If you've ever tried adjusting convergence on an old school CRT colour TV, you will know the definition of "iterative insanity"!
I have. That is exactly the kind of experience I'm talking about. You over-tweak one just too far and you're back at the beginning.
BWAHAHAHAHAHA!!!
You simply have not lived until you've done survived the unholy convergence rituals necessary on a old Pioneer or Hitachi CRT projection set with analog panel.
mnem
*speaks soothingly to the PTSD dwagon juddering in the deepest recesses of the tinkerdwagon's memories*
"there, there.... it's okay.... we'll never, ever have to do that again... we promise..."
At least those are all low power. In a typical british valve colour TV the perset carried signficant power. Smoe were wirewound. Most ran hot. Often th platis would break as soon as you touched it and a cooked preset would jump al over the place...
Oh, these were just a different kind of evil. This one, the high-energy was all in STK amplifier packs under that huge heat-sink... and they were a really bastard kind of evil where they would go leaky, or the deflection coils would develop a few turns short and make the STK go leaky or... short intermittently... or sunspots... or whatever...
Anyways... the only way you could figure this out on some models was to spend the time doing the convergence 2 or 3 times and still not be able to get it in spec. The deflection coils were so loosely wound they were ringy AF even on a good one, so that wasn't a tell... and you can't inject a signal into one STK and observe the output with it hooked up due to physical constraints and how the loading of one STK affects the others in the chain.
This was the beginning of "board-level repair only" factory service procedures on these things, and for good reason. You could spend days locating a single faulty STK, and replace it for a successful repair, only to have its neighbor fail in exactly the same way hours or days later due to now getting full current/voltage that previous failed STK protected it from.
Eventually the service suppliers would develop "repair packs" to replace all the STKs and most common fault/burned out capacitors/resistors shotgun-style... but those were very often clone "STKs" with high mortality rates as OEM ones cost 1/3 the price of a complete board each.
Then you had problems with bacterial infection in the coolant... reflector mirrors that were cigarette smoke magnets, only you couldn't clean them safely because the mirroring is on the outside... plastic lens assemblies that would craze or go cloudy because of all the IR and UV radiation from overdriven CRTs that eventually developed burn-in no matter how careful you were with source material and...
Honestly... CRT projection sets were just a shitshow; even the "good" ones. One of the first
"eWaste the day it was made" technologies; seriously.
mnem
and of course, all so you could rot your brain more efficiently...