Magnavox Color Roundie

[tvcollector]

It's something not making a connection, because it has happened one or twice before when messing with those tubes, I remember powering off, wiggling tubes and wires, and powering back on and the problem went away.. This time it's not.. I moved on to the sharpness control seeing how I already know what the problem is with the contrast... All tubes are lighting, I took the 6GH8 out from the sweep board and powered on and seems like no change.. I have to go to work so I have to look into this probably on Monday, is when I have free time..

[timmy]

Circuit board traces under the tube sockets probably the video output tube or more likely others. All my sets had broken connections on several sockets but you have to look closely for them . Best thing to do is resolder every tube socket and mark it off your list of problems.

[DaveWM]

what timmy is describing is shown on one of my videos working on a predicta. a tube socket extender with the test points is ideal for finding such issues. Agree using your eyes and a magnafiy glass is a good start.

[tvcollector]

I've seen Shangos recent predicta video where he actually zooms in real close to and it shows a break in the tube socket connection.. I've checked the 3 sockets that I pulled the tubed from before this problem occurred... I check with a mag lite, magnifying glass and poked in each hole with a small wire.. All of them are solid.. I'll go under the board where I have to remove the bottom metal plate, which I already did once, and this time I'll just reflow the tube sockets as timmy says.. The wire that goes to the sharp control was broken lose and the inner wires were touching each other.. But I don't think that's the problem.. I don't think anything like a resistor got burned out or else I would have smelled something or saw something cooking, unless a resistor burnt out without noticing any symptoms..

Should I spray WD40 and contact cleaner in the sockets pin holes?

[tvcollector]

I'm getting 125v at the 6EJ7 3rd video IF, sams says its suppose to be 180v, I pull the tube out of socket and the voltages jump up to about 180v.. I'm getting 150v at the 6GH8 second video amp which is about right... I get 51v at 6GH8 sync sep, suppose to be 85v.. I'm doing the test with the chassis out of the cabinet and the HV tube removed..

[DaveWM]

audio is after that tube so its not the problem.

inject a composite video signal at test point B

[tvcollector]

I reflowed tub sockets, no change.. I attached an alligator clip to test point B which is between L10 and the tube socket and touched a coax cable to it, and i can't get anything.. Not sure if I'm injecting the signal right.. all it does is make horizontal bars on one side of the screen..

[DaveWM]

what was the source of the composite video signal?

[tvcollector]

I tried cable TV, and I also tried my B&K pattern generator in IF mode...

[DaveWM]

you need to use the video, no an RF or IF modulated carrier wave.

[tvcollector]

So something like an RCA video output from something like a DVD player?

[DaveWM]

yes the video out may work. you should isolate it with a .1 uf cap to protect against any DC potential.

what model BK is it? a 1076 or 1077 would be ideal.

[tvcollector]

I used a B&K 1248 digital I.C. color generator

[tvcollector]

I connected the video output from a DVD/VCR player and was able to get a picture.. The colors were off and the horz and vertical are wacky, but I was able to see the menu screen of the player...

[DaveWM]

Well then its prob before that point then.

since you are getting audio, then the prob should be somewhere between the plate of the 3rd IF tube and the test point B.

Of course it could be an AGC voltage that is off, allowing audio but not video.

I would try clamping the AGC with a variable DC supply to see if that brings it back.