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  #1  
Old 10-21-2007, 09:36 PM
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zenith roundie-help!

just got stated on my zenith 25lc20 chassis roundie. did a slow start and this set came up and played. tube doesnt too good though. plenty bright and the contrast is there-focus at max,maybe a rectifier.vertical is off and i can t find any controls! anyone help me? possibly buried in the chassis somewhere? thanks!
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Old 10-21-2007, 09:48 PM
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Those controls gave me fits too.

One is behind an un-labeled hole in the control area.

The other is concentric with another control (Vert?) if I recall correctly.
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Old 10-21-2007, 09:50 PM
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Here is the post of mine...

http://www.audiokarma.org/forums/sho...ghlight=toledo
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Old 10-22-2007, 07:15 AM
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Vertical Setup Controls

The height control is concentric with the brightness control. I have the 25MC33 chassis, yours should be similar. The brightness knob should have a small hole in the center (if it's on the correct shaft). Insert a thin flat blade screwdriver and adjust. The linearity control is in an unmarked hole in the control panel as posted earlier. They are a little tricky to locate but the Zenith engineers were thoughtful enough to put these controls in front where the settings can be observed much more easily. You can touch up the vertical as needed without ever moving the set. I hope this helps and enjoy that roundie. There is nothing like a Zenith.
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Old 10-22-2007, 03:55 PM
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thanks for help! yes ,i found them. one in the brightness shaft and the other in un-marked hole. didn t fix problem though. i think the 6he5 is weak. proportionate,just not enough. what was there looked great! then the crt slowly faded. i guess i will just have to get out the b&k. i have nothing to lose at this point. you are right-that hour of zenith roundie was wonderful!!!!
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Old 10-29-2007, 12:18 AM
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Zenith Roundie Vertical problem

HI:

Have you checked the B+ voltages? Lack of height in a Zenith could be the 160 uf electro cap in the voltage doubler B+ circuit. The 25MC chassis I worked on years ago had this problem. The 6HE5 could also be an issue. Good Luck!
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Old 10-29-2007, 01:54 PM
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I don't know what it is about tube sets but the vertical circuit seems to be the most troublesome. Maintaining sufficient vertical height on a tube set seems to require all components to be within factory tolerance. If the vertical output tube is the slightest bit weak, you will have insufficient height. Years ago, it was not uncommon to see sets in daily use with reduced vertical height that one would simply live with until it failed.
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Old 10-29-2007, 08:10 PM
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cap in the b+-that did it! we overlooked that from the beginning. replaced and i have too much vertical! (adjustment took care of it)now i just need a good crt.thanks to all who helped. i owe you guys BIGTIME!!!!!!
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  #9  
Old 10-31-2007, 05:07 PM
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Hey is this cap similar to the ctc-16 rca chassis? That's not a lytic axial cap is it? Mines got the same symptom but an RCA.. I posted this question in other posts as well. Congrats to that fix!
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Old 10-31-2007, 07:43 PM
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i am fighting a ctc 15 vertical problem as we speak. i can t seem to get anything
but vertical problems. i ve also got a ctc 16 (25AXP22) that had a slight vertica
and a convergence issue. turned out well. as far as your 15,that outout oscillator can do many stange things. there is a cap next to it that can leak down during operation. let me know what you find. these guys on this board are the best techs in the world!
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  #11  
Old 10-31-2007, 08:01 PM
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Quote:
Originally Posted by freakaftr8 View Post
Hey is this cap similar to the ctc-16 rca chassis? That's not a lytic axial cap is it? Mines got the same symptom but an RCA.. I posted this question in other posts as well. Congrats to that fix!
I believe they are talking about a voltage doubler cap. Most roundies, including a majority of the Zeniths, have a voltage-doubler power supply. These are nearly identical even across brands. The arrangement uses two silicon diodes and two 160mfd capacitors to acomplish the doubling. The ctc-16, however, is one of the exceptions. It does not have a voltage doubler, but uses a bridge rectifier instead.

John
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