Sony PTV Model # KP-46XBR25 Video blinking on/off about once per second

Hello: I have a Sony PTV Model # KP-46XBR25 DOP 9/93 in my shop which has an intermittent video problem. When the set is started up from a cold start, the raster is black for about two minutes. Then, the video appears and disappears to black at the rate of about once per second. If I adjust the screen voltage pots slightly up or down (Especially the blue) the blinking on and off will slow or stop completely - but the adjustments to do this throws the gray scale off to an unacceptable tint.Also, the blink rate seems to vary with scene brightness. I have seen similar symptons in late 90s Sony 27-32" Table model sets which had a problem with the screen voltage setting on the flyback being critical or the CRT emission too far off on one color. I read something on the Internet about another XBR Sony having a problem with Capacitor C1737 on the "D" board. The audio and delction and tuning on this set are always fine. I would appreciate some tips, list of parts to check, or scans of some service data on this model. Thank you!

Robert McPherson McPherson Electronics Telephone (502) 367-9324 Cellphone (502) 298-6997

Email snipped-for-privacy@bellsouth.net

Reply to
rm502
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Simple to fix, replace all three picture tubes. The cause is the AKB circuit is blanking the video because one or more of the picture tubes is too far out of balance compared to the other tubes or all three are below specification and the AKB cannot compensate. Given the symptom of the gray scale being way off when the blinking stops pretty much guarantees that the problem is the picture tubes.

David

Reply to
dkuhajda

rm502 is quite right about the pix tubes being the cause, but you MAY be able to "tweak" the EEPROM parameters in the service menu to get a good grey scale, after the G2 screen adjustments are set to stop the "famous Sony CRT flash"! Have you guys ever done a CRT boost on these projection CRT's? If so, have they lasted, & how do they look after pix wise? Sony CRT's in direct-view units look pale, & not so good after a boost, although most customers don't complain, I wouldn't like to watch it after a boost.

I have a Sencore CR-70 rejuvinator, but it only has a socket # 3, # 4. I haven't tried to boost them yet. I ask you guys, is a there a way to "work around" the AKB problem? Iv'e seen info about adding resistors to "tweak" the pix to stay on, even though it isn't as nice a pix, but quite watchable. Sky.

Reply to
Skype_man

quite

Reply to
Charlie East

Thanks to all for your responses:

David: Is CRT rejuvenation a possible remedy for this problem?

Robert McPherson snipped-for-privacy@bellsouth.net

Reply to
rm502

You can try it if you've got a rejuvenator, there's nothing to lose, but PTV tubes generally do not fair well for that.

Reply to
James Sweet

Generally PTV tubes will not rejuvinate but the attempt will cause the flakes to short out the gun.

Think about what rejuvination actually does. It blasts the build up off the guns and into the picture tube. Some of it does not vaporize but falls down. On a regular tube it typically won't lodge in the guns. Due to the position of a ptv tube, it almost always falls down into the guns and causes problems.

The best bet is to adjust the G2 voltages to the mid point between where blinking occurs and retrace lines are visible, then readjust for the best possible gray scale in the service menu. The set is and will be on borrowed time and should be treated as such.

David

Reply to
dkuhajda

" snipped-for-privacy@locl.net" bravely wrote to "All" (18 Nov 05 12:45:37) --- on the heady topic of "Re: Sony PTV Model # KP-46XBR25 Video blinking on/off about once per se"

dk> From: " snipped-for-privacy@locl.net" dk> Xref: core-easynews sci.electronics.repair:348996

dk> Generally PTV tubes will not rejuvinate but the attempt will cause the dk> flakes to short out the gun.

dk> Think about what rejuvination actually does. It blasts the build up dk> off the guns and into the picture tube. Some of it does not vaporize dk> but falls down. On a regular tube it typically won't lodge in the dk> guns. Due to the position of a ptv tube, it almost always falls down dk> into the guns and causes problems.

dk> The best bet is to adjust the G2 voltages to the mid point between dk> where blinking occurs and retrace lines are visible, then readjust for dk> the best possible gray scale in the service menu. The set is and will dk> be on borrowed time and should be treated as such.

dk> David

An alternative is to raise the temperature of the cathode a tad. This provokes more electron emission though it may shorten the heater life. (But who really cares at that point!?) A safer way to do this is to replace the typical series resistor with a NTC resistor. This protects from the inrush but then applies a slighter higher voltage to the heater as it warms up. The calculation of the right value to use isn't too hard and the info can be had from many sources. If there isn't enough voltage from the heater source, sometimes it is possible to wind a couple of wire turns on the FBK core. Just be sure the temperature isn't so high it melts something on the neck. Use just enough temperature to bring back decent emission. This method can sometimes get an extra couple years' life from a marginal cathode.

A*s*i*m*o*v

... Engineers do it to maximum stress loads.

Reply to
Asimov

Good idea, Asimov. Thanks!

Robert snipped-for-privacy@bellsouth.net

Reply to
rm502

Good idea, Asimov. Thanks!

Robert snipped-for-privacy@bellsouth.net

Reply to
rm502

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