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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Sep Thu 28, 2017 4:02 am 
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Joined: Jun Thu 29, 2017 2:00 am
Posts: 19
Location: Seattle
PROGRESS MADE! (Sort of)

So I put in the new HV tripler courtesy of Findm-Keepm. Switched it on, and some LOUD arcing happened (I even saw a bit of flashing light pop out the back). But, it stopped after about half a second, as if it was sputtering to life. I then saw raster (so the tube is good) but there was no static, just a white screen (settings were actually out of wack, so it looked more like a lime green screen). So what now? Is it safe to turn it on again? What should I look for now?


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Sep Thu 28, 2017 2:55 pm 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 308
Location: New Hampshire
Find the arc !
Measure the HV, should be abt 30KV
Assuming tripler is good clean the anode area the connector.
Can arc from dust inside CRT but thats usually a few quick snaps &
it burns off.
CRT sockets arc at the focus pin but thats a low hiss & smell.
For white pix clean service switch & be sure the modules are well
seated. Then take it from there.

73 Zeno 8)
LFOD !


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Sep Thu 28, 2017 3:50 pm 
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Location: Seattle
Well, I will try to test it the HV, but I would assume that the arcing was from dust, like you said (the thing has so much black soot and dust in it that when I was done replacing the tripler my hands looked like they worked on a car). Plus, the arcing didn't last long before a "picture" came in.


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Sep Thu 28, 2017 4:18 pm 
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Location: Pewaukee, WI
Some sets tend to have a bit of snap-crackle-pop on power up. If the arc sounds steady-ish or excessively loud it needs to be addressed. when a set is that dirty I typically clean the non-aquadag coated glass around the HV connection with windex and rubbing alcohol. IIRC you said this was a restaurant set...Those tend to get terribly dirty with all matter of conductive dust and grease.

First power ups of CCII sets after repairs I tend to keep the back open, stand in back with a mirror reflecting the screen so I can see any problems inside the set while watching for a pix on screen.


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Sep Thu 28, 2017 4:47 pm 
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Yeah, it was from a pub. I assume they stopped using it when they got an upgrade and they brought it out front porch in the rain when they moved.I'll give it a good clean, and see if I can get any signal.


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Sep Fri 29, 2017 12:55 am 
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Joined: Jun Thu 29, 2017 2:00 am
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Location: Seattle
I made a video of what it's doing right now:
https://youtu.be/EtEzK4c55Ro

I'm sending a video signal with my super nintendo, and it was getting a picture of the game, but it was VERY messed up. The colors seemed okay, but the screen was shaking and green horizontal bars were everywhere. It did this green screen thing in the video once before, but it flickered back to the signal. It would only do the green screen after I turned on test mode, and I turned on test mode again and it didn't recover. I'm also hearing some consistent but quiet crackling from the high voltage area, and it seems to get worse the longer I keep it on. It also seems to be affecting the screen slightly. Once or twice I had it hissed at me for half a second and the picture got all stripey


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Sep Fri 29, 2017 1:27 pm 
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Location: New Hampshire
For green check the green G-2 control. They often got bad spots.
63-10137 IIRC you can use any of the 3 colors to replace it
or one from a hybrid or upright chassis.
BUT find the arc next before it causes trouble. Fire up set with the
lights off or use a paper towel tube to localize it. Being as dirty as
it is cleaning the anode is a must do !

73 Zeno 8)
LFOD !


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Sep Sat 30, 2017 12:58 am 
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I so I turn the TV on with a sheet over my window to look for the steady quiet arc, and instead I heard one loud arc. However, the TV is still doing the green screen as before, and the steady arc has stopped. Definitely looks like a sign that it needs to be cleaned more. Also, I changed the G-2 settings and managed to get a white screen, so it appears to not be getting any signal from the tuner, not even static. Also, the colors are misaligned in the top left corner of the screen. While typing this the TV cracked one loud arc again just like when I turned it on, so had to turn it off. When I turn the TV off it consistently will briefly show a trinity pattern of all the phosphors in tbe center of the screen before fading away. Is that normal?


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Oct Mon 02, 2017 3:11 pm 
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Location: Pewaukee, WI
Power off patterns differ from set to set. If the spots are not significantly brighter than normal screen white level over the same area as the spot, and it does not stay lit for more than ~10 seconds then there is no harm in it.

BTW you may want to go trough and check all your power supply B+/B- voltages, the under-scan in your video on both axes makes me think one or more supplies may be bad. If one such supply is weak and used by the RF/IF/Video stages that could be most of the no signal problem.

The corner issue is probably the set needing a degauss/Purity and or convergence adjustment...Both of those are best done with a test pattern, and after the height width and linearity are confirmed to be set correctly, so fix the under-scan, and get video on it before worrying about that.

If all the Tuner/IF/RF voltages are correct you may want to clean the tuner contacts. Having a tool that can generate IF, and video signals such as a B&K 1075/1076/1077 series analyst or sencor VA-62 can be a useful time saver in troubleshooting no signal issues. On TVs mid-50's or later the sound is taken off at the last stage of video IF so if you can get sound through it, but not picture it narrows down the problem substantially.


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Oct Mon 02, 2017 6:59 pm 
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Joined: Sep Tue 30, 2014 6:08 am
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Location: The Old Dominion VA 23518
Is there a normal-service switch on these sets? If so, make sure it's set to Normal. Also, if you have the Sams photofact, a check of all the power supply sources might be a good starting point. Look for any DC voltage that is low, pulsing, or dancing around (unregulated). IIRC, the +24V supply in these sets was the most critical, going to just about every module.

And if it's dirty, a good reseat of the molex connectors and any modules wouldn't hurt.

_________________
Brian
"Capacitor Cosmetologist since 1979"
USN Retired 1984-2006 (Avionics/Cal)


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Oct Tue 10, 2017 1:03 am 
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Location: Seattle
I took all the modules out and cleaned them up with a cotton swab and IPA, and air dusted the whole thing. Still, all I'm getting is a white raster. I don't have the Sam's photofact so I just have to skip the voltage testing. I noticed that the little slide switch inside the chassis under the tube doesn't do anything. It looks to be labeled "raster" and "blank"


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Oct Tue 10, 2017 2:59 am 
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Joined: Sep Tue 30, 2014 6:08 am
Posts: 2124
Location: The Old Dominion VA 23518
Jack, I don't have the Sams either - just checked. But over on American Radio History, PF Reporter magazine has a few SymCures related:
Attachment:
25EC58.gif
25EC58.gif [ 75.51 KiB | Viewed 779 times ]

_________________
Brian
"Capacitor Cosmetologist since 1979"
USN Retired 1984-2006 (Avionics/Cal)


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Nov Mon 27, 2017 5:31 pm 
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Location: Pewaukee, WI
I've got the Zenith issued schematic with voltages. Let me know if you would like a copy.


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Nov Wed 29, 2017 7:34 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 29
Just remember, you MUST use the correct type of cap when replacing. They work very hard, these caps, heavy current flow. You need a physically large cap, metallised foil caps (e.g. MKT) will NOT cut it. Trust me!

You shouldn't really call these "safety" caps. Doing so might cause someone to use mains safety caps. These are designed to fail open circuit, NOT what you want here.....

Back in the day, in my experience in Australia, the hor output transistor would get taken out before the fireworks started, when one of these caps failed O/C.

Replace them as a matter of course.


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Nov Wed 29, 2017 2:02 pm 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 308
Location: New Hampshire
All good advice !
Safety or "S" caps was a term used in the olden days by some makers. Its related to a
government mandate ( HHS IIRC ) as to X-rays. The system had to be approved by them.
Normally an open cap will blow the HOT instantly but these used 5 caps. Add to that the
HOT was quite robust so the set would run until the tripler, focus divider or CRT socket
failed. When 4 or 5 opened these sets would throw some lightning bolts & scare the
crap out of you. The HV would be around 50 KV.........

73 Zeno 8)
LFOD !



irob2345 wrote:
Just remember, you MUST use the correct type of cap when replacing. They work very hard, these caps, heavy current flow. You need a physically large cap, metallised foil caps (e.g. MKT) will NOT cut it. Trust me!

You shouldn't really call these "safety" caps. Doing so might cause someone to use mains safety caps. These are designed to fail open circuit, NOT what you want here.....

Back in the day, in my experience in Australia, the hor output transistor would get taken out before the fireworks started, when one of these caps failed O/C.

Replace them as a matter of course.


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 Post subject: Re: Zenith Chromacolor II (chassis 25EC58) going wacko
PostPosted: Nov Wed 29, 2017 2:25 pm 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 308
Location: New Hampshire
First thing is ignore the other video problems & find the arc & test the
HV !!! You can crudely test HV at the 200V supply in the symcure. If its high
the HV is high. See if the hissing is coming from the CRT socket focus pin.
A common fail on these.

Odds are the video is either the tuner or IF module. Probably caused by the arcing.
If when you change channels you see & hear the crashing of the contacts its prob
the tuner ( 175-#### ). If its dead prob the IF module ( 150-### ). Check
voltages 1st to be sure !

BTW did you inject video or put it through the tuner ???

73 Zeno 8)
LFOD !


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