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  #1  
Old 06-26-2011, 04:44 PM
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goes out of focus

hey all well i thought i was done but i guess not so here is a question, what possibly would make the screen go blurry from time to time on this ctc15 all caps have been changed now checked into other tubes that may make this do this and tried others including the focus tube. seems after i did the rest of the caps i noticed it. caps in the vert board and the c2 and c3 multi caps were changed with single caps rated somewhat alittle higher. i adjusted the agc and the video peak thinking this may be the cause.so now ill run it awhile and see if its better since adjusting those two. the picture also pulls in on the left about a quarter inch with some scene changes. this seem to have started with the blurry or focus thing after i changed the 8 capacitors which is 4 in each multi cap, i dont know which of the 8 caps between the both muti caps would cause this as each one is for a certain circuit like this focus thing. what is confusing is that the sams says for c3c is 250v 100uf but the cap says on the side 250v 20uf and c3d says 50v 250uf but the cap shows 50v 50uf so i put in what the old caps had on them not what sams show.

Last edited by timmy; 06-26-2011 at 06:12 PM.
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Old 06-26-2011, 10:59 PM
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Check your high voltage at the focus lead and see if it fluctuates.
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Old 06-27-2011, 02:26 PM
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well yes it does fluctuates and its around 640 and turn the bright down and it rises to around 800, the more out of focus the less the voltage and its with white pictures that are bright. it clear its hv regulation but im stumped here as to where to go from here. i tried another 3a3, 6bk4, checked the 6cg7. grid voltage is ok at between 118-120v. this all seen to start after changing c2 and ce caps with separate ones for each with slighty higher uf and or voltage.hv stands at 24kv bright down and the hv adjust pot has no affect when turned.also tried another damper with no result. if its low b+ then why after the caps were changed or is it something to do with the hv pot not working.
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Old 06-27-2011, 02:51 PM
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your focus voltage is too low. Should be 4-5K volts.
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Old 06-27-2011, 03:07 PM
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I would check the whole HV setup. you need to monitor the cathode current of the HOT, the cathode current of the shunt tube, and the HV at the CRT anode.

the sams should run this down. the shunt generally has a precision 1kv resistor in the cathode circuit, a voltmeter across this will will give the voltage drop which translates into the current. should be between .5v and 1.5v depending on scene brightness and HV setting.

the cathode current on th HOT will be around 180-220ma there are adapaters that have leads in them that break the cathode for a ma meter in its place. I like analog meters for this as its easier to see the needle movement. Here you adj the eff coil to dip to the lowest readings.

there will also be adj for the horz osc, shunting off the sync pulse etc...

are you sure you had the focus voltage?. its the pin with the black lead. For it to be that low it would seem there is something big time wrong, esp if the HV is 24kv. the lower voltage sounds more like a G2 voltage
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Old 06-27-2011, 03:19 PM
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maybe its just blooming? seen this when brighness not setup right (CRT bias/G2 screen settings). mostly I see this on my zeniths, if you setup wrong and then have a sudden bright scene change the screen will partialy bloom, go a bit out of focus, then kind of recover.

you could try reseting the entire grey scale and see if that helps.

oh and if you have one, sub in a new video out tube, if its acting up it can mess up the bias of the CRT cathode voltage.
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Old 06-27-2011, 04:39 PM
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the problem here is ever since i replaced caps for the c2 and c3 multi caps with singles this seems to have happened, didnt have any of this befor and i also changed caps in the verticle section for a rolling problem but did not cure that but the set worked fine no blurr or focus problem and the longer it stays on the worse the screen gets. im thinking of putting back the wires to the old caps because i dont think the caps in the verticle section would do this, all the values were right on for that section. which video output tube would that be, video 1, or 1&2 or 2, or 3rd. and the kine bias is all the way down all adjustments were made and the bias did not need to be raised.

Last edited by timmy; 06-27-2011 at 04:49 PM.
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Old 06-27-2011, 06:38 PM
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It would be the video out a 12GN7 or 12BY7 something like that. Its the last on before the cathodes of the CRT. Its plate is connected directly to the cathodes of the CRT (thru the service switch and the drive pots) is sets the voltage of the cathode so if the that tube is not right it will effect the plate voltage, which then effects the CRT cathode voltages (and therefore bias), ultimately can cause the crt to draw too much current, which loads down the HV, which then blooms, and if only slight bloom can look like focus problems.

did you double check that focus voltage? I would use a HV prob so as not to load it down too much. if it really is that low (like the other poster said should be 4-5 kv) then it has to be a problem in the focus circuit, and those filter caps are not going to help anything. I have a simpson 260 analog that goes up to 5kv and use that one as well for checking focus voltage.
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Old 06-27-2011, 06:51 PM
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tried the 12by7 and no change. i had used a fluke dvm and that voltage is what i got so if its going to be 5kv then i would have burned the meter out. i just dont understand what is going on here it was fine befor the multi caps. white screens were worse now its all screens as it has gotten worse.the 700 volts were from the 2 wires of the focus coil . also tried another 1v2 ans 2av2 no luck. i also put a fuse between pin 3-6 of the 6dq5 to ground. maybe the fuse has to much resistance, its half amp 250v.

Last edited by timmy; 06-27-2011 at 06:57 PM.
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Old 06-27-2011, 10:16 PM
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the 4-5kv is what you need at the focus pin on the CRT, you can check that with the same HV probe used on the anode of the CRT.

You need to check there before doing anything else, confirm its the problem.

again, I can't imagine a reason the filter caps could cause the issue, unless something went bad wrong like a reversed polarity (does it use a doubler B+ supply?) causing a major issue with the B+.
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Old 06-27-2011, 11:01 PM
ctc17 ctc17 is offline
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yes the 15 uses a doubler,

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Last edited by ctc17; 06-27-2011 at 11:04 PM.
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  #12  
Old 06-28-2011, 07:52 AM
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chassis is out now looking for problems checked hv pot adjust and all i get out of it is 300k not 500k for what it supposed to be.where is the b+ doubler or what does it consist of, diodes or caps, i really dont mean to sound like an idiot but im trying,lol. from what i understand this set always since i have gotten it going had hv problems because bright up hv is 14kv bright down hv is 24kv seems its not holding hv at 24kv or so with bright up.
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Old 06-28-2011, 09:09 AM
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ok I thought it working fine before a cap change.

the doubler cap is the one with a cardboard cover, its neg is NOT connected to the chassis, therefore ist possilble it could be installed backwards.

Back to the problem, sounds like HV issue. I would do some voltage checks of the B+ per the sams directions. then check both the HOT cathode and shunt cathode as previously described.

You could also try disconnecting the shunt plate to see if the HV comes up to 30kv or so if it does then its prob the shunt.
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Old 06-28-2011, 09:45 AM
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that cap was one of the first ones i did and all was ok so its not that one.the hv pot dont measure 500k , it shows .512 mohm and 300k ohm in the middle and 61 ohm full clock so thats not right and i took it apart and the resistor it self mostly all the way around is shiny which to me it had got hot it seems.
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Old 06-28-2011, 01:52 PM
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well the hv pot is good but i did find a possible mistake in the sams or the cap c3 which shows 50v 250uf but the cap shows 50v 50 uf and 250v 100uf but cap shows 250v 20uf this is not good even though the cap says what it says i put what the cap had on it but this set seems to be lacking power somewhere and i am not finding anything wrong and the only thing that is different is these 2 caps. im thinking the cap was marked wrong so im going to put in what the sams says. one of these caps go to 2 heavy resistors and a low uf cap just dont seem right these values are way off and again this all started after changing these caps and only diff is the 2 here. anyone ever run across something like a cap marked wrong like this? did this happen in old electronics of the 60s or earlier?
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