'Nothing to check voltage' meaning, no reference manual or service manual showing the test points and the proper voltage ranges for them?
Or, simply, no volt-meter to check voltage with?
The process has to be painstaking. TVs are complex systems, which can be deranged in odd and unexpected ways by one single component failing. It takes time and effort to find that component - even at the board level.
(Also, in older TVs, connectors can get dirty. No amount of board-replacement will cure it if the connectors to those boards do not communicate. ...And there is the case where a power supply voltage is defective, from the power supply, causing defects in other parts of the TV. And, worst of all, a shorted board or component can load down one power supply voltage, causing perhaps a puzzling variety of problems esp. if the p/s. itself is damaged by this... not usually, but it can happen.)
My apologies. I'd really like it if I could make this simpler. If you would prefer another Expert to take this on, let me know.
And, service manuals are available - sometimes for free, usually for a small amount if they cost something. Would you like one?