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I don't remember the board numbers; but, there was a chassis used in 13"/19" sets, right after the 9-181 chassis, that consisted of a main module that was mounted horizontally in the bottom of the cabinet. To the right of the main board, there was a stand-up sweep module. To the left of the main board, was a stand up power supply module.
The next chassis was the 9-470 chassis, that was in production from roughly '87 to around '91. This TV contained most circuitry on a single module, with the video output, tuner, and stand-by power supply being on seperate modules. There was a knob-tuned version of this set that did not contain a stand-by power supply module or an electronic tuner module. This chassis also marked the end of Zenith knob tuned sets.
After this chassis was when Zenith went to a series of single board chassis "modules" and this is the era when bad CRT's started showing up a lot.
As far as larger screen sets, there was a model after the 9-181 series that contained a 9-517 main moudle, a switching power supply module, the video output module, the stand-by module, electronic tuner module, and stereo audio moudles (in sets with stereo sound). There was also the 9-516 module that was more of a single board chassis, except for the video output module and space command power supply & tuner. On the 9-516 sets, there was an electrolytic cap mounted under a metal shield in the power supply and when this cap started failing, the TV would take a long time to start up. I think this chassis was around until '90-'91, when single board modules took over.
The digital system 3 dog from the late '80's used, IIRC, a 9-700 main module that was totally shielded in a metal can.
Some of the higher end sets of the early to mid '90's used what was called a "dual module monster" chassis (power supply/sweep module, main signal module with smaller modules attached to enable certain features of the TV).
AFAIK, Zenith stuck with the modular concept on most of their color TV's until the end. Most other companies went to a single board non-modular chassis where the technician was expected to fix the set to the component level by the late '70's-early '80's.
The whole idea behind modular construction was to enable the technician to make a quick repair in the customer's home and it was also a good concept for older technicians who were more familiar with tube sets and not as familiar with troubleshooting a solid state set to component level. The main problems with modules is that they are generally costly and some modules become unavailable as the set gets older. Another problem was faulty module socket contacts that caused intermittent operation.
As far as Zenith's from the mid-to-late '80's, I find that bad electrolytic capacitors in the deflection/power supply and bad solder connections are the most common problems.
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