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post #12901 of 12902 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.

Originally Posted by Mr Bob View Post
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.

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.

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 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 12902 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 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, 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 vertical pincushion is disabled, offline, non functional. It's not just the green, it's the master pincushion. If it were just the green, the green image would be separated from the purple image. It's not. The entire picture is pincushioned in at the top and bottom meaning that whatever controls all 3 is what's at fault.


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