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#1
11-30-2014, 07:38 PM
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Zenith 23XC38Z Chassis Losing Horiz. Width
Hey everyone,
My daily watcher 1967 Zenith with the 23XC38Z chassis has been slowly losing Horizontal width at both edges of the screen over the past few weeks, however, the shrink has been much more noticeable over the past couple times I've had the set on. It gets about 2-4 hours of use a day, five days a week, and Ive been in using it in this capacity since about 2011. In that time, I've replaced a few bad electrolytic caps, the focus rectifier, a horizontal output tube, and a Damper tube. Does anyone who has any familiarity with these late 60's zenith Tube Chassis sets have any pointers on where to look for problems with Horizontal Width on the 23XC series chassis? Any help would be greatly appreciated. I've been putting off pulling the chassis to install the NOS Channel Master Rebuilt 25GP22 I picked up a few months ago. It looks like this problem gives me a reason to get off my butt and finally do that. Thanks in advance. 
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#2
11-30-2014, 08:24 PM
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The first guess would be a weak H output tube of couse. There's a 'quick and dirty' way to check it without subbing the tube.
Turn the set off for about 7 seconds, and back on. Does the width take a while to fill back out to where it was, or not? If it does, it's likely the H out tube. (The '7 seconds off' test can also reveal borderline weak H osc., 3.58 color osc., Vert out, RF amp tubes, etc.) Your set probbaly uses a 6BK4 HV regulator. In later Zeniths using beam triode (6HS5, 6HV5 etc.) regulator, a gassy regulator can cause loss of width. The only test for these is to sub the tube, even though it tests 'good' on a tester. Last edited by old_coot88; 11-30-2014 at 08:32 PM.
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#3
11-30-2014, 08:34 PM
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Quote:
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#4
12-01-2014, 01:34 AM
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Quote:
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#5
12-01-2014, 06:25 AM
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Looks like all left is the damper. Also there is a VDR in
the HV reg that causes a minor width problem. On newer sets HV control gets a bad spot but also only causes minor problems most would ignore. Power supply also poss. but you should get hum bars in that case. BTW the OEM Zenith VDR's are going bad on the shelf. There is a sub for it, was talked about a few months ago. Since you will be pulling it probably best to replace it and the 2 vert integrators, all high failure stuff. 73 Zeno 
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| Audiokarma |
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#6
12-01-2014, 01:24 PM
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Your set likely has a width jumper. It should have two positions 'increase' and 'normal'. Move it to increase if it is on normal. If that don't help, and the HOT is still strong, then you have a definite problem.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#8
12-01-2014, 02:39 PM
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note this set uses a voltage doubler, so if B+ is low I would start there. Also while I doubt its a problem, there is a Thermistor in the B+ circuit, just in case you may want to check the voltage drop across it after it warms up.
If the cans are orig, see if they are warm (remember on doublers one of the cans while have voltage on the case with respect to the chassis, should have a cardboard cover). Confirm line voltage ok (I go to the easy stuff 1st). If B+ is ok then I would start checking voltage on the 6JS6 tube mainly the control grid voltage (-60v)and the screen (135v). other things, are those large white tube caps, think at least one is a boost filter cap, maybe leaky if not replaced already. .1 1kv could be loading down the fly. Last edited by DaveWM; 12-01-2014 at 03:01 PM.
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#9
12-02-2014, 08:59 PM
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Quote:
The caps on the doubler were going south. I'm going to go ahead and replace them and the last of the other electrolytics I haven't replaced yet. Thanks for the help guys!
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#10
12-03-2014, 01:34 AM
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Also, does anyone have a service manual scan for this chassis? I want to get all the cap values so I can buy the caps in one shot.
Also just an FYI but my local electronic surplus house just got a big load of NOS Thordardsen Yokes and flybacks for various tube color sets from an extinct contract service center that used to do repairs for major department stores in NE Ohio. I was able to grab two spare yokes and a spare fly for this set for $30, and I talked the owner into holding onto the rest for a while and not selling the lot for copper scrap. Just thought I'd let you guys know. http://www.electronicsurplus.com/cat...?q=+THORDARSON Last edited by fsjonsey; 12-03-2014 at 01:40 AM.
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| Audiokarma |
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#11
12-24-2014, 02:57 PM
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Sounds like the yoke....... yah, I know it's a new one.... you still got the original....?
We need a picture, several... when it's first on, and after a while... .
__________________
Yes you can call me "Squirrel boy"
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#12
12-24-2014, 03:36 PM
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its the after a while bit that makes me think its the pin cushion correction cap, if its just a 1/2 inch narrowing from top to bottom or bottom to top, then I would put money on that cap being an issue. Its even mentioned in the zenith tab manual case history as something that is often thought to be a yoke issue. Its just a lot less.
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#13
12-24-2014, 03:51 PM
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found it, knew I had messed with this before
http://www.videokarma.org/showpost.p...2&postcount=39 the full description stars on post 33
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