Also, a general question for the CRT guru's.
Why on this model the HV is driven from the horizontal drive anyway? I've looked at other CRT schematics (way more simple ones) and the HV drive has it's own oscillator. Here is an example, the HV drive in this one is driven by a 555.
The Monitor in the above link doesn't look like a raster display,it is probably a vector display as quite a few arcade game Monitors are.
No continuous Horizontal deflection waveform means the drive for the EHT has to come from somewhere else.
The vast majority of analog CRT type TV sets & Monitors obtain EHT
* from the Horizontal Deflection Circuitry,for quite logical reasons.
(1) Magnetic deflection CRTs require quite a lot of power to scan,so you already have an appropriate stage in the TV.
(2) The Horizontal output Transformer is a necessary part of the deflection circuitry.
I'm not going to give you a rundown on all the reasons it is needed,but the information is available in
real books!---the Internet sucks!!
Hint:- Think about where the electron beam would point if there was no deflection.
As it is there,it makes sense to wind an additional EHT winding on it.
In fact,most TVs & Monitors have
another winding,(which used to be called the "boost HT" winding in the vacuum tube days,but is still used with Solid State) which provides a higher supply voltage for the Vertical & Sound outputs than that available from the normal power supply board.
(3) Any interference caused by the EHT circuit is in phase with the video,so is much less visible than a "free-running" supply.
Looking at the schematics in your original posting,the third one looks to be of a different unit altogether--the component numbers don't match!
From #1 & #2 it seems that Horizontal Drive also goes to IC9015 ( the "Chopper Drive" IC)via Q9058.
As "Chopper" sounds a lot like something to do with the main SMPS,it appears that the switching of that unit is synchronised with the Horizontal signal------again to reduce interference.
It is common with this sort of circuit to have a temporary "start up" power supply which supplies a reduced supply voltage to the Horizontal Oscillator circuit (part of IC9001 in this case)so it starts,feeding H drive to the Chopper Drive IC,which in turn starts the SMPS.
It would seem that the SMPS is not starting,& that the "start up" supply has some sort of "timeout" circuit,so it stops after 500ms.
* ( That is what it is most commonly called by people familiar with such equipment --EHV may be more Politically Correct for some reason)