Sony PVM-1270 Purity Issues

[colorfixer]

I picked up a Sony PVM-1270 that someone attempted to replace the CRT, but without a manual. It ran, but the convergence, landing and purity was less than optimal, to say the least. Pulling the cover I found the static purity ring assembly, and even the deflection yoke out of place, and a whole lot of stick on magnets taped, siliconed, stuck all over the place.

Removing these "aftermarket" items, and placing the purity ring assembly where it should have been, I ran through a typical setup: position the deflection yoke, the purity yoke, and twiddle the purity rings for best single color rasters, with little problem. I then did the static and dynamic convergence without a hitch. Everything looks good at this point.

Letting the set cool off for a couple of hours, and powering it back up on the bench I now have purity issues in the top left and bottom right of the pix. I can manually pull it out with a magnet, but it will return with degausing either manually or with power up.

Any ideas? The thumbscrew on the top/back of the deflection yoke changes this, but I can't make it go completely away.

[kx250rider]

Sounds like the degaussing circuit might be doing something weird. Try unplugging the degaussing coil, and manually degauss the tube. Then cool it off, and see if it still goes wrong. If not, you need to check the degaussing circuit, starting with the 3-legged thermistor. Those can either get bad solder joints, or go internally bad. You can get one out of most any color TV from the 80s or 90s, if you need.

Charles

[Zenith26kc20]

The magnets that were glued to the bell of the tube are additional purity magnets. They were installed at the factory. If you have them, after fixing the degaussing circuit, try placing them (one at a time) back where they were. It takes a bit of patience (and turning the air blue) to get them right.
I have used the two lead degauss themistor in place of the three lead. You have to find which two leads are AC. The third lead on Sony TV's go to AC neutral (most of them) and it gets the degauss out of the circuit quicker by heating it quicker. They do, as mentioned earlier, have problems with solder connections.
You may want to check the vertical IC on this set as it is prone also to bad connections underneath. If you have a ESR meter, check caps in vertical and in tuner power supply as well as standby and relay drive. They dry up and lose capacitance, blowing the vertical IC or making the set go nuts.

[colorfixer]

The magnets were definately added after the fact. Sony wouldn't use scotch tape, clear silicone or hot glue.

The original clear plastic strips with the magnets on the bottom were stuck to the inside of the case by the fool who attempted to swap the tube. Were it not for the fact that the tube is new, I'd probably have saved a whole bunch of time performing the lineup but once I figured it out its relatively simple.

On a whim, I pulled the tube, degaussed the hell out of it, then gave the metal funnel the once over in an attempt to appease the gods.


I'm leaning toward the degauss coil. I've unplugged it and letting the thing cool down before I claim victory. I recapped the deflection board since I had everything apart, and wasn't disappointed to find quite a few bad caps, even for a very clean interior.

Once setup, the thing makes a really cool pix on the super fine pitch 330YB22.
The tube has a label marked "EBU". Does this indicate the phosphor type?

[kx250rider]

Originally Posted by colorfixer

The magnets were definately added after the fact. Sony wouldn't use scotch tape, clear silicone or hot glue.

I hope it wasn't dropped, and those magnets added to compensate (half-assed) for the shadow mask being bent. I put thousands of magnets like that on tubes after the Northridge Earthquake, and it works as long as you disable the degaussing coil. I did that in many cases for fallen TVs where the TV owner wanted to pump a few more months out of them, and didn't want to shell out for a new tube.

Charles

[colorfixer]

No, wasn't dropped, worse: attempted repair by less than competent tech.

The issue was a combination of poor yoke positioning messing the beam landing, plus the degauss circuit leaking about 30v. I bit the bullet, pulled the coil, redid the beam landing after manually degausing the entire chassis and completed the alignment ritual. Once I swapped the posistor, the issue is gone.

BTW: I found 4 more cut up fridge magnets between the yoke and the bell. Some even had their original advertising on them (ford dealer).

[freakaftr8]

Sony's use a special pre cut double sided bond for those, Ive seen them in a few up here. Have you found the 3 rubber wedges laying on the chassis? I have seen the top ones fall off causing the yoke to sink down bending and distorting the raster. I have found Sony tubes to be quite finicky when the wedges are removed and the yoke is pushed up against the back of the CRT without that 1/2" gap.

[old_tv_nut]

I would think Trinitrons would either not suffer, or be destroyed by dropping, since the "shadow mask" is made of wires under tension.

[andy]

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[colorfixer]

I've seen the same issue, as well as what happens when someone tried to use a really strong degauss coil on the face of a trinitron. It literally ripped the wires off the grille.

google "trinitron lines" You'd think that they'd be a bigger problem than they are.

In response to freakaftr8, one wedge which the "tech" attempted to silicone onto the tube was still there, the rest had the adhesive turn into a slimy goo. I cleaned the old glue residue off and used a new strip of nitto double backed adhesive tape. This stuff is gold: think of two thin layers of glue sandwiching a thin layer of fiberous paper. I also use it to stick on those stubborn metal sony badges, as well as mylar keypads.

[freakaftr8]

Yeah, iv'e ssen that bonding turn into slush from smokers houses..