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During the '70's and early '80's, the trend for many solid state color TV's was modular construction. That way, the technician could isolate the trouble to a certain module and quickly fix the problem. This was especially helpful to the tube guys who didn't know much about solid state troubleshooting. In the early '80's, most companies started going to single board chassis designs and the technician was expected to troubleshoot the set to the component level. I think Zenith was the last one to offer a modular chassis TV. In later years, that "module" was the complete chassis; but, it was designed to be replaced. Whenever possible, I tried to repair these modules to the component level, especially when the cost of a new module got excessive. When I first started fooling with TV's, a Zenith 9-160 module was around $50 for a rebuilt module. They ended up costing over $100 just before they became NLA. Now, there is almost no market for them.
I think there were two reasons that companies went from modules to single board designs. One was to cut cost and the other was eliminate problems that were caused by the interconnect system that was used with modular sets. In most brands, a common source of trouble was the connectors where the modules plugged in.
With the new flat panel TV's, things are going back to replaceable modules. With all the surface mounted stuff in these newer TV's, I'd hate to have to repair one to the component level.
I really don't think they reduced the number of circuits in newer TV's. They just made them smaller. By the '90's, there were usually two large IC's in most TV's. One IC was the microprocessor and the other IC contained the majority of the TV's signal processing circuits on one chip. Some of the later TV's even had the microprocessor and signal IC's combined into one large IC.
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