Sony Trinitron screen discoloration

[JayGabyBail]

I've just bought a used sony trinitron TV (model KV-27v45), and it's got some serious discoloration going on. There's some bloom or geometry issues too but that's not what I'm concerned about right now. I don't know its history or anything, got it from government surplus.

I'm not sure if it's a magnetic issue with the screen, something to do with the yoke, or damage to the aperture grille. If the yoke is as forward as it'll go, slammed right up against the glass, it's mostly the right colour, but the right side is still green when it should be blue and the top left is still red. Not sure what to make of that.

In case it's not quite obvious, the whole thing's supposed to be blue with white & red text

 

[kellys_eye]

Check the degaussing circuitry first.

 

[JayGabyBail]

Nothing is obviously wrong with the degauss circuit, and it is making that distinctive noise on startup. Could it be the internal coil just isn't powerful enough?

 

[kellys_eye]

Degaussing invariably uses capacitors to provide the 'whump' and if the value has changed (aged - quite a common issue these days) you will still get the noise but not the current required to create the proper magnetic cancellation field.

Can you apply a test card signal (cross hatch) or do you have access to a handheld degaussing coil (fairly easily made - Google it).

If the screen was stored against any source of magnetism for any appreciable period it will either require manual degaussing or a good few 'decent' on/off degaussing sessions to make a difference. I'd go for the manual coil method first as your issue does appear to be rather pronounced.

 

[JayGabyBail]

Okay so after a fair few tries at manual degaussing with a coil I'm not noticing too much of a difference. Pictured are a grid as well as red, green, and blue screens with yoke as far forward as it will go, and a blue screen with the yoke moved back.

It feels like nothing sticks, once the coil turns off everything reverts. I can get a little bit of change at the very edge of the discoloration but not much more than that.

 

[kellys_eye]

Looks like a potential physical displacement of the shadow mask - usually caused by someone dropping the set and effectively rendering it unfixable.

Unless anyone else can offer some input?

 

[JayGabyBail]

Well, looks like that's almost certainly it. Turned off the coil without backing away first just to see if I could get some patterns to stick. Got the screen stuck nice and trippy, then reset the tv and it went right back to looking like the pictures. The set's degauss has been working.


Unfortunately I've only got one spare tube lying around, and although it is a 27" sony, it's got one too many pins. I wonder if I could swap the neckboard too? Probably not.


Waitwaitwait hang on, just realized these little bits of sheet metal hanging off the yoke are magnetic, could they be affecting anything?

No, they weren't. Looks like this thing's going to recycling.

 

[JayGabyBail]

Alright, the metal bits don't make an appreciable difference, looks like this thing's getting recycled.