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  #46  
Old 10-26-2017, 01:40 PM
EdKozk2 EdKozk2 is offline
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MadMan,
After you reverse the ion trap and reset it, you may find an improvement in the focus. Otherwise everything looks good . Some of the horizontal linearity issues and slight phase shift you mention seem to be inherently common with these Admiral sets. The last three Admiral sets I repaired had some of the same issues.
I just got an Admiral 12X12 this past weekend, won't get to it till next year.
Did your set come with a metal rear cover and metal underside shield ?
The rear cover that came with mine looks it may fit more than one model.
Ed
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  #47  
Old 10-27-2017, 01:59 AM
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Quote:
Originally Posted by EdKozk2 View Post
Did your set come with a metal rear cover and metal underside shield ?
The rear cover that came with mine looks it may fit more than one model.
Ed
Yup, I has cover ^_^ but ty.

Quote:
Originally Posted by bandersen View Post
Black to the base - it's on backwards.
Ah. Thanks. Well. It was like that, so not my fault. Actually now it makes sense - blue for electrons, black for the base.

I flipped it around and it seems to have made no difference in the clarity of the image. Perhaps I should readjust horizontal. However, I had to shove it all the way forward on the neck, touching the focus coil. Which I might move it back a bit so the focus can be adjusted, but hey on the plus side, the focus coil gets to be a lot more straight now.

Idk, how awful would it be to put it on backwards? I'm concerned that in the future if the focus coil adjuster gets bumped, it'll snap the crt neck, what with the magnet butting up against the coil.

Last edited by MadMan; 10-27-2017 at 02:06 AM.
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  #48  
Old 10-27-2017, 12:55 PM
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Can always loosen it to the point where it won't spin or move easily, but will move with a little bit of force.
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  #49  
Old 11-02-2017, 02:31 PM
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"Turning the brightness down improves the clarity of the image, but even with the lights off in the room, the image would be too dark (and have too poor a contrast) at a level of brightness that produces a clear enough image. On the other hand, with the brightness all the way up, though the image is blurry, the screen is pretty damn bright. So... the crt is good, I guess?"

Pretty good indication of a weak CRT... yes you can turn up the grid drive and get a fairly bright image but not good focus, as the "sweet spot" (center) of the cathode is depleted... when you turn up the drive, you are drawing more electrons from off center areas, this is not conducive to good focus. Hopefully, the cathode will improve as you run it longer, or perhaps try to re-activate by running the heater at increased voltage (like 7 to 8 volts) for a few hours.

jr
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  #50  
Old 11-02-2017, 11:15 PM
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Originally Posted by jr_tech View Post
Pretty good indication of a weak CRT...
Well... big surprise, right? I had it running the other day and it seemed better, but like I said, it really seems to get worse as the set warms up, but I'm not 100% sure about that. I'm still going to inspect the focus circuit anyway. Plus I still got that slight shadow, but maybe that's not related.
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  #51  
Old 11-06-2017, 11:42 PM
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Ok. So.

I was thinking (yeah I know, that's my problem right there) if I could increase the voltage going through the focus coil it might focus the picture better. To do this, I used my decade box to put a resistor across the focus pot, and it worked. The picture was razor sharp. Though, come to think of it, I'm not entirely sure if the resistance I added increased or decreased the voltage through the coil. :/

I only had it on there for a minute max, but when I removed it, the picture was blurry as hell. I let the set cool off and it seems to be almost back to its normal level of blurriness.

Did I break something?

Last edited by MadMan; 11-06-2017 at 11:48 PM.
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  #52  
Old 11-07-2017, 01:47 AM
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Things to consider: Current through the coil often matters more than voltage. Most decade boxes use half watt resistors. The average focus coil can handle most or all the B+ current through them so the focus pot often is/needs to be a 10-25 watt resistor to handle the power...If you put a half watt resistor big enough to significantly effect the control in parallel with it, then odds are that resistor is going to see several times it's rating and burn open......
Some time ago I found a sencore 'Big 20' which is a decade box made with 20 watt resistors...It is situations like this and power supply work where that box really shines.

Check your decade box is in spec on the setting(s) you used, and if the setting you were using is out of tolerance/open replace the one in the box, and get a 20W unit the same resistance to use in the TV.
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  #53  
Old 11-07-2017, 02:10 AM
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Quote:
Originally Posted by Electronic M View Post
Check your decade box is in spec on the setting(s) you used, and if the setting you were using is out of tolerance/open replace the one in the box, and get a 20W unit the same resistance to use in the TV.
lol my decade box uses wire wound resistors. idk what wattage but I'm certain they can handle it. Besides, does care about the box, I'm worried about my tv.
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  #54  
Old 11-07-2017, 11:46 AM
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Just to nit pick. It's voltage across the coil and current through the coil. Anyway. you definitely do not want to burn out that focus coil. If B+ in the set is close to what the service info specifies, I'd look elsewhere for a solution.

For instance, the entire focus coil/yoke assembly can move back and forth on the chassis. There are two large screws down at the base that hold it to the chassis and there are slots in the support. It was designed so that you can loosen those crews and move it around. It might not be in the "sweet spot" for this particular CRT.
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  #55  
Old 11-19-2017, 08:59 PM
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Alright I found the focus problem. I spent a good amount of time today going through all the voltage checks - and many of them (~25%) are WAY out of whack. So I sat back and did some thinking, and it occurred to me that I should just do what I originally wanted to do - investigate the focus circuit.

I disconnected the focus pot and big resistor that comes off of it. The resistor is in spec, but I found the pot was open from one end to the other. I took the pot off the chassis, and cracked it open and immediately could smell it was fried. It's still stinking up my room, my god, it's so pungent. If you look at the pic, you can actually see the bit of wire that broke and is now rubbing on the... turn-y thingy.

So there's that. Apparently, my adding a resistor across the pot was actually completing a previously open circuit, and that's why the focus would work properly then.

New thingy is on its way from fleabay already.

This just leaves me with the H linearity problem and hopefully this new pot will bring all the voltages in line, because some of them are really far off.
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  #56  
Old 11-19-2017, 09:24 PM
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On wire wound pots (cough rheostats cough) you can often bridge the open and get the pot usable again.

In that rheostats case, you may need to add series resistance (given a lot of turns look bad) and reverse the ends of the pot so the wiper/rotor does not rest in the bad zone when focus is adjusted. Necessity (or cheapness and poor parts availability) is the mother of invention (but does it have Zappa too?).
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  #57  
Old 11-19-2017, 10:23 PM
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Quote:
Originally Posted by Electronic M View Post
On wire wound pots (cough rheostats cough) you can often bridge the open and get the pot usable again.
My first thought as well, but it's pretty screwed up. You can see a large section of turns aren't damaged, but the ring they're on is wrinkled inwards.
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