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KP-57W40, falls in s/n: 90xxxxx, bulletin & questions.

J

Jason D.

Jan 1, 1970
0
I have this Sony KP-57W40 (March 2002) here for estimate to replace
the blue CRT, intermittently shorting G1 (tapping will do this also)
to kine and telltale darkening brown in neck where gun & pins are.
Need to know is this required to change out other green and red CRT
which are working fine and did not have darkening neck like the blue
is?

I have the bulletin sent in from our supplier but didn't say about
this 1 or all CRTs swapped? Second, the part number for green is same
CRT assy for 51W40 and 57W40? Wanted to be very *certain*.

Anything else?

Thanks & cheers, Wizard
 
J

Jason D.

Jan 1, 1970
0
Hate to top post, I'm waiting for your comments on whatever to replace
just one CRT or do all?

Thanks & Cheers, Wizard
 
M

Mark D. Zacharias

Jan 1, 1970
0
Jason said:
Hate to top post, I'm waiting for your comments on whatever to replace
just one CRT or do all?

Thanks & Cheers, Wizard

I'm pretty sure the blue tube is unavailable anyway - they ran out of them
because of all the failures, and their CRT manufacturing plants have shut
down.


Mark Z.
 
Question and comments.

First, in the newer Sony RPTVs I see alot of green CRTs getting weak.
We give it a shot at rejuvination, but the greens don't seem to hold
up. We play them for quite some time, long as possible. Alot of times
they never make it out the door.

I have now rejuved a blue for the first time, and it did something I
never saw before, it came through a life test with flying colors
(figuratively). Not knowing just how much Sensore cuts the filament
down, I did my own life test. Which is to turn the tester off for five
seconds or so, and not disturb any bias controls. Leaving it in the
read mode it came right back up immediately. I mean not even waiting
for a warmup. I couldn't believe it, I turned it off for longer,
perhaps closer to ten seconds, same thing. The set plays wonderfully
and has not had a single arc or even a snap.

Now I have the following observations : When you rejuve the green it
usually does not hold up, also it goes through a snapping/arcing phase,
and then dies a slow death over the next few months. I have seen more
blues get the G2 leakage.

With all this I wonder why. I know one thing different about the blue
in RPTVs, the fact that Sony defocuses the blue in some RPTVs. Could
this be a factor ? The green is of course as sharp as can be, but youi
lose that when you rejuve it. Focus is not that big an issue with the
blue, in fact the last one I worked on had no SVM coil or beam shaping
magnets on it. I can see why.

Perhaps a slightly different G1 aperature size or some other factor, or
like that it is defocused causes cloggage of the hole in the grid. That
cloggage would have to come from cathode coating material, unless the
evacuation and bombardment procees didn't go right during manufacture.
We can only also speculate on why these tubes seem to want to get G2
leakage to a more positive electrode.

This common G2 leakage is probably to G3. I will probably eventually
come up with a good clamping solution to fix it, but the problem will
be when and if the leakage gets worse, and pulls down the G3. Unless
someone thinks it's coming from the anode, I am going with this theory.

Now your problem is G1 to K which is dealt with in a different way. Put
the tester away and get you a 22/150. If you want to be on the safe
side use a 10. Charge it to 100V and apply it to the G1 and K.

Of course you only do this after you have tried a very light
rujvination, rejuvination is a subtractive process (says Sencore) and
if you subtract the protrusion in either element that shorts when it
expands, you got it. Use the strongest rejuve level your tester has,
but just tap the button. That will minimize damage to the good part of
the cathode.

If you do this to the green or red you should readjust the beam shaping
magnets, but with a blue, forget it. It might not even have them
anyway. I don't have one in front of me right now.

One last observation, I rejuved that blue, and then had to turn the G2
down to at or near it's factory setting, when I do a green I have to
turn it up. Perhaps this is an indication of how long the tube will
last ?

Also, when you do the rejuve, not only do what I said, put the machine
on it's highest setting, but you only tap the button. Like a very short
horn honk. Like when you are not pissed. Tap it only. Then you must
switch it to check for G1 shorts. Vary the filament voltage and watch
the indicator. Tap with a screwdriver handle on the neck and watch the
indicator carefully. Do this at high and low filament voltage. If the
tests come up clean, ship it. If you get the slightest little flash or
reading of leakage, consider hitting it again, again, oonly a tap. It
is removing material and there ain't that much.

If you get the G1 short at lower filament voltages, you might want to
reduce the filament voltage during rejuvination. Most testers crank it
up during that function, so keep that in mind too. But then it might
work better at a higher temperature, that would have to be your call. I
would have to be there and see it myself to make the best judgement.

A G1 short is not always the end of the world. Frequently yes, but not
always. At some point it becomes 'what do I have to lose ?'. If the
customer gets another year out of it, great.

When the rejuve is successful in the case of a short, it usually lasts
longer than if it was rejuved for being weak.

Slide that two cents under the door. When the vestibule gets covered,
I'm going to pour a bucket of clear stuff all over it and have the
coolest floor in town.

JURB
 
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