This goes back to my electronic service days.
RCA decided they needed to be different from everyone else. TV tuners at the time had all the tuner electronics on a board inside a shielded metal can. So RCA mounted the tuner parts to the main circuit board and then soldered the metal shields on top of them. They used this system for about 5 years in their sets. So far so good. Unfortunatly they also ran the ground connections from circuits on one end of the main board to the other side thru the tuners metal shield. As the set heated and cooled the main board flexed and eventually cracked the solder connections on the shields. This caused problems ranging from no audio, all sorts of tuner problems, vertical circuit troubles and dead sets. The engineers came up with a fix. We were to use a "special" flexible solder to fix the problem. The solder came with special flux and had to be heated to 890 degrees to melt. The metal shields were made of steel, copper or zinc, zinc melts at 900 degrees, and all shields were zinc coated so you couldn't easily tell what type you had.

After repairing hundreds of the sets we received another bulletin from RCA. The flux they sent in their kits would eat circuit boards if not completely washed off.

At the last RCA service training I attended, the instructor came in and said "we will not talk about tuner problems. You're all gonna put your kids thru college on that one so shut up"