77 sylvania

[Reece]

Those sweep transistors give trouble from heat, I've used more heat sink grease between them and their sink and added more homemade aluminum fins with good results. Also crimped their leads a little like bobby pins to get more grip inside the sockets.

[DaveWM]

I have a spare board that donated the transistor from, there was also one on that board that was not orig, it was a different color body and had been bolted to the sink, rather than rely on the spring clip that held it on.

[holmesuser01]

Well, good. This one's done. Now, come on up to NC and help me get this DuMont, Magnavox, and the other Magnavox going!!!

Bruce

[DaveWM]

would love to, but got a few more still to go.

[DaveWM]

the vert nonsence reared its ugly head again, slight fold over on the bottom and shaking pic. Pulled the board, both output transistors checked ok, so I replaced the 2500uf coupling cap from the collector of the output transistor to the yoke. I only had a 1500uf handing so I ran down to the shack and got a 1000uf. the 1500 went in from the top, the 1000uf was attached to the bottom (using the wires from the top cap as stakes to pig tail too). Seems to have resolved it, will watch Jimmy and Angle later and see how it hold up.

I should have replace that cap orig, I figure its got to see lots of hard use.

[bgadow]

I have a mid-70s Sylvania that also suffers from some vertical jitter. I'll remember this thread the next time I dig into it. One thing I found, and it might be worth checking if you haven't already: the service switch is sorta cheap and not well mounted to the board. It is real easy, when installing the back, to not have the button lined up with the hole. On mine a couple of the posts had been pulled loose from the board due to this, and the intermittent contact was causing both a video and vertical problem. As I write this, I recall that it was mostly video (raster would go dark/negative) but worth checking if you are in there already.

[DaveWM]

the cap did the trick, rock solid. My cap tester only goes to 1000uf so I could only test it for leakage. I figure it may have been an ESR issue rather than a leakage issue. I had noticed before the jitters started to happen that the pic was shrinking up from the bottom a bit more than normal. At 1st I attributed it to just the way a thermistor in a yoke may have been behaving, but now I think it may have been the cap. I know ESR goes down with heat, and the cap sits right next to the heat sink from the defection transistors. I am pretty sure I checked on that switch when I 1st started trouble shooting the vert (that was a problem from the get go).