Zenith Rectangular Color... - Page 2 - Videokarma.org TV - Video

zenith2134 · #16 03-17-2009, 05:00 PM

The library doesn't have any Sams anymore

What gives?

I spent about a half hour reflowing joints in the chassis and tried just about everything I know, to no avail. It's a shame since the set works 100 percent perfectly except no luma.

Unfortunately, I may have to unload the set, since my knowledge of tubed-chassis TV's ends here.

*zenithfan1* · #17 03-17-2009, 05:02 PM

The last ALL American Zenith was in 1968, after that the outsourcing slowly began with small parts like the purity ring assemblies and so on. This however, is a very reliable set worth fixing. Even with the foreign parts the Zenith sets were good to about 1980 IMO. Post some pics Tom!!!!

*zenithfan1* · #18 03-17-2009, 05:04 PM

Quote:

Originally Posted by zenith2134

The library doesn't have any Sams anymore

What gives?

I spent about a half hour reflowing joints in the chassis and tried just about everything I know, to no avail. It's a shame since the set works 100 percent perfectly except no luma.

Unfortunately, I may have to unload the set, since my knowledge of tubed-chassis TV's ends here.

Man, where's Doug been?? These are his specialty. Don't give up yet, it's most likely something very simple as it worked fine before. Come back and give it another try in a day or so. Frustration will hide a problem that's in your face with a blinking light and sign.

*zenithfan1* · #19 03-17-2009, 05:07 PM

Tom, is there a way you can check those transistors? What part of the set are they in? video? IF? Luma? One may be bad. I was told this a while back but don't remember all the details.

zenith2134 · #20 03-17-2009, 05:09 PM

Hey Mark thanks for the response.

I can't post any pics here anymore, since I'm on probation for a minor offense...Hopefully the moderators will let me gain back this privilege soon...

For good measure I pulled all the pin-type wire connections and scrubbed up down with high grade isopropyl. And from what I saw briefly, this set does make quite a good pic. If I get it running again it'll be my daily watcher.

zenith2134 · #21 03-17-2009, 05:10 PM

Yes I did check the transistors they appear to be used in the color amp circuit and maybe the IF.

*zenithfan1* · #22 03-17-2009, 05:14 PM

Hmmmm.....I'll keep thinking about it, maybe I'll remember something useful...

Just don't give up yet!! Sets seem to be hiding in '09.

zenith2134 · #23 03-17-2009, 05:16 PM

I was surprised to find this one. Haven't found a set this old on the curb in more than 2 years.

Just quick update, which might mean nothing. There are 2 Belfuses in the set right near the power Tx. One orange, one green. When I pull the green one the raster goes totally white with retrace. No idea what this means....

radiotvnut · #24 03-17-2009, 05:30 PM

Quote:

Originally Posted by zenithfan1

Man, where's Doug been?? These are his specialty. Don't give up yet, it's most likely something very simple as it worked fine before. Come back and give it another try in a day or so. Frustration will hide a problem that's in your face with a blinking light and sign.

Yes, where has he been? I hope he's OK!

drh4683 · #25 03-17-2009, 08:41 PM

Hello all, Im still here! I havn't been here in a while.

Tom, glad you were able to save this TV. the 25CC50 is the last "tube" chassis before it was dropped and zenith just kept making the 4 tube hybrids for a couple more years.
I assume you can get a bright set up line with the switch in setup mode?
You mentioned that you checked the transistors, but I know it was discussed that you tried moving them in their sockets. Just want to be sure if you actually tested them? There are 7 easy accessable transistors like you mentioned. Those video amp transistors are suspect. Even the verticle blanker transistor can cause a dark raster if its faulty.
FYI, there are 3 more transistors in there, which are under that white plastic retainter clip. Those are the Video outputs, which have heatsinks around them. Doubt those are the issue though. If one of those fails, then you just loose the corresponding color.

This really sounds like transistor fault here. If you can't test them, try a zap of freeze spray on those transistors, one a time to see if it brings the raster back.

*zenithfan1* · #26 03-17-2009, 08:52 PM

Glad to see you around Doug! Thanks for helping Tom! Also, thanks for jogging my memory, I remember you telling me about those transistors, but that was a while ago.

zenith2134 · #27 03-17-2009, 09:01 PM

Okay here it goes. I pulled the tube compliment chart out of the set for reference.

121-447 : Noise amp
121-745 x2 : 1st Video Amp and Brightness Limiter
121-744 : 2nd Video
121-499 : AGC
121-587 : Blanker
121-746 : 3rd Video

Now, the 3 video outputs transistors are labeled 121-828 on the chart but are actually 121-743's.

Even though I tested em all earlier, I sprayed em all just now one at a time and it didn't clear up the issue. I don't know, one moment it was plenty bright then suddenly went out. I still think it's a bad connection somewhere.

drh4683 · #28 03-17-2009, 09:13 PM

I know those solder cones can be trouble, where they are used as ground connections at the ends of the strip. Lots of times they can have a hairline crack where its soldered to the metal lug on the chassis. They can be a real troublemaker. In fact, one of the guys I know who sold zeniths new back in the 60's+70's told me that lots of times they'd have to resolder those ground lugs as they would crack in shipping, or they'd get customer complaints of strange symptoms. Only to find out it was a cracked solder cone connection. Can you try pressing down on the chassis in various parts with the set on, if you have an intermittent condition, the flexing of the chassis might help you pinpoint where the trouble is.

zenith2134 · #29 03-17-2009, 09:18 PM

Doug, thanks for your assistance. While I didn't reflow all of those cone type connections, I did most of it. And I tried flexing/lightly banging on various parts of the chassis. Weird problems like this are the worst.

zenith2134 · #30 03-17-2009, 09:26 PM

Couple of other things to note...

To answer your question from before, Doug- In service mode all is okay and I can get a perfect white line. I also cleaned out the service switch of course.

When tuning in a channel, the snow is as bright as can be, and as soon as it locks into a channel it goes contrasty and color stays normal but luma disappears. This made me think that the tuner was at fault but it seems fine and I subbed the two tubes just in case.

Also, what does the white screen w/ retrace mean when i pull the 350mA belfuse? Getting frustrated lol.