosphors and test the emission. Restoration might be worth a shot but most techs would not bother on a set this age.

Boosting the filament voltage with flyback windings is not something that I would consider safe for most DIYers. It is rarely the best option unless there is a HK short.

Le> I take it the whole picture is dimmer now. If so it most likely is

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Reply to
Leonard Caillouet

That would be hard to do since on this set, and most RPTV sets you will not find a screen control on the LOT.

Leonard

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Reply to
Leonard Caillouet

Short lived results from heater boosting wasnt my experience, though it was my initial expectation. In fact those repairs lasted very much better than rejuves, and worked more or less 100% of the time, unlike rejuvenation. I swore off rejuves very early, and used heater boosting. At that time I never came across anyone else using the same approach, they were all doing rejuve, and paying silly money for base connectors for them. And they were all were unable to revive various types of tube, esp Sonys, so I picked up all the old Sonys.

Rarely the bst option? It always worked IME. I'm going to take a guess you've stuck with rejuv and done little or no heater boosting. I'm the other way round.

NT

Reply to
meow2222

Experimented with both increasing filament voltage and restoration. If you understand what each does and why they work or do not, you would find that if there is sufficient emitter material left in the cathode, either can work, but fiddling with flyback winding is a riskier approach. With the better restoration equipment we have had good results on many sets.

If you believe that either method always works, you are making a hell of an assumption. If a tube is too far gone or if the phosphors are worn out, you wont get good results no matter what you do.

Le>

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Reply to
Leonard Caillouet

The 2 methods work in different ways, though both improve emission. Rejuv strips off surface contaminants from the emitter, voltage boosting simply ups the thermal emission of electrons - and this is a process that will work with any emitter material afaik, just a basic physics property. So its hard for it to fail, though not impossible. It isnt going to correct any other tube faults, or deal with shorts, as a rejuve machine can, but it will increase cathode emission. One way it can go wrong is overheating the deflection assembly, but this is rare in practice.

I once did a test case with this method, found a set with emission so bad nothing could be seen on screen, and it was an old sony, famous for not responding to rejuvenation. I pushed it hard, +70% heater voltage boost and IIRC +10% EHT boost. The heaters glowed yellow instead of red-orange. The result was ok performance, and I kept it, since it wasnt fit to pass on like that, and it ran fine for years, no visible deterioration.

When run at rated heater V, not all the cathode area emits. Some is too cool to work. Boosting heater power has 2 effects: it ups the emission of the damaged or worn out areas, and it brings into action more cathode area, the outlying bits that didnt emit before.

I certainly havent been doing it 30 years, but in the time I did I saw inconsistent results with rejuve, which would usually fade again in a few months, and cause heavy smearing when emission faded again. Heater boosting otoh is a relatively sure bet. I'm talking here of 33% & 50% V boosts, not the old fashioned 10% boost, which is of little use.

NT

Reply to
meow2222

Every set that I have tried 10% to 50% filament boosting on deteriorated within months to the point that it was unacceptable. We have mixed results with restoration but many of them stick. The degree to which one calls success may vary with expectations as well. If I can't get good gray scale tracking I do not consider the process successful. Could be that we have only tried boosting CRTs that would not have been acceptable anyway.

Leonard

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Reply to
Leonard Caillouet

I'm quite surprised to hear that, and am wondering why the difference. I dont know.

Yes. I had no problems there, except for the experimental boost set, where the resulting gun matching was way out - but no-one would ever attempt to boost something that bad for commercial reasons.

How have you chosen your boost voltages? Have you just given it enough to look ok, since you mention using as low as 10%, or have you waded right in with 33% for mild cases and 50% for the baduns? The latter is what I did, gives it enough margin to look good for many years to come.

The one type of tube I didnt have good results boosting was ones that had been rejuved. Once that has been done, really its a death sentence. With those, a boost can get you a short term result, but the reappearance of smearing soon ruined things.

when I first learnt of heater boosting I got very much the impression it shouldnt be overdone, but my own experience was pretty much the opposite, that tubes can be hit very hard and consistently survive, and that its underboosting thats unsatisfactory, not over. 50% V boost is a good double the heater power, far outside design margins, yet rarely any problem with it.

NT

Reply to
meow2222

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