While I was able to adjust the set to give a good picture, there was still a problem with the horizontal. I wasn't able to adjust it according to the service literature. Basically you're supposed to remove the discriminator tube, the 6AL5, adjust the frequency until the bar moves slowly across the screen and reinsert the tube. It should lock in at this point and then you adjust the phase.
They then have test the pull-in range by adjusting the frequency CCW until it unlocks, then adjust it back slowly until it locks in and you count the number of bars just before it locks in. Then CW and count the bars. They're supposed to be between 3-4 bars in both cases. In my case when I turned it one way it would just slowly drift across. In the other direction it wouldn't unlock until I made many turns.
I also wasn't able to adjust the phase independently.
I checked all the caps and resistors. I replaced the micas. Nothing helped. I started to suspect the horizontal oscillator transformer. But, I noticed that the DC level on the grid of the 6AU6 control tube was -1V when it should have been -3V. The 6AU6 is used as a reactance tube to control the frequency based on the output of the phase discriminator. -1V put it at one end of it's control range so it could only adjust the frequency in one direction if the free running frequency was set correctly.
The bias is determined by dividing down the -125V supply. First they divide it down to -30V with a low impedance divider then down to -3 with a 10meg and 1meg in series. I checked those and they were o.k. I was getting close to modifying it to give the right bias when I decided to swap the 6AU6 even though it tested as new and seemed to work. Well the bias went to -3V with the new tube and I was able to align the horizontal sweep as per the service manual. The grid on the 6AU6 was drawing 0.2 microamps at -1volt. My tube tester isn't going to notice that.
Now the only problem I have is with the FM. Although it worked great in the beginning, it is now fading out after 4 minutes. It runs for 4 minutes after turning on and then suddenly the volume drops.
I've replaced two micamold caps. One was leaky, the other was o.k. Some resistors are out of spec, but I don't think they're at fault.
What is curious is that the AM function works fine even when the FM has dropped in volume. They both use the same circuitry except different IF transformers and osc frequency. There must be a clue in this.
You can see the schematic for the radio section on the last page of:
https://www.msu.edu/~yurkon/Sylvania_9-2_Sup1.pdf
This is getting to be really frustrating. I swapped all the tubes in the radio after my experience with the horizontal 6AU6 but it didn't make a difference. Any suggestions for what to look for would be welcome.
I'd like to get it off my bench so I can work on my alignment generator and get it working. I want to touch up the alignment since I had to rewind one of the video IF transformers.
I'm also working on making a bezel for the 12" version of this set. A friend drew a mold up for me based on my measurements. I didn't notice however that the had made the face a cylinder instead of a sphere. It wasn't obvious in the preview. It became obvious when the shop I'm using tested their programming on a shape board.
If I'm able to cast a 12" bezel then I'll put a 12LP4 into the chassis. It should really be a 12VP4 but I'm unlikely to find one of those. I'll have to add a screen bias supply. One of the 16" Sylvania shows a circuit to do that, based on this power supply.
This is basically changing it from a 1-076 model to a 1-128 model. I have the cabinet from my family's 1-128, just nothing is left of the electronics. The 1-108 chassis was used in both. If I can't successfully cast a bezel I'll refinish the 1-076 cabinet and stick with it.
John