#16
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Vertical and horizontal lock are still very poor, and definitely degrades as the set heats up. Have been swapping out tubes, but none seem to make a significant difference. Even changed HZ output and damper just for grins and no change at all. Brightness is getting better, but hold is bad. It loses vertical when changing channels on the DTV box and even when a show cuts between scenes it can lose vertical. https://youtu.be/Pgm-8XGRZq0 I unfortunately don't have a HV or CRT tester or pattern generator. I'll check eBay and see if there's something available that won't break the bank. I've been checking voltages and the third B+ (should be 130V) measures around 117 though the higher two (240 and 210) are dead on. I've changed the power resistors and all of the filter caps are brand new, so something is dragging it down. Also noticed that the AGC control on the back has absolutely no effect at all on the picture. I guess I'll start focusing there and see if maybe there's a bad resistor hiding out or something, since at this point all of the paper caps have been changed. Big progress since day 1 though! Thanks so much for all of the suggestions! FK |
#17
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If both vert and horiz stability are bad, and the caps have been replaced, I'd look for a drifted or open resistor in the sync separator circuit.
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#18
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I was noticing the certain voltages were still low, such as the CRT screens and the boost voltage was about 520V where it should be 580. Checking the schematic again I realized there were two caps that I didn't mark as replaced which turned out were in the HV cage (duh). I carefully took it all apart, replaced the caps and carefully put it back together and.... no HV. Took it all the way apart again, triple checked the wiring and joints, carefully put it all back together and... still no HV. Verified DC resistance all the way across the flyback, resistance between the grid caps of horiz output and HV rect were both spot on schematic. Ultimately, it appears that in the jostling around, the filament of the HV rect decided to go open - no continuity between pins 2 and 7. Tried touching up the pins, removed the base and tested directly at the leads, but still open. Unfortunately this is the only tube I do not have a spare of, so at a small pause. Before all of this I did experiment with the brightener and it did make a difference in terms of overall brightness however the contrast was still very washed out. As in, adjusting brightness/contrast it went from dim gray on gray to saturated white on white. Possible if the caps I did replace could have been causing this? (attaching snippet of schematic) Thx all! FK |
#19
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Well, I've learned that apparently you can't test a 1B3 tube's filaments with an ohmmeter, and apparently my tube tester also cannot test a 1B3 tube so entirely possible that my diagnosis could have been inaccurate.
I went back and did a few more checks and found a few more out of tolerance resistors and one that was open and decided to give it another try. This time, HV did come up briefly but it started arcing after a few seconds. I took the HV cage apart again, even coated the leads of the new caps with corona dope, quadruple checked everything put it back and same thing. https://youtu.be/mxDbkEfzzWA The camera doesn't pick it up very well but the buzzing is accompanied by blue-ish flashes in the HV tube. From what I've read, blue means the tube is gassy, but everything was working fine before. Ideas? Thanks! FK |
#20
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Pull the cap off the top of the 1B3 and see if you can draw a nice blue arc to the tip of an ungrounded (plastic handle) screwdriver, if you get a good arc and the buzz is gone then the problem is probably after the tube, perhaps under the base of the 1B3. It could be a gassy 1B3 but those usually just glow purple without any noise.
It's possible you cracked it somehow and completely let the vacuum out, in that instance it might arc and buzz internally. |
Audiokarma |
#21
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"Well, I've learned that apparently you can't test a 1B3 tube's filaments with an ohmmeter"
Huh? I just went out to the shop and measures about a dozen of them ... all were right around 2 ohms, pin 2 to 7. jr |
#22
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FK Last edited by FrankieKat; 08-21-2017 at 10:18 AM. |
#23
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https://youtu.be/Ms4351ADleA |
#24
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What number, or, size is the picture tube? That arc sounds low, but, you never know.
Does your set have a width control, Horizontal Phase, Horizontal oscillator, or, width? My guess is horizontal oscillator troubles. If not, something in horizontal output, of, Damper. Does your set use a hv capacitor on the hv rectifier? Bill Cahill
__________________
"Tubes are those little glass things that light up orange unless there is a short.. Then they light up all pretty colors..." Please join my forum. http://www.tuberadioforum.com/ |
#25
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https://youtu.be/fsLuy2y1dy4 Brightness is still a problem, the above video is taken in a pitch black room with brightness and contrast up almost all the way before the image completely saturates. The brightener increases the overall amount of light produced, but the poor contrast is unchanged. This video is without the brightener. Would also say it looks brighter in the video than in person. The picture is a bit noisy too, but that could be more related to the $20 DTV box that I'm using. Depending on how this all turns out, I might try to pick up a BT Agile for a better signal source. The horiz and vertical lock are solid as long as the station is tuned in properly and both controls are pretty much at their extreme clockwise position. I've subbed out every tube at this point and tested every resistor, and all caps are replaced. The horizontal control is a little bit fritzy so I'm going to try to replace it and see what that does. I purchased an VA62 pattern generator, a CR70 CRT tester and a 1000-1 HV test probe so should soon be able to determine CRT state. FK |
Audiokarma |
#26
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Also, does anyone know what is symbolized on the schematic by the x's and the dashed lines? I had thought that meant a disconnectable connector or the result a switch of some kind, but don't see either of these present. The width control does have an effect on sync, and I have not yet tried adjusting the horizontal oscillator nor the horiz mult trim. The AGC control has absolutely no effect on the picture and I've checked everything I can find between the tuner and the 1st IF and all seems to check out okay. Perhaps it just doesn't have an obvious effect due to substandard signal from the $20 DTV box? FK |
#27
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The x's and dashed lines are SAMs notation for production changes. The solid line circuit is what was the original or predominant circuit. The dashed lines represents a circuit change. So you either have the circuit of the solid line or the dashed line (with the solid line circuit broken at the x's).
No switches or connectors are represented in this manner. |
#28
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Based on that, I appear to have the earlier revision. Good to know! FK |
#29
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The AGC control should allow you to go from blank raster (no signal) to overloaded (negative picture with poor sync and buzz in sound) at full clockwise.
It may be an open control but what are the chances the set is producing a marginal picture and not one of those extremes? That CR70 CRT tester should permit you to see the "cutoff" performance of the CRT, that is how well and linearly the control grid voltage G1 modulates the brightness, and by default, contrast. Those coils between the 12BY7 and the CRT should be checked to see if one is open.
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"When resistors increase in value, they're worthless" -Dave G Last edited by DavGoodlin; 08-22-2017 at 12:28 PM. |
#30
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I'm going to go over all of the AGC circuit again with a fine-tooth comb. I agree it doesn't sound right so it seems like it's the next thing to tackle. FK |
Audiokarma |
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