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CRT QUESTION/PROBLEM


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I was sent the question below and do not recall anyone having the problem...........comments

 

The touch screen display on my '89 is too high on the CRT. (Top buttons are nearly off off the top of the screen) Is there an adjustment control to lower the display?  Thanks for the help!  Gary ,  Denver, CO 

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Barney,

 

I'm fairly certain there is an adjustment for vertical position of the video image on the CRT, but it is only accessible by removing the shielding on the CRT to expose the circuit board. I would not recommend this to anyone without electronics repair experience as there are dangerously high voltages within the CRT assembly even after power down due to the charge retained by capacitors therein. It would also be near impossible to adjust this with the CRT hooked up in the car, as there isn't enough slack in the two harnesses. It could be done with the CRT testing tool and a 12V bench power supply (how I test and work on my own) but not everyone will have those facilities at their disposal.

 

Further, if the image has shifted that badly on it's own, then there is a problem present; may be a simple matter of a failing component or something else more complicated. CRT drive circuits are relatively complex in terms of establishing correct geometry, convergence and focus. Actually, if you understand what goes on inside a CRT, it is a rather remarkable process of great precision.

 

Since conventional TV repair is a dying (well, all but dead really) art, it seems there will be a future need for someone to continue offering CRT rebuilding. Right now Eddie Voland is the guy, I do hope he stays at it for quite a while yet.

 

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I will muddy the water on this some. My father-in-law repaired TVs as a sideline many years ago. Mostly black and white, which he said were much simpler to repair. I spent lots of time in his little shop watching him and getting a little education on how they work. To move the image on the screen he would loosen a screw on a clamp at the very back end of the CRT that allowed him to move what he called the "Yoke". The  yoke looked to me like a bundle of wires and a round permanent magnet that slid over the end of the CRT. He said it would bend the electron beam to focus it on the front of the CRT as you moved it in and out or rotated it. I don't know if our CRTs are made like that or if they can be adjusted the same way. I do know that he always cautioned me not to touch anything in that area myself because of high voltage produced by what he called a "flyback"  transformer. I'm not suggesting anyone try this. I'm just throwing out as something to think about. Sometimes I drift back into the past and reminisce about the way it use to be.

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I also did some TV repair in High School, Mostly B&W TV's but some color also. The high voltage flyback transformer connects to the back of the tube and its what fires the electrons in the tube. So adjusting the from the back of the tube fired up will be quite

dangerous. If i remember correctly voltages on the TV's were 20k to 40k volts from the flyback transformer. I had a color set once that had the insulation crack on the flyback wire to tube. It arced to chassis ground about 3 inches long, big blue arc. Fixed it with a dab of silicone. 

You might be able to adjust it powered off, You can discharge large caps by shorting with a screw driver.

If it was mine I would send it to Eddie

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I too, just had Eddie Voland fix my CRT.  I'm soooo happy now...it's absolutely perfect.  Best $175 I've spent on the car!

Mine used to get the intermittent "squigglies" (shown below).

p.s.  Has anyone else noticed that if you do a search for "CRT" on this forum, nothing comes up?  Or, am I doing something wrong?

CRT.jpg

Edited by BrentS (see edit history)
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I believe the picture BrentS posted was pre-repair as the middle of the screen is showing some jitter, or the camera caught it in the middle of a refresh scan. As to Ronnie's post, the yoke can be adjusted to correct for tilting (rotation) of the image by turning it until it is horizontally level. Horizontal shifting upwards or down of the image off the edge of the screen will not be generally be adjusted by the yoke position. I suppose if the yoke came loose, and backed partway off the neck of the tube this symptom could result but I imagine other major image distortion symptoms would result as well.

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This is a vertical sweep issue. Definitely a circuit issue. I was an electronic tech back in the day, and usually the height can be adjusted, but I can't remember if there's a HEIGHT adjustment on these Zenith units.

My question is , if the vertical scan is stretched, as in this case, do the soft button functions work?

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Whether the CRT was simply too far ahead of its time, a bad idea or a bad implementation depends on your perspective.  The automotive press views technology warily at best.  Anything too radical is just too much.  The biggest problems with the Buick/GM CRT were education (dealer, media, customer) and the Riv/Reatta demographic not being the most accepting of something as radical as page-organized virtual controls.  Personally, I prefer the CRT Reatta's clean minimalist appearance to the redesigned dash versions but I do understand that others disagree.  

Edited by drtidmore (see edit history)
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I always thought that much of the reason is that the display was not "sunlight readable" and could not be used with the 'vert. Does seem that by '92 GMs digital displays were mostly done.

 

Kids are fascinated that my '88 has a touchscreen, many weren't even born yet.

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When I bought the Reatta new in the fall of '88 our 9 yr old daughter thought it was the neatest car on earth.  She wanted to show all her friends.  Now our 10 yr old granddaughter and 8 yr old grandson seem to have found that same affection and awe even compare to our C5 Corvette and much of that awe is centered around the CRT!  Our daughter has expressed that she would like to have the car when the day for such eventually arrives.

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