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I have to replace some ic's for a convergence issue in a rear projection unit for a friend. How do I clean the power from the high voltage wires? The unit will have been shut off for about two and a half days for bleed down. It is now unplugged from ac power as well as from all other cables. Although I fiddled with tv's in the past and never had a problem with the high tension leads to the picture tube, I just want top be safe and sure this time.
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high voltage
if you have a high voltage probe with a self contained meter, use that to discharge the static charge to a good earth ground on the set. once its bled down, use a crocodile clip between the aquadag coating and earth ground and leave it connected. don't forget to remove it when you're done. you don't want to burn up the voltage tripler. -
Removing electricity....
Uh....I'm at a loss as to most of what you said, HayZee. I think I got the part about a high voltage probe, but I do believe I do not have one. Oh yeah, I do understand the crocodile clip you mentioned. After that I'm a lost puppy. What's an aquadag coupling and what's a voltage tripler? Could I cobble a home made probe to use to bleed the static charge? The only meter I have is a standard vom. Although I do have a one of those lights that go between a coil and spark plug that will glow if the plug fires. That will take over 60KV. Could I use something like that?Comment
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high voltage
well I figured if you are servicing a tv receiver you knew what you were doing. ICs are only part of the operating components of a tv. each one of your color guns is a vacuum tube just like a regular tv tube [screen] each gun has the same components as does a regular vacuum tube except for the aquadag coating. on a regular tv picture tube, the "bell" part has a graphite coating inside that operates at 27-32 thousand volts. the connection to this coating has a recessed "jack" if you want to call it this. a high voltage wire - orange or red in color connects here with a simple thing that looks like a paper clip under a rubber grommet. take a jumper cord with crocodile clips on both ends. connect one end to the metal part of the tv [called a ground] connect the other end to a narrow, well insulated screwdriver and work it under the rubber grommet until you hear a snap. you may not hear the snap. what this is doing is bleeding off the high static charge of the tube. each of the color guns has one of these, so you'll be grounding each one of them. the high voltage wire comes off high capacitance capacitors in the power supply. all tube type tv-s has a high voltage power supply. early ones had something called a flyback transformer. newer ones use a voltage tripler to generate the 27-32 thousand volts. the electron guns of the picture tube, in your case each color gun, shoots electrons towards the front of the tube. electrons that are stripped off have to go somewhere, that's where the aquadag coating comes in. the coating attracts the spare electrons and grounds them out. the "plate" of a vacuum tube attracts electrons given off the filament or cathode of the vacuum tube. the plate operates at or above plus 180 volts or higher.Comment
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bleeding power...
Well, I know what I'm doing....to a point. Maybe enough to be dangerous. I have played with the old tv's while a young kid and did know about the high voltage wire to the tube needing 'grounding' to be safe and that was the process I used. The situation now is that a friend has a projection tv that has a convergence issue. We purchased the repair kit for it and, along with the great instructions that came with the kit, plan to do the repairs ourselves. Since I'm the one with soldering experience and the tools to do it, I'm the one elected. The kit consists of two sizable ic's, a nine pack of resistors and two pico fuses. Not afraid of it, I have done minor repairs to circuit boards in the past, but the instructions said to make sure those leads were discharged. Having never worked on a projection tv before I wanted to be sure the process was the same as the older tv's. As usual, you have taught me, as well as helped me, in my many projects. Thanks, Hayzee.Comment
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Removing electricity...
Well, the job is done and I was pleased that I did have to remove the high tension leads. However...
I did replace the two ic's. No other components needed replacing in this kit. The resistors and pico fuses all read good. The bad news is that, after 76 dollars for the kit, it did not fix the problem. Still experiencing the double green, which is not adjustable using the remote. So, now it's on to some other studying to find why the green is doubled beside itself. Rats. Was hoping for more success than this.Comment
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convergence.
convergence has to do with where the guns focus on the rear mirror. you need to have a "burst scope" what this does is generate the red, green and blue lines that hit the mirror. you can also short out each individual color so you only display two colors. around the guns you have convergence magnets. these are magnetized circular rings that bend the "colored electronics" for loss of a better word so they hit thescreen at the same time.Comment
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Convergence magnets...
Thanks, HayZee. By your description of how those guns work it sounds like that is not the problem. Here's what's happening: Since there is a tremendous amount of 'blurriness' I eventually checked the convergence. I saw what appeared to be a lot of fuzzy there. I moved the red off to the upper right and moved the blue off to the lower left. The remaining, unmoveable green is actually a double image! There are two 'plus' signs that slightly overlap. It's impossible to line the red and blue up on the green as there's always a halo of green. I then set the unit to factory default and found the red and blue are set perfectly over that green 'plus' sign that is at the lower left. That leaves the other green image that is slightly upper right to muck things up. Going back to the picture shows the green halo to the right and top of all images. Printing is very fuzzy as are all images, because of that added green halo. I should also say that at the time of setting to factory default the resultant overlapping of the three colors was a brilliant white. The issue appears to be solely around a second green image that's slightly to the upper right, yet still overlaps the primary green display. The base 'plus' signs of all three colors appear to be same length in both directions, leading me to suspect the focus would be correct. So, that's where I'm at at this point.Comment
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rear projection tv
food for thought - I have a MAGNAVOX rear projection tv in my house. My picture took on the fuzziness you describe. It also took on a yellowish image. I read in a tv forum that these tv's, over time are prone to algae. Yeah that's right ALGAE inside the color guns. Inside each color gun there is a syrupy mixture of ethylene glycol, clear anti-freeze. This is used to cool the tubes. When algae builds up inside, the image blurs. The only recourse then is to replace the coolant. The tubes are mounted base down in a bracket with two seal rings. There is a port to remove the fluid and refill through the same port. If you check some places, I'm sure you'll find the glycol coolant. It comes in a quart container. once you replace this stuff, you automatically have to do a convergence alignment - because the tubes are moved.Comment
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Engine coolant.
WOW! The things learned going from here to there. I'd never have thought there needed to be a coolant in a tv. Although I guess it's understandable, since there's cooling kits for high clocked computers. Will have to do some more mulling over on this. I've been working with the an on-line tech who first suggested the convergence kit. Am also working with the manufacturer of that and other kits about this problem. No surprise....I've learned more from HayZee than from the on-line tech!! Hopefully I can get that double plus sign issue resolved. Everything else about this unit is great except for that.Comment
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Engine coolant??
Ideally in a color receiver the green gun is the prominent one. when all other colors are superimposed over one another the resultant color is white. Do you remember back a ways ? The Heath Schlumberger Company? They made "Heath-Kits" Well I built a Heathkit color tv as part of a course that DeVry sponsored. I had three boards, one for each color. There was a special part of the menu called convergence. You'd slide a switch and a convergence screen would pop up. there were crosses on the screen nine or twelve of them. The coarse adjust were the tube neck magnets. The fine tuning was a convergence board that had 16 adjustable resistors that varied the voltages on the convergence magnets [electro-magnets] on the tube neck, in back of the deflection yoke. the deflection yoke lit the screen up vertically and horizontally. Then you had the vertical oscillator and the horizontal oscillator. The vertical was set for 60 cycle, the horizontal was the scanning lines 525 of them.Comment
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Heath Kits...
Oh yeah! I remember Heath Kits. I had always wanted one, but our family didn't have funds for stuff like that. But I did manage to play with more than my share of the black and whites and then advanced to the color floor consoles. On those I found I could change brightness, size, and even tilt the screen! Played with the color lines, too. The closer to overlap, the brighter the white. All by fiddling with stuff on the tube neck. Still consider myself lucky not ever having been zapped. I envy you doing that Heath Kit TV, HayZee. Sure wish they were still around. And that's what's bugging me about this unit. The red and blue are just as sharp as can be. And even the green is 'sharp', in that it's the same length in height and width. The only issue is the additional green bar that slightly overlaps the primary green. No fuzziness in either one of them. Sharp enough edges to both of them. It's just that there's two of them and the secondary is slightly above and to the right. But it is sharp! I'm really enjoying this learning experience.Comment
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