screen issue - Videokarma.org TV - Video

radio nut · #1 07-25-2009, 03:34 PM

My next project is a CBS-Colombia tv. As of now it is up and running. I have noticed that the left half of the screen is a little brighter than the right. The horiz. hold moves that left side brightness around though. All caps are new, all not really close resistors are replaced, and the tubes are nos. The only thing I have not checked is for gassy tubes(My main tube tester broke and my other does not check for gas).I currently do not have spare tubes for this set to sub in.What would likely be the cause of this condition?

John Marinello · #2 07-25-2009, 05:23 PM

How is the linearity?

radio nut · #3 07-25-2009, 06:06 PM

The set has a very very good picture other than this.I got bored and started unsoldering caps and checking them on a cap checker/bridge. I found two that were bad. Now that I have replaced them with tested good caps, I am left with only a brighter than the rest of the screen white line about in the center of the screen. I now have a "Sam's" small magazine that people wrote in with problems and "Sam's" would discuss possible solutions. For A bright line They Said It was the horiz. output tube being overbiased. My set should run -25 volts and mine is running currently -18v. I do not have a scope to see if it could be getting to much AC in the bias.Could this be it?

marty59 · #4 07-25-2009, 06:06 PM

Also, how is the Boost voltage and the circuitry for the Damper? Could be retrace related or as mentioned an issue with horizontal linearity.

radio nut · #5 07-25-2009, 08:22 PM

The boost voltage should be 500v. and is about 458 or so. I "assume" it was low due to the -18 volt bias instead of -25 on the horiz. output tube.The vert. linearity I think is good because the picture is good, Or is this a scope/waveform question? I am checking in to buying a scope, I just do not have one now.On the damper part of your question, how do I further check it?

radio nut · #6 07-25-2009, 08:24 PM

I also did add a 100pf.3,000 volt cap in the damper circuit as mentioned by the "sam's" article on this issue.

radio nut · #7 07-26-2009, 10:01 AM

Well, I hate to say this but the new people to this hobby should use my last 2 threads as an example of what not to do. I was told by another tv person that you need to take your time on these projects. I am the kind of person that wants everything fixed yesterday.This leads to doing and not reading CAREFULLY.I have yet to calibrate my set and am currently working on getting a scope.So, what do I do, I falsely "assume" that my set is broke, when if I would just take the time to read the fine print I would not have an issue. The Horiz. sweep directions state that after adjusting the waveform slug that the drive is adjusted till you get a white line in the screen and then back off the adjustment till the line just disappears.So, this as of now is a calibration issue and not a problem.I really do not like to admit something like this on a world wide forum but this is a good lesson for those who are starting out. READ every bit of information on your set before you start. Thank you! for those who try to help me, I wil have to work on myself and my tv's at the same time!

marty59 · #8 07-26-2009, 12:24 PM

Please, don't bang your head too hard against the wall! Seriously, I thank you for acknowledging and sharing your oversight. Many times on these threads through the course of troubleshooting-analysis the solution is staring you right in the face and we're right here with you!

I won't ever claim to know everything but the miracle of this hobby (and electronics) is that you never stop learning and there's some fun and accomplishment-satisfaction along the way. Plus, if you haven't done something in a while these threads do a good service to rekindle those forgotten processes too.

Dan Starnes · #9 07-26-2009, 04:59 PM

I did the same stuff on my Philco combo. Went back to the basics and did as you did, problem solved, I was happy and learned a lesson, check the simple first.