The 5V is made on the bottom layer, IC209, from the "15V" of the secondary seen at TP201 with respect to chassis ground.
Are the resistor values blurry or too small or what is the problem? The schematics are image files that you can right click and save to your device, then use an image viewer and zoom in if necessary.
i will repost the last schematic with notes about the switching threshold voltage levels.
The set point reference is developed from the 5V and the feedback resistor from the output to the + terminal causes a hysteresis action to filter out oscillation as the signal passes thru the set point on the way up and back down. When the signal matches or exceeds the V Threshold(Hi) it switches output to the Hi state; Then when the signal is headed back lower than the low Threshold, the output switches to the Lo state.
ref from application notes
For the -C and -D comparators, the "Signal" is level of the Output 12V to decide something; the -A and -B are looking at the TP201 "15V" supply as the "Signal" to decide when to do something. There will be a certain time delay as the secondary voltage is coming up; the comparator outputs can be used to regulate or turn something on or off based upon the voltage level of the "15V". i don't know what all that is yet, there is still a lot of stuff to sort thru in that LV section.
The -C leg is what was traced earlier in crude form to determine that it was one of the causes for the PWM to start or not by commanding pin 8 of IC201. Both Pins 8 or 9 of IC201 can be used turn off or restart the PWM switching.