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  #316  
Old 01-24-2015, 02:25 PM
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no the last post says 38.2 and 0 v .

Last edited by timmy; 01-24-2015 at 02:31 PM.
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  #317  
Old 01-24-2015, 02:38 PM
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Ok.... Dammit got excited for a minute....

Ok, So please check the voltage on pin 3, 6, 7, and 9 of 6KA8, V503A.

So Timmy, When you watch TV and the scene changes and goes from light to dark
and the picture blooms out, this is a problem you can easily replicate by turning
the AGC on a normal working tv.... Poorly adjusted AGC often make for a really
bad picture - especially makes them look like they have too much contrast, or
not enough.... It's possible, you have a AGC circuit problem here.... I have not
had that much experience in the AGC area.... Not sure entirely how the circuit
works, so outside of looking at known voltages I'll have to get out one of my
books and do some reading....

I was hoping for a bad ground, but there may be something funny going on
in AGC, and it's driving the 12by7a nuts too.... Gotta do some thinking...

Maybe someone with some smarts on this area has something to say....

So when you take the signal off this tv do you get snow....?

And is that AGC control mounted on the PC board, or metal chassis...?

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File Type: jpg 6KA8-keyed-AGC.jpg (65.4 KB, 6 views)
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Last edited by Username1; 01-24-2015 at 02:57 PM.
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  #318  
Old 01-24-2015, 03:07 PM
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well the agc appears to work properly and so does the contrast. 6ka8 pin 3 22.95v pin7 21.73v pin 6 .702v pin 9 36.2v
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  #319  
Old 01-24-2015, 03:20 PM
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this whole thing is just nuts and besides im sure these voltages are dependent upon the chassis being all plugged into the convergence and yoke and the voltages im sure may depend on where a certain adjust pot is, like contrast ect. these voltages on the schematic , does this mean a working set, with all hooked up ? as crazy as these voltages are it still gave a watchable picture.
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  #320  
Old 01-24-2015, 03:33 PM
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Does that pin 6 voltage match your schematic....?
Mine is not that clear for that pin.....

Yah, I'm not too crazy about the chassis being out and not hooked up to all it's support crew....


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  #321  
Old 01-24-2015, 03:47 PM
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my sams show 2 volts on that # 6 of the 6ka8
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  #322  
Old 01-24-2015, 04:04 PM
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i kind of thought maybe i make a mistake when i recapped maybe reveresing 140v for 160v , i dont know but maybe i should take the time and check, i really dont know.....
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  #323  
Old 01-25-2015, 01:14 PM
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ok heres the latest now, i checked the source voltages and all the voltages are good with the exception of the 160v source and the 140v source. the 160v is testing 129v and the 140v is testing 129v also. i also checked all the high wattage resistors between the different voltage sources, all good . checked the caps and connection for the both voltage sources, cannot find anything wrong here. these voltages are on the IF board, chroma board, and verticle board, all the other voltages are ok. there is a 140v source going to the 6gy6 z demodulator pin 6 but when i pull the tube i then get 140v back in it drops 10 volts. maybe this is all correct and places on the board consume voltage like it is just idling with no yoke or crt connected but i thought i would check my work on the recapping. i am so lost here as to why nothing has been found bad yet.
maybe at this point i should figure the right voltage at the 12by7 by setting the bright pot then check resistance on the pot and make up the difference so that the pot can be at max because if i leave the bright in a specific spot after the voltage was set by the pot and it gets turned then its back to square one. this is so not right to do but what else is there to do, obviously there is something wrong here that is being overlooked, and its got to be a simple but yet a criticle thing going on here.

Last edited by timmy; 01-25-2015 at 01:42 PM.
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  #324  
Old 01-25-2015, 04:24 PM
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the hv starts coming up really high and fast almost the way it is supposed to with the hv pot alittle over the half mark but at the same time the voltage comes around on the 12by7 where it is not right suddenly the hv drops low. so with the 140v and 160v sources not right but low it almost seems that the 2 are related , seems like a short of some kind pulling hv and the 2 sources down together.
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  #325  
Old 01-25-2015, 10:11 PM
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It must be the re-materialization buffer override computer..... I'll get Scotty on it
right away.... He should be able to fix at before 12-Midnight !

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  #326  
Old 01-26-2015, 07:44 AM
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when a disc cap shows on the sams as a 150mmf but the spot for the voltage is blank what voltage would this component be. 150 mmf , would this translate into a .0 something ? if this is 150pf what is a suitable sub..

Last edited by timmy; 01-26-2015 at 08:09 AM.
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  #327  
Old 01-26-2015, 02:36 PM
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Hey, been nursing our old cat for the last few days. Don't have the ability to do much of
this stuff recently.... pf I believe is 12 zeros.... uf is 6 zeros. I would have to check the
book, but I'm pretty sure I can remember that little bit... So yah, if you have something
written 150 mmf then it's the same as pf. 150 X 10 - 12.

Those disc caps are pretty cheap, so I bet most are 600V or better..... Unless marked...

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  #328  
Old 01-26-2015, 06:33 PM
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brightness range video

see better link below. Not sure why I keep doing that (google sign in), thanks for fixing that for me SB.

Anyway I wanted to start with a video showing how my brightness pot works, will follow up with one showing pin voltages and HV regulation. The idea being to see how the range of voltages behaves on my set as a ref to what timmy is getting.

One of the points I was trying to make was there is only really about 1/4 turn of useful range. I finds some sets have better range, I think it has to do with how strong the CRT is. This one takes a couple minutes to get to the level seen in the video. This CRT wil have decent emission per the CRT tester BUT the cut off is just barely ok, I can just barely get it to the cut off line. Perhaps the lack of good cut off control limits the effective range of the brightness pot.

Last edited by DaveWM; 01-26-2015 at 10:12 PM.
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  #329  
Old 01-26-2015, 09:08 PM
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Same video minus the google sign in...


https://www.youtube.com/watch?v=CEux-SWHgvs

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  #330  
Old 01-27-2015, 08:05 AM
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is a n150 the same as a 150 pf disc ? i dont know what the n is for..
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