CurtPalme.com Home Theater Forum

[Curt Palme]

Here's one for the techies. Sold a low hour late model Runco DTV 947 Barco 708) to a planetarium to replace a dead set. It arrived and worked fine for 2 days, then the HV wire to the blue tube arced. They shut the set down, and I told them to disconnect the blue HV lead from the splitter, and the other two tubes worked.

Since they were in a bind, I had them take the blue tube out of their 708 and drop it into my set to get them running.

Everything worked, but the blue image was almost twice as wide as the R and G, that were still aligned properly. The blue crosshatch was fine, no irregularities seen, but it was way too wide. Height was fine. THey swapped deflection boards, still the same problem.

I had them swap the H yoke leads between the G and B tubes, and the problem stayed with the blue. Had them disconnect the convergence yoke 'just in case' and no change. The blue was still too wide.

That left the yoke. they swapped the yoke from their old set, and that cured it.

Now, my fellow techies, what went wrong in the yoke to cause this? Any time I've seen a yoke with shorted windings, I'd get an H lin irregularity somewhere in the image, or the yoke would smoke (back in the tube TV days).

The schematic shows one single coil winding, no resistors or capacitors in the yoke itself, but I suspect that there might be.

BTW, the HV most likely shorted to the yoke. I still can't figure out what happened. I am getting the yoke back, so I will find out...

[Curt Palme]

Here's one for the techies. Sold a low hour late model Runco DTV 947 Barco 708) to a planetarium to replace a dead set. It arrived and worked fine for 2 days, then the HV wire to the blue tube arced. They shut the set down, and I told them to disconnect the blue HV lead from the splitter, and the other two tubes worked.

Since they were in a bind, I had them take the blue tube out of their 708 and drop it into my set to get them running.

Everything worked, but the blue image was almost twice as wide as the R and G, that were still aligned properly. The blue crosshatch was fine, no irregularities seen, but it was way too wide. Height was fine. THey swapped deflection boards, still the same problem.

I had them swap the H yoke leads between the G and B tubes, and the problem stayed with the blue. Had them disconnect the convergence yoke 'just in case' and no change. The blue was still too wide.

That left the yoke. they swapped the yoke from their old set, and that cured it.

Now, my fellow techies, what went wrong in the yoke to cause this? Any time I've seen a yoke with shorted windings, I'd get an H lin irregularity somewhere in the image, or the yoke would smoke (back in the tube TV days).

The schematic shows one single coil winding, no resistors or capacitors in the yoke itself, but I suspect that there might be.

BTW, the HV most likely shorted to the yoke. I still can't figure out what happened. I am getting the yoke back, so I will find out...

[Mark_A_W]

Well, a shorted yoke would have a weaker magnetic field wouldn't it?

So the image would be deflected less, narrower not wider...


Makes no sense.


Moving the yoke backwards makes the image wider, could that have happened?

[Curt Palme]

No, as his V height stays the same. Ultra ridiculous...

[Curt Palme]

No, as his V height stays the same. Ultra ridiculous...

[macgyver655]

A short in the winding maybe causing an increase in the horz current which may cause the increased horz size. Is the size increased about the same on the left and right sides? Or more on 1 side?

[Curt Palme]

I'll post a pix. Usually when I've seen shorted yokes in the TV store back in the day, there'd be some foldover or similar. Nothing here, just 50% more width.

[Curt Palme]

I'll post a pix. Usually when I've seen shorted yokes in the TV store back in the day, there'd be some foldover or similar. Nothing here, just 50% more width.

[macgyver655]

Well I would think that depending on just where in the winding the short is would determine what the anomaly in the screen would be.

You know its the yolk so what could cause the field to increase?

If there is a hidden component in there like you said and it has changed in value, sure.

If no components then what? Unless the wire size increased from the arc (hahaha) then whats left is increased current creating a stronger field.

Unless the yolk is now ob-longed instead of round....... again, hahaha.....but a little less....ha.

[macgyver655]

Hey, I just happened to think. When they were first changing the tube and they removed the yolk from the bad tube to put it on the other tube....... did they drop it? If so then the ob-longed theory comes into play.