Adjusting transformer feedback frequency

[gkmaia]

I've got a scope I am working on for quite a while and the HV transformer was dead so I had to make a new one.

As I have two of these scopes I toke the transformer of the working one out and reverse engineered it. When tested with 60Khz frequency and 10% of the actual voltage they output exactly the same values.

The thing is, when I tested the transformer in circuit the feedback winding produced the correct voltage but its frequency was 300khz and because of that my R457 in the RC is starting to smoke.

The right frequency is 60Khz.

I am wondering is there is a way to tweak this circuit to better work with my transformer and reduce the frequency from 300khz down to 60khz.

Is it something to be done at R/C 457 or on the feedback drive circuit prior to C455?

Or is C455 that defines the frequency while charging and discharging? If it is... adding capacitance will slow the cycles?

[tautech]

I'd strongly suspect the high value HV divider resistors on the secondary side have drifted and the resultant voltage feedback is now too high causing the primary switching to operate outside its design parameters.