Need schematic for Sony KV-1380R TV

"hr(bob)

An intermittent short in one could affect the pic size like you say.

..... Phil

Does the picture brightness remain the same?

Sylvia.

Check for a bad 33uF 160 volt capacitor in the power supply.

Mark Z.

Yes, the brightness does not change. So far today the picture has been ok every time I looked at it.

So far I'm monitoring the output of the rectifiers on the AC power line. If that voltage stays ok when there is a failure, I'll go to the output of whatever regulator there is and start looking there. The problem today is no failure at all. Hate intermittents!!!!

Yet wouldn't one expect the brightness to increase noticeably if the size decreases by 20%?

Sylvia.

On Sun, 27 Dec 2009 21:54:47 -0800 (PST), "hr(bob) snipped-for-privacy@att.net" put finger to keyboard and composed:

It sounds like the EHT is increasing substantially. Does the set have separate horizontal deflection and EHT generation circuits? Is there a H-stat?

- Franc Zabkar

Would also make the image brighter, wouldn't it?

Sylvia.

ly

Sylvia:

It might, it is hard to tell if the image gets brighter since I have never actually seen it make the transition from normal to shrunk.

Franc:

I will put my HV probe on the CRT HV cap and see if it varies. It must be going up quite a lot to make that much difference in the picture size. From my old TV days over the past 54 years, it is almost always the reverse, the HV goes lower, and the picture gets dimmer and noticeable bigger (blooming we call it on the west side of the pond).

Perhaps get a video camera and recorder on it? Would also tell you whether the change is abrupt, or somewhat gradual, which you presumably also don't yet know.

Sylvia.

On Tue, 29 Dec 2009 13:36:17 +1100, Sylvia Else put finger to keyboard and composed:

Yes, I would think so.

As for the effects on H & V size, if the set generates the EHT from the line stage, then I'm finding it difficult to comprehend how the size varies proportionately in both directions.

If the B+ were to increase, then the horizontal deflection current would also tend to increase. However the vertical deflection current should remain unchanged because there is a low ohm, current sensing, feedback resistor in the yoke circuit. At the same time, the EHT would increase and the raster would shrink.

AFAICs, the width should be far less affected than the height.

- Franc Zabkar

What I had in mind when I asked the question I'm finding it difficult to express properly. If people will allow me some lattitude in terminology then, it seemed to me that some TVs, at least, contain a digital processor which, amongst other things, allows control of the picture size from a maintenance menu. If that processor was getting confused about how big the picture should be - e.g. a digital bit has gone flaky

- then it could be adjusting the image size accordingly, but also adjusting the beam current to maintain constant brightness.

Thus it seems to me that whether the brightness changes is an important symptom.

Sylvia.

My money would be on the STRXXXX voltage regulator that most Sony's of that era had. They are a common failure, although they usually do go intermittent. Andy Cuffe

snipped-for-privacy@gmail.com

Only

good point!

Today the picture had shrunk when I went to my workshop. The rectified line voltage had risen to 150 V from 140 V when the picture was full-size. This might be due to a decreased load on the power supply since the scanning current has gone down. Next thing to do will be to see what if anything I can do about turning the set off and on after a failure and see if the picture restores to correct size or not. This seems to be a bottom-line Sony, so I don't know if there is anything adjustable from a memory chip that might affect the picture. I am also going to move my voltmeter to the CRT cap and see what the HV does when the failure occurs. Stay tuned!

This unit doesn't have adjustments stored in a EEprom. Mark Zacharias' solution is the most common failure mode causing this symptom. Rarely the STR IC goes intermittent and even rarer, a resistor changes value in the regulator circuit. I'd replace the 33 uf cap he mentioned before further troubleshooting. Chuck