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Well I'm 3/4 through recapping. I went through the electrolytics, horizontal section, vertical, part of the sync, and the audio caps. I finally have a full raster. The old cap was shorted on the cathode bypass on the vertical output.
On the second powerup I failed to ramp up the variac and a resistor smoked in the audio. The time delay relay is open and I have the B+ bridged until I have a replacement relay from Tim. I think the resistor that smoked was already on its was out as there looked like it was taking a carbon track journey! It was R53(Sams photofact) I check its resistance and it was only about 40 ohms. Clearly it was shorting out with the carbon track.
I also noticed I lacked voltage on the plate of the video output and discovered L26 peaking coil was open. On taking it out one of the leads simply detached from the body. I had continuity in the coil so I had to work at resetting the lead into the body and getting the coil to stick to the lead. It is hair thin..... I got it working and now have plate voltage on the video output tube.
Now my biggest issue is with excessive voltage on a few tubes.... After troubleshooting to get good focus, the focus pot is near 0 ohms to get good focus. Mind you its a 1k pot! That puts the plate voltage on V9 and V10(and I'm sure other tubes on that B+ line) 60 volts HIGH!!! The picture tube brightness is at full and unable to dim since that B+ line supplies the cathode of the CRT.
I know that getting good focus is dependent on load through the B+ since the focus coil is in series with the B+. I have to think that something isn't drawing enough current to load the coil(and to lower my crazy high B+)So instead of going down the troubleshooting of that I will finish recapping the rest of the set. I don't assume that replacing the remaining caps will bring down the voltage and increase the current... won't leaky paper caps tend to bring down voltage instead of causing it to be 60V high?
I'll get back to recapping Wednesday and then troubleshoot whatever else shows up.. I am happy that some things are working. Its tough trying to tell my wife that certain things are working on the set but then she asks is the tv "working".... Noooot really... Saying that I have a raster and noise through the speaker doesn't cut it as a working set. I am happy that some of the important items are working though.
The CRT appears to be a dumont original straight gun with a very noticeable ion burn in the center of the screen. This set must have been old enough where the bent gun and ion trap magnet weren't introduced yet.. Eventually I'll look at another tube that requires an ion trap. There are a couple 12 inch roundies on ebay. Got to get the TV in good running order before gambling on a good CRT.
Sorry for the length of my story of the Dumont.. Its a lot to take in and wrap my head around. I love the challenge though, as long as critical parts keep working.
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Matt Davala
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