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  #31  
Old 12-07-2011, 10:27 PM
DaveWM DaveWM is offline
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with that briight a red raster I think your CRT is prob fine. You should go thru the setup procedure, serv switch to serv, CRT bias fully CCW, no signal to set, turn up the G2's one at a time until you just see a horz line, turn up each color until you just see each, all about the same. Return the serv switch to normal. if any one color fails to produce a line, then slowly turn up the crt bias until that line is produced with the G2 at the max, then adj the other colors down until they are all the same, just visable lines.

If you dont have enough brightness, suspect the video out tube. If its weak it causes the cathode of the CRT to be to high, thus cutting off the tube. A quick check of the CRT pins voltages will confirm this (the cathodes and the G1).

Lack of contrast is prob due to an open bypass cap (large value 50-100uf) on the video out tube cathode, follow the contrast pot lead it should connect to it, prob a section of a multisection can cap.

Lack of focus is prob a focus rectifier (tube or Se stick), but the seeming lack of focus may just be the lack of gain from the video out tube (that 50-100uf cap above). Try bridging a new cap over that and see if the contrast and focus improves. If the contrast control is doing very little then its most likely that cap.

with that much red the prob is def not the CRT.

Last edited by DaveWM; 12-07-2011 at 10:39 PM.
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  #32  
Old 12-07-2011, 10:38 PM
DaveWM DaveWM is offline
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also since you are getting a B&W pic then all the guns are working. No color, I would start with the obvious, clean the color control, clean all the tube pins and sockets with your fav contract cleaner. Wiggle the chroma tube (burst amp, osc,demodulator tubes). if still nothing you can use a scope and check for waveforms with a sams, or just get some new tubes (I would suspect the 3.58mhz osc 1st). replace the color killer tube. Some times the color crystal will be bad, you may seen barber pole colors, sometime just a purple overall color, depends on just how far out of whack the osc is running. again a scope is best also voltage checks and tube replacement of the chroma tubes.
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  #33  
Old 12-08-2011, 07:34 AM
Daave Daave is offline
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Thanks for all that info! What should the cathode and G1 Voltages be? Or is that on the schematic? Im new to this and will learn

The red raster in the picture exaggerates its brightness, but when I did a quick setup as you described above, the line is sharp and defined and well focused much better than the tuned picture is so you are probably right the problem might be somewhere else.
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  #34  
Old 12-08-2011, 08:29 AM
DaveWM DaveWM is offline
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yea if you can get a sharp bright line with the bias all the way down, then you are good on the CRT.

The voltage are on the schmatic, pins 4/13/5 around 300v (cathodes) 6/12/2 200v (G1) 11/3/9G2 around 700
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  #35  
Old 12-08-2011, 08:35 AM
Daave Daave is offline
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Awesome thanks! I did notice though that the green line dims out at the left edge, the other 2 colours didn't do that, but all 3 lines are bright with the bias all the way CCW.
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  #36  
Old 12-08-2011, 08:45 AM
DaveWM DaveWM is offline
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would not worry about that green yet.

do not compensate for dim pic with the crt bias, if its dim and the setup shows the lines then you need to look elsewhere, your set is trying to tell you something is wrong. My guess is a weak video out.

there is also a brightness range pot on some zeniths that limits the action of the user adj brightness. It is set by adj reg brightness to full then turning the range to just before the pic blooms out. there are some resistors to check as well just look aound the brighness circuit. check the voltage on the screen of the video out. this is where a scope is handy since you could look at the PP of the signals and see if it looks good.
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  #37  
Old 12-08-2011, 09:21 PM
Daave Daave is offline
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I took the measurements and compared to the schematic.

Cathodes
Pins 4-13-5 Schematic said 275, I read between 275 and 280.

G1s
Pin 6 Called for 230, I read 171
Pin 12 called for 230, I read 176
Pin 2 called for 220, I read 165


G2

Pin 7 Called for 475, I read 750v
Pin 11 Called for 425 I read 763v
Pin 3 Called for 445, I read 776v

These could all be easily adjusted to the specific voltages by adjusting the gain pots. but my picture disappeared

These were all read with the simple setup performed and a signal to the tv. I read the filament voltage and it reads on my meter at 6.09 volts, not sure if this is just a variance in my meter or the actual voltage and/or if that small amount would make any difference.

If I understand any of this, the Low G1 voltage combined with low brightness isn't a good thing., as well as the higher g2 voltage required to produce any image. Im still new, but all of that points to a weak CRT to me? Im really open to being corrected though

Last edited by Daave; 12-08-2011 at 10:11 PM.
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  #38  
Old 12-09-2011, 08:23 AM
DaveWM DaveWM is offline
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Quote:
Originally Posted by Daave View Post
I took the measurements and compared to the schematic.

Cathodes
Pins 4-13-5 Schematic said 275, I read between 275 and 280.

G1s
Pin 6 Called for 230, I read 171
Pin 12 called for 230, I read 176
Pin 2 called for 220, I read 165


G2

Pin 7 Called for 475, I read 750v
Pin 11 Called for 425 I read 763v
Pin 3 Called for 445, I read 776v

These could all be easily adjusted to the specific voltages by adjusting the gain pots. but my picture disappeared


These were all read with the simple setup performed and a signal to the tv. I read the filament voltage and it reads on my meter at 6.09 volts, not sure if this is just a variance in my meter or the actual voltage and/or if that small amount would make any difference.

If I understand any of this, the Low G1 voltage combined with low brightness isn't a good thing., as well as the higher g2 voltage required to produce any image. Im still new, but all of that points to a weak CRT to me? Im really open to being corrected though
why does that point to a weak CRT, you keep saying that. Sounds more like maybe a HV issue IF by the pic disappeared you really mean it bloomed away.

IF its blooming I would check out the HV. The pic is dark because the CRT is being cut off by the low G1 voltage and the low screens. If you can get a red raster like you had then the CRT is fine.

if you really think its the CRT you should get a CRT tester. Just dont be tempted to rejuvenate it. the LAST thing I worry about is the CRT get everything else working, even a VERY weak crt will produce a watchable pic, not great but you should be able to get everything sorted out as far as color, image, sync, etc....

oh and voltages should be checked with NO signal.
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  #39  
Old 12-09-2011, 08:42 AM
DaveWM DaveWM is offline
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checked my zenith color service man (RL goodman) shows 290/175/640 for K/g1/g2.

check your HV and focus voltages. you will need a HV prob for this.

if you have not already, you should try a new 1v2 AND 3AT2. I generally sub out all new HV tubes when HV is not right. (damper,hot,shunt,hv rec, focus rec). If that fixes it I leave the new rec tubes in, and try the old HOT and Shunt to see if the HV holds. the rec tubes are cheap so I leave the new ones in.
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  #40  
Old 12-09-2011, 09:05 AM
Daave Daave is offline
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Smile

Yea I guess Im not sure what happens when a CRT cuts off. It can produce relatively bright rasters on all 3 colours. If the tube is weak I am ok with it if I can get it to make a watchable pic. Its not going to be a daily watcher.

Im limited in my testing equipment, I don't have a HV probe or a scope, and have no issues getting something, if it will help me fix it.
Is there ways to work on checking some of the HV out without the HV probe? What are they worth? Or is it just easier to get new tubes and try that first.

I already have a new HOT, and damper. But the focus and HV rectifiers look to have been there since the set was new. The old HOT was making a blue arc internally. I do appreciate the help guys maybe Im just a pessimist.
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  #41  
Old 12-09-2011, 09:18 AM
DaveWM DaveWM is offline
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if you can get decent rasters on all colors the CRT is not weak.

replacement those tubes. HV probs are not expensive, should be able to find one on ebay for 10-15$, very handy esp for discharging the crt (some use a grounded flat blade screw driver, but if you have the prob its just easier).

if it blooms out that is prob the ones. Have you checked the current thru the HOT? if its blooming its not being cut off but rather the HV is going away, either because the CRT is drawing too much current (incorrect CRT bias pot setting or some other defect in the drive circuits) OR the HV is simply not up to the job of providing the required current at the needed voltage.

Last edited by DaveWM; 12-09-2011 at 09:21 AM.
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  #42  
Old 12-13-2011, 12:52 PM
Daave Daave is offline
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How can I power up the chassis with no CRT/yoke ?
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  #43  
Old 12-23-2011, 11:47 PM
Daave Daave is offline
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Ok I got it recapped, and that bought me the contrast control and sound back. I replaced the focus rectifier tube and that got me colour back (not sure how that works). But I tried to replace the shunt tube and the rectifier tube in the HV cage with NOS tubes and that got me very low HV and the pic kept blooming away, The shunt tube was a 6el4, and the new one was a 6el4a.(I had a few of these and none worked) So I put back the originals. But as a whole a huge improvement, watchable picture, good sound, but still won't go that bright (the first 3/4 of the brightness control is a black screen). I don't have an HV probe yet so not sure if the HV is still low? or possibly something else.

Some pics!
Attached Images
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File Type: jpg IMG_0372.jpg (44.3 KB, 22 views)
File Type: jpg IMG_0368.jpg (72.0 KB, 22 views)

Last edited by Daave; 12-23-2011 at 11:51 PM.
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  #44  
Old 12-24-2011, 08:29 AM
DaveWM DaveWM is offline
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Besides G2 settings (screen pots) and CRT bias setting, the video out tube can cause low brightness. Most of what I read on proper setup is to NOT compensate for low brightness by cranking up the bias or screens (above the normal setup procedure using the setup switch). If there is low brightness AFTER the setup procedure is complete, then some more work needs to be done, unless of course expectations are just too high.

I would hold up any further work and get the HV checked out and setup (correct hv, and shunt tube current).

IIRC the problem with a weak video out tube is the plate voltage ends up being high due to a lack of V drop, and since the CRT is directly coupled the CRT cathode voltage ends up higher than is should be, cutting off the CRT.
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  #45  
Old 12-24-2011, 09:17 AM
Daave Daave is offline
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I am working on an HV probe and yea don't plan on doing much else until I have it. I was very excited to have this picture on it, Im still a noob.

I do have another NOS video out tube I can sub in. The only setup Ive done is with the service switch on, Adjusted Pots just until I got a line on each gun, with the CRT bias all the way CCW. The focus adjustment is also all the way CCW to get a decent focus (but still could use more focusing)
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