Just to make sure, you know that the Vf of those high voltage diodes is often quite high since they just stack up a bunch of regular diodes to make them?
I'm worried you're barking up the wrong tree thinking the secondary is open when it's not.
Hi Paul, thanks for the reply. The secondary that was open circuited is the +75volts winding, not the HV winding. The +75volt is very essential for this display board to function.
For those that are interested, I have managed to measure the ohms of the HV feedback resistor. It is 300 Mega Ohms [you cannot measure with multimeter]. This resistor alone is not cheap, you can check ebay. During the course of it, I have learnt a couple of things. For example the HV windings in wound in a special bobbin that separates it into many sections so that internal arching can be avoided.
Actually, I have already installed with LED TFT screen, high resolution. As it turns out, a piece of cake and the display is very vividly sharp and clean and I have come to accept it, though, you know, the feeling that the scope is no longer the original... But as it saves a whole lot of space, reduce heat and current consumption, I would recommend the upgrade to LED screen actually.
But I will continue to wind the HV transformer out of interest and build a special winder to tackle the 0.02mm magnet wire. The cost would not add-up, if you ask me... Cheers!