Do not turn on the soldering iron yet.
I would look for what controls the 24V output, what you call "culprit", instead of messing with the design of the PSU itself. Chances are that it is like that by design.
In other words, have you checked what are those 24V applied to and WHEN? Maybe the 24V output is for a certain function only (10A is a lot of power). We can see that the other voltages do not seem to depend of the missing 24V. Your words.
In my case I reversed an EPSON ???850 and just by reading the service manual from A to Z, I was able to use it "as is". By brain surgery I replaced the propietary logic-glue IC plus the micro in charge with a 18F452. Sure, I drawn about 50% of the schematic. The sole available schematic in the Web is a pathetically scanned one, mostly unreadable.
Any chance to compare it with another working printer not disassembled yet? I learnt a lot from the Autotest. Any chance to put it in action (do not forget interlocks) if available?
One word of caution: sensors and interlocks, better you identify them upfront, precisely to avoid them to lock any function that you could need. Eventually that is your problem now.
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Additional comment: Along the time I salvaged components from varied equipment. Lately, I started to keep the PSUs intact. I understand there are more chances that I could use them as they were built than after any tweaking or even their components separately.
Buena suerte.