Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Rectangular Screen Tube Televisions

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 09-21-2017, 10:25 PM
TUD1's Avatar
TUD1 TUD1 is offline
TheUniversalDave1
 
Join Date: Jan 2014
Location: Birmingham, AL
Posts: 1,430
My new Zenith 20YIC50

Got this set this weekend along with the CTC-15, but just now got around to putting it back together. The picture tube is marginal, but it will make a decent picture. The high voltage however, is out of control. When I measured it, it was at 41 KV! I tried adjusting it, but the stupid control would not move. It's the kind that you have to stick a pencil eraser or something in to adjust. I don't like it a bit. I'm just going to keep the brightness cranked, so hopefully it will keep the HV down around 30 KV, and it won't destroy the tube. I think this set uses those darn varistors, so that's probably what's wrong with it.
Attached Images
File Type: jpg IMG_1621.jpg (77.9 KB, 67 views)
File Type: jpg IMG_1619.jpg (58.1 KB, 42 views)
File Type: jpg IMG_1618.jpg (98.3 KB, 34 views)
__________________
"If people only knew how much I secretly hated them, they'd love me for holding it in." -Matt Groening
Reply With Quote
  #2  
Old 09-21-2017, 11:40 PM
MadMan's Avatar
MadMan MadMan is offline
'A Disgusting Brony'
 
Join Date: Oct 2016
Location: Chicago
Posts: 354
Decent looking set.
Reply With Quote
  #3  
Old 09-21-2017, 11:54 PM
Jon A.'s Avatar
Jon A. Jon A. is offline
Bullies beware.
 
Join Date: Jun 2013
Location: Canada
Posts: 3,962
...

Last edited by Jon A.; 09-22-2017 at 04:39 PM.
Reply With Quote
  #4  
Old 09-22-2017, 12:14 AM
TUD1's Avatar
TUD1 TUD1 is offline
TheUniversalDave1
 
Join Date: Jan 2014
Location: Birmingham, AL
Posts: 1,430
I was able to adjust the control and get the HV down to about 35 KV with a dark screen.
__________________
"If people only knew how much I secretly hated them, they'd love me for holding it in." -Matt Groening
Reply With Quote
  #5  
Old 09-22-2017, 12:34 AM
maxhifi's Avatar
maxhifi maxhifi is offline
VideoKarma Member
 
Join Date: Dec 2010
Posts: 1,337
Those color bars look great. Are you absolutely sure your high voltage probe is accurate? I know mine always reads low.
Reply With Quote
Audiokarma
  #6  
Old 09-22-2017, 12:35 AM
mrjukebox160 mrjukebox160 is offline
VideoKarma Member
 
Join Date: Aug 2016
Posts: 42
Still very high. Could be the 6HV5.
Reply With Quote
  #7  
Old 09-22-2017, 12:37 AM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 1,848
You sure that HV probe is calibrated right? 40KV is awful high for a tube type HV supply. No-load, unregulated shouldn't go much over 32-33 KV if that.

Last edited by old_coot88; 09-22-2017 at 12:40 AM.
Reply With Quote
  #8  
Old 09-22-2017, 12:42 AM
Jon A.'s Avatar
Jon A. Jon A. is offline
Bullies beware.
 
Join Date: Jun 2013
Location: Canada
Posts: 3,962
...

Last edited by Jon A.; 09-22-2017 at 04:39 PM.
Reply With Quote
  #9  
Old 09-22-2017, 02:11 AM
TUD1's Avatar
TUD1 TUD1 is offline
TheUniversalDave1
 
Join Date: Jan 2014
Location: Birmingham, AL
Posts: 1,430
I toggle between saying "twenty-why-one-see-fifty" and "twenty-why-eye-see-fifty." Saying the latter is quick and easy. This is the 21st century after all. Quick and easy is king nowadays.

I'll get the schematic out later and see if we can find that stupid varistor.
Attached Images
File Type: jpg IMG_1626.jpg (48.0 KB, 28 views)
File Type: jpg IMG_1625.jpg (90.1 KB, 37 views)
__________________
"If people only knew how much I secretly hated them, they'd love me for holding it in." -Matt Groening

Last edited by TUD1; 09-22-2017 at 02:26 AM.
Reply With Quote
  #10  
Old 09-22-2017, 02:29 AM
Jon A.'s Avatar
Jon A. Jon A. is offline
Bullies beware.
 
Join Date: Jun 2013
Location: Canada
Posts: 3,962
...

Last edited by Jon A.; 09-22-2017 at 04:39 PM.
Reply With Quote
Audiokarma
  #11  
Old 09-22-2017, 08:43 AM
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 2,782
Doug did testing & found a modern sub for the thermistor. It here
somewheres. Trouble has been the OEM's are going bad in the
package.

Keep in mind always check the tube chart for the right damper / regulator
tubes & do not sub a wrong pair.

73 Zeno
LFOD !
Reply With Quote
  #12  
Old 09-22-2017, 09:29 AM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 8,921
Here is some good reading on trouble shooting the Zenith Pulse regulator circuit:

http://videokarma.org/showpost.php?p...5&postcount=22

I believe this is doug's thread on VDR replacement.
http://videokarma.org/showthread.php...ght=Zenith+VDR
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
Reply With Quote
  #13  
Old 09-22-2017, 12:20 PM
TUD1's Avatar
TUD1 TUD1 is offline
TheUniversalDave1
 
Join Date: Jan 2014
Location: Birmingham, AL
Posts: 1,430
Doug showed me agood replacement for the varistor on the FB page.
__________________
"If people only knew how much I secretly hated them, they'd love me for holding it in." -Matt Groening
Reply With Quote
  #14  
Old 09-22-2017, 12:57 PM
TUD1's Avatar
TUD1 TUD1 is offline
TheUniversalDave1
 
Join Date: Jan 2014
Location: Birmingham, AL
Posts: 1,430
Here's the offending part on the schematic.
Attached Images
File Type: jpg IMG_1629.jpg (64.4 KB, 33 views)
__________________
"If people only knew how much I secretly hated them, they'd love me for holding it in." -Matt Groening
Reply With Quote
  #15  
Old 09-22-2017, 02:06 PM
Findm-Keepm's Avatar
Findm-Keepm Findm-Keepm is offline
Followin' the Rules...
 
Join Date: Jun 2007
Posts: 2,835
Save your old Varistor if possible - I'd like to have it, to investigate the failure curve.

When Doug did his experiment(s), I took to my own Zenith Varistor stash to see if I had any that had failed. Of 9 unused/NOS, all 9 were good. Of 7 pulls from various chassis, and some identified only by comparing the body color markings to NOS ones, I was able to see only one failure - a beige/purple striped Varistor that was open - no response all the way to 1KV.

Silicon Carbide Varistors (what Zenith and other TVs used) have a different V/I curve than the semiconductor MOVs Doug used. The SiC varistors all have a linear V/I curve, and like MOVs, they are rated by "some voltage at some current" with the most prevalent current being 1mA. So if a SiC varistor is rated at 400V @1mA, applying 400V DC to the varistor in a closed circuit will yield 1mA of current flowing. Some Zenith varistors are rated to 950V, not a problem for me to measure with a Fluke 332D 0-1000VDC (okay, only 999.999V) voltage standard with a current compliance to 20mA, plenty of room for varistor testing.

About 4 years ago, I got a Zenith 800-600 Zenith Varistor/Thermistor kit with 90% of the varistors being new, unused. All had good V/I measurements. My workman stash got raided as well, with only one (used, solder on leads) varistor being w-a-a-y out, topping at 560V for a 410V varistor.

If you wanna try an original, lemme know what you have, and I'll send you a NOS one, free, if I have one - and verified good.
__________________
Brian
USN RET (Avionics / Cal)
CET- Consumer Repair and Avionics ('88)
"Capacitor Cosmetologist since '79"

When fuses go to work, they quit!
Reply With Quote
Audiokarma
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 10:16 PM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
ęCopyright 2012 VideoKarma.org, All rights reserved.