Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Solid State CRT Televisions

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 12-26-2015, 01:41 PM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 2,541
Weird problem with Sony KV-20FV12

I have a 15 year old Sony KV-20FV12 That's been working perfectly up to now. CRT nice and bright, just like brand new. Then it started a "cycling" act, appearing exactly as if the CRT heaters were being switched on and off regularly. The pic doesn't go all the way out, just fades to like very weak emission on all three guns. Then it comes back up to normal, gradually cycling in and out over about a half minute period. The change is not abrupt, but like a gradual 'breathing' effect.
But the CRT heater voltage does not change, holding a constant 5.2V AC

Anybody had a similar Sony problem?

Last edited by old_coot88; 12-26-2015 at 02:00 PM.
Reply With Quote
  #2  
Old 12-26-2015, 02:12 PM
zeno's Avatar
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 4,672
Sony AKB circuits will mute the pix if a bad CRT but
I will assume yours is OK. Usually the pix blinks
when cold & does it less with warm up.
It is also sensitive to the G-2 setting so turn it up a tad
& see what happens. Basicly if any gun cant draw enuf
current the jungle IC shuts off all Y & C. During blanking
each gun is fired & current measured. You can usually see
three color lines at the top if you shrink the vert a little.

The CRT should have about 125V on the cathodes with
normal pix & 200V no pix ( zero beam ), G-2 abt 500V any pix.
Dont remember what the G-1 did in these.

73 Zeno
Reply With Quote
  #3  
Old 12-26-2015, 04:30 PM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 2,541
Quote:
Originally Posted by zeno View Post
Sony AKB circuits will mute the pix if a bad CRT but
I will assume yours is OK. Usually the pix blinks
when cold & does it less with warm up.
It is also sensitive to the G-2 setting so turn it up a tad
& see what happens. Basicly if any gun cant draw enuf
current the jungle IC shuts off all Y & C. During blanking
each gun is fired & current measured. You can usually see
three color lines at the top if you shrink the vert a little.

The CRT should have about 125V on the cathodes with
normal pix & 200V no pix ( zero beam ), G-2 abt 500V any pix.
Dont remember what the G-1 did in these.

73 Zeno
There's no change in pic size or geometry, or in chroma or video content. The CRT socket readings are-

Heater 5.2 VAC constant, and no change in the orange glow of the cathodes.
All G1s 51V constant.
Cathodes constant 150V with no pic, with pic they fluctuate 130V-170V with scene content.
G2 700V constant (G2 control painted solid, can't turn it).

Seems like totally normal readings. And they do not change during the half-minute "cycle" between a normal, bright pic and the washed-out "extremely weak CRT" image.
There's no intermittency or abruptness, and no response to tapping the boards or CRT neck. Just the slow, gradual 'cycling' between the two states.

All I can figger it must somehow be the jug doing it. Prolly just junk the set.

Last edited by old_coot88; 12-26-2015 at 06:28 PM. Reason: Made correction; 700V not 1400V (read wrong scale)
Reply With Quote
  #4  
Old 12-26-2015, 05:16 PM
Findm-Keepm's Avatar
Findm-Keepm Findm-Keepm is offline
Followin' the Rules...
 
Join Date: Jun 2007
Posts: 2,832
Solder connections okay?

Solder connections at the CRT socket were bad on my daily watcher 20" Sony. My daughter thought I was messing with the remote - to prove her wrong, she did the soldering....

The solder connections on the CRT board were quite solder starved.
__________________
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
  #5  
Old 12-26-2015, 05:28 PM
jr_tech's Avatar
jr_tech jr_tech is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 4,510
Something has got to be changing... corroded CRT pins, perhaps ???

jr

Last edited by jr_tech; 12-26-2015 at 05:31 PM.
Reply With Quote
Audiokarma
  #6  
Old 12-26-2015, 05:32 PM
Eric H's Avatar
Eric H Eric H is offline
Administrator
 
Join Date: Jun 2002
Location: So. Calif
Posts: 11,565
I would resolder the CRT socket on the board.
It could be losing some heater voltage even if you can't see them dimming, this was a fairly common problem, it happened to a Sony monitor I had.
Reply With Quote
  #7  
Old 12-27-2015, 10:05 AM
zeno's Avatar
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 4,672
The G-2 sounds too high. It will break loose.
May be the pix is still there cause the G-2 is high
& it is actually blacking out but you cant
see it.
If thats the case you may have a weak CRT.
If so there is a trick you can try.

73 Zeno
Reply With Quote
  #8  
Old 12-27-2015, 10:53 AM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 2,541
I was reading the wrong scale (senior moment) It's 700V on G2.
Anyhow I reflowed all the pins as suggested, and cleaned the CRT pins, and no go.
It's now in the fault state permanently, the typical look of a very weak CRT.
What had me buffaloed was the slow 'cycling' between the fault state and a nice bright 'brand new' pic. It's gotta be the jug. Still dunno how or why it was doing that.
Oh well, 15 years was a pretty fair life for the set.
Thanks for the feedback.
Reply With Quote
  #9  
Old 12-27-2015, 02:09 PM
Dude111 Dude111 is offline
Analogue is Awesome
 
Join Date: Oct 2009
Posts: 2,406
Is there anyone in your area that could look @ that set for you buddy?

I feel terrible for you,dont want you to lose her.....
Reply With Quote
  #10  
Old 12-27-2015, 03:02 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
Quote:
Originally Posted by Dude111 View Post
Is there anyone in your area that could look @ that set for you buddy?

I feel terrible for you,dont want you to lose her.....
Dude...It's just a 15 year old BPC!...I can go out any day of the week and get 10 working ones just like it for free....Hell when I see a BPC on the curb I don't even test it (if I even stop), but instead just rip out everything except the cabinet and CRT to use as parts for mid 70's and older sets that actually have some value.
__________________
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
Reply With Quote
Audiokarma
  #11  
Old 12-27-2015, 04:53 PM
zeno's Avatar
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 4,672
No need to quit yet. Lets do some free stuff first.

Use a pattern no a changing source. Color bars etc.

Measure the 200 V source. To find it find 3 resistors that
go from the collectors of the 3 color outs. Typically they
are 18 K 2W +- where they join is the 200V.

Turn down the color, brite & contrast all the way.
Turn down the G-2 until you see NOTHING. The paint
will crack when you turn it hard.

Measure the collectors again. If the AKB is killing the
pix they will be 200V.

Trick for all Sonys with AKB for all listening.
Put in video mode no source.
Ground one end of a 15-18K resistor.
One at a time put the other end on each color out transistor
collector..
This makes a voltage divider that will turn that gun on heavy.
A good CRT will show just that color BRITE & usually with
retrace lines. A bad gun will give a dim & mucky pix.
Reds will look brown etc.

Trick 2 last resort.
since Sony CRT's wont rejuve find the low ohms resistor
in series with the filament & short it. Works on most
brands with low E. Risk is an open filament or H-K short but
whats to loose at that point ? We did quite a few & got a year
or two out of many sets.

73 Zeno
Reply With Quote
  #12  
Old 12-27-2015, 07:41 PM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 2,541
Thanks Zeno. But I'd already closed the thing up ready for the scrapper. I really have no interest or incentive to repair "new" stuff if the problem isn't obvious and quickly fixable.
Intransigent fuddyduddy-ism.
Reply With Quote
  #13  
Old 12-28-2015, 07:46 AM
kf4rca kf4rca is offline
VideoKarma Member
 
Join Date: Feb 2015
Location: Atlanta
Posts: 737
I've seen that before.

I rejuvenated the tube and it quit cycling.
__________________
Reply With Quote
  #14  
Old 12-28-2015, 10:10 AM
Dude111 Dude111 is offline
Analogue is Awesome
 
Join Date: Oct 2009
Posts: 2,406
Quote:
Originally Posted by Electronic M
Dude...It's just a 15 year old BPC
I hear ya buddy....
Reply With Quote
  #15  
Old 02-04-2016, 11:19 AM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 2,541
Just a little update regarding this critter. I had it all buttoned up ready for the scrapper, and then got to thinking what the heck, just use it like it is for a while. So I ran it with that horrible grey scale, near-zero emission, crappy crappy picture for several days. Danged if it didn't start "coming back to life" on its own over a period of several more days. I never touched the drives or G2 at all. Never adjusted anything. It came back to displaying a fully 'new set' picture just like it always had. And it's been holding that way ever since. Never seen 'nuthin' like it before. Don't know how long it will last, though.
Screen shot attached.
Attached Images
File Type: jpeg image.jpeg (132.4 KB, 51 views)

Last edited by old_coot88; 02-04-2016 at 11:22 AM. Reason: TYPO
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 08:29 AM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.