Issue with a 27" Sony from 1991

[holmesuser01]

I've got a Trinitron model KV-27TS32 set which I bought new when I worked as a repair tech for the box store that sold it. I got a very good deal on it, being an employee.

New in 1991, it has been repaired twice. The first time was to correct a known power supply problem that was brought up in the detailed printed manual that the box store provided to the techs. My set never failed, but I went ahead and replaced the parts in the kit.

The second time was about 7 years ago. The sides of the picture started pulling in about an inch from time to time with no warning. When I pulled the back of the set, I could not get the picture to pull in, so I decided that it was probably bad soldering. I went over the PCB and soldered everything around the flyback, yoke connectors and plugs, and the horizontal oscillator, including the output transistor, and driver transformer. Put it back together, and it seems to be fixed. It ran for 7 years with no shrinking.

Fast forward to NOW: It's started this same problem again. I've got a parts chassis now that died in 1993, and has all the major parts on it. I won't use the capacitors from the parts chassis in my set, though. They're too old to trust. I've looked over the chassis, and have found no bulging capacitors, and no signs of anything overheating. The only difference this time is now, the picture will pull in with the back off, and moving and flexing the chassis has no effect. The problem is intermittent. Sometimes, it shrinks on start-up, and other times, it can be hours before it shrinks for a moment, and returns to normal.

Other than this issue, the CRT is strong, and it produces an excellent picture. I want to see how long this oldie will keep going.

I have a copy of the service manual, and can't locate the box store book that I had for so long. Have any of you seen something similar to this problem on these sets? I have never touched the set-up menu, other than to reduce the green screen level slightly about 18 years ago. If it no longer looked perfect, I'd dump it/part it out.

I appreciate any insight here.