Don't dump your CRT RPTV! - Page 431 - AVS | Home Theater Discussions And Reviews
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post #12901 of 12906 Old Today, 01:10 AM
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Bob, I kinda ramble in my posts - I'm sorry, I do try to edit a little - and I don't expect you or anyone else to read or respond to me at all so your feedback has been very appreciated.

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Are those the only numbers you can use? Usually FBTs have big long strings of numbers, which is what should be used on an ebay search. Or search anywhere, not just ebay. Many manufacturers of such things may have them and not use ebay. At this point even knockoffs would be better than nothing, and your search may need to go offshore.
The thinking behind the faulty FBT was that adjusting the horizontal size, the trimpot for which is on the power board, would only reduce the horizontal size at the corners *very slightly* and not at the horizontal midline at all. It would also only make this tiny change when adjusted to the maximum. Then, as you are watching a show, you see the horizontal sort of stretch and shrink in those corners, making you question if you are now paying for all of the drugs you did earlier in life. Vertical size adjustment works fine.

I heard somewhere that this can be a voltage clipping problem and that the FBT would be the most likely cause. I did find two resistors on the power board that had burn marks on the PCB at their solder joints when I reflowed the board but they tested fine. Replaced them anyway, no change. Fuses look good, all caps look good. Next step is to trace the horizontal size circuit (I do have the SM) and make sure everything is in spec, I guess.

Originally I wanted to focus on the convergence problem first, but I'm just wondering if this isn't a voltage problem at the root of all my issues. I suppose I should find a way to get a scope over here.

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What do you think is the bottom line of what helped on that CRT ECB issue? Caps being old and dried out? Weak solder joints?
Bad solder joints, no question. You could see that several joints on the green and blue were going even without magnification. The caps tested fine on my multimeter, but I didn't like the way they looked and I had spares.

After reflowing those CRT PCBs, the brightness of green and blue went up significantly. The entire image just seemed to be more vivid and focused.

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I have seen the pincushion circuit be badly cold solder jointed on certain units because it runs so hot. Can't remember which brand I found that on, tho. Definitely check for cold solder joints in the pcush circuit.

That said, that advice is primarily for master pincushion. For just the green, you'll probably have to look at replacing the convergence ICs. They are multiple-channel devices and can go out on certain aspects while remaining OK on others. Same is true for the colors. I would replace the convg ICs before doing anything else on that score.
The pincushion issue is "interesting". I've managed to make iterative improvements to it but not eliminate it completely.

All the colors are pincushioned, but blue and red can be adjusted freely in the service menu and get close to correct. Green is adjusted by a series of six trimpots on the convergence board itself, all of which I scored before touching so that I could come back to stock. Four work perfectly. The horizontal PIN adjustment gets close, but requires being cranked close to it's maximum. The vertical pin adjustment has essentially no effect.

The original convergence amp was unquestionably bad. At the current moment I've got a fully functional (I think) STK-4277-SL from Audio Lab of Georgia in there. I did order a kit from TVrepairkits.com per your suggestion, but they sent me the wrong one. When the correct one gets here, if I haven't found the solution yet, I'll give their amp and resistors a try.

I've reflowed the entire board twice, replaced every electrolytic capacitor, replaced all the large resistors (only the piggybacked one was out of spec), and replaced both voltage regulators. I did everything in small increments so I could attempt to isolate the problem as I went. The next step is checking and replacing all the ceramic caps, especially the ones on the green circuit near the amp heatsink.

I should mention what prompted that second convergence board reflow. One day I turned the set on and was watching something, ten minutes in the pincushion vanished for a few seconds, then stretched back to where it's been. I assumed this was a heat-expansion-poor-contact thing and that I must have missed something. So I gently probed every component on the board and the board itself while watching the screen. No effect noted. Went back and reflowed the joints for the second time. No change. Pulled the amp, checked all the resistors, and then tried another convergence amp, with no change.
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post #12902 of 12906 Old Today, 12:58 PM - Thread Starter
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I am glad you are adept in such things. Even I have caused solder bridges in the past just once at a time, so these days I don't touch anything that does not need to be touched. I have been lucky so far, but one owner tried to resolder his Pioneer Elite CRT PS board, saying he was a tech by trade, and left 2 bridges in there. Even I missed the second one first go round, but finally caught it. Unfortunately one of them - or maybe the combo - must have taken something out, because now as soon as it is turned on it starts into runaway screen voltage on all 3 guns; starts slow but ramps up and after a minute or 2 they are so lit up with background gray that the set shuts itself off. Fortunately the protection circuit didn't get compromised. But we don't know what did, and for now I have kicked it back into his court to find where D218 is, as it being directly shorted is where I found the second solder bridge. It's OK and the 100 ohm resistor in series with it is also OK, but something got damaged by those 2 solder bridges being still there when it turned on. Its auto regulation circuit is toast.

That said, I can't wait to see your finished set!

I looked at the pix, and your entire vertical pincushion is disabled, offline, non functional. It's not just the green, it's the master vertical pincushion. If it were just the green, the green image would be separated from the purple image. It's not. If it were a failure of the entire convergence sys, the blue and red images would be all over the place - mirror imaged with each other but neither corresponding to the green.

The entire picture is pincushioned in at the top and bottom meaning that whatever controls all 3 is what's at fault. As such I doubt it's your convergence, unless there is a master convergence register for vertical pincushion. Pioneer did not do what Mit did and make the blue and red follow the green automatically, when in geometry mode. If it were in the convergence there would be separations of the 3 images, but all 3 are still tightly together even tho vertically pincushioned.

b

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post #12903 of 12906 Old Today, 01:50 PM
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But figuring out which one it is, is the challenge! Repairs on panels needing repair usually exceed the cost of replacing them these days.

If your set is perfectly operational, someone should jump on it. An old analog 27" DV is no comparison, as it won't even be HDready!

Tho I must say my 26" Mit direct view CRT in the bedroom continues to deliver excellent, lifelike colorations, excellent grayscale and a nice crisp picture for before-bed viewing, every night. It's at least 20 years old and still hanging in there with never one problem, and due to my calibrating it many years ago it still looks better today than the day I bought it! I keep the Contrast at 40% - have to readjust that back down every time there's a power outage at the house, because it defaults back to max when the power goes out - and the brightness exactly where it should be - blacks are crystal clear black with more than enough shadow detail in the mid grays to be consistently effortless viewing - and I would not want to part with it. I am about 7' away, eyes to screen, and doubt having an HD set of its size at that distance would ever make a difference. Closer up maybe, bigger maybe, but that size at that distance - nada.

b
No bites. Most looked at the big box size and decided it wasn't for them or anyone they knew. A couple weeks back someone inquired on NextDoor.com if it was still available because the TV in their daughter's bedroom died and they wanted to get something she could play games on. Obviously a 53" didn't fit the bill.
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post #12904 of 12906 Old Today, 02:12 PM - Thread Starter
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That old 27" analog TV would have been perfect!

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post #12905 of 12906 Old Today, 03:44 PM - Thread Starter
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The first two are of the final solder bridge I saw and corrected. The third one is the corrected solder joint without the solder bridge. This is the way it should be.

I know the first 2 are a bit hard to see, but trust me, I did a continuity check on it, and D218 was fully shorted. Which saved it of course, it checked out fine once at last picture status. But that diode being shorted took out something downline from it, causing the Screen voltage runaway and making the set unusable now, until corrected.

This was done by an owner who declares himself a tech by trade, and it happened even to him. If you are not a thoroughly seasoned and experienced technician or solder person - like you work at Tektronix and solder every day, like I did before I became a service tech - I advise you to NOT try this yourself. As I have said before, there is far too much riding on it. Send it to me and have me do it.

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post #12906 of 12906 Old Today, 05:17 PM - Thread Starter
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This is the other solder bridge the tech left, not easy to see. Can you spot it? Pix are before and after clearing it
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convergence , Panasonic Tc P65v10 65 Inch 1080p Plasma Hdtv , Pioneer Elite , pioneer sd-p5181-k , Plasma Hdtv
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