What could cause this?

[Findm-Keepm]

Originally Posted by SpaceAge

I opened it up today to take a look, and a few things stand out. Several large caps seem to be held in place by blobs of white silicone. Someone must have used the silicone to hold the caps in place, and then turned the board upside down and soldered the bottom. I doubt this is original, since the silicone blobs at least partially cover neighboring resistors. No way do I believe it was like that when new. Also to note is the label on the tuner is printed "NOV 09", I assume that's a date code. So apparently this thing has been worked on relatively recently.

Sony famously used silicone to fasten large items to the board - vibrations in shipping would work the part loose otherwise. After the late 80s/early 90s IF solder fiasco/money maker (out of warranty work), Sony never took another chance, and passed the bad solder problems on to JVC and their vertical chips. The RTV on some large screen CRT sets did come back to haunt Sony.

That tuner is original - The tuner's final inspection fell on 11/9 of whatever year. I have some NOS OEM tuners with Oct 23 on them, so if 2023 ever gets here, or if Marty Mcfly brought them back, well....

As to your lack of contrast, I have several guesses - guesses they are. AKB on some Sony's gets wonky - might have to chase the G2 and cathode voltages to see if any change dramatically and work back from there. Related, Sony had a problem with the CRT sockets on your model sets - but the gripe was Picture dark, not what you are seeing. Is there a possibility that is was dark, someone cranked up the G2 or Screen voltage, got a picture and left it?

Lastly, your set is famous forregulator issues (http://vdoko.tripod.com/tvs/faqs.html) - a 6V three terminal regulator would cause a dead set, and the solder around all of the IC18XX regulators could be bad as well - all seen on at least a couple of sets.

And lastly - ZD1504, an 11V Zener, will get leaky, cause an all-white screen, perhaps with retrace, and shutdown the set. Replace the original with a 1N4741A, available at Mouser, Digi-Key, or use an NTE5074A.

That's really all I have from our Sams, a brief Google search, and some thinkin'