When the HV output is the same voltage as the input, usually the three transistors Q21, Q22 and Q23 are blown/shorted. Sometimes diode CR21 goes too and some resistors burn out as well as the pot.
When capacitor C26 starts to go you'll notice the displays start wavering.
An anomaly is the F2 (high voltage fuse) on the rectifier board.
Night Rider shows it as 5A slow blow. Bally realised it was an error (the rectifier diodes after this fuse are only 1 amp rating - they will blow before the 5A fuse will), so they changed F2 to 3/4 amp slow blow fuse from Evel Knievel. However... the slow blow feature was not protecting the regulator components on the high voltage section of the solenoid driver board so somewhere around Dolly Parton onwards they changed it to 3/4 amp Fast Blow. See below Dolly Parton rectifier board snapshot with engineering notes.
So make sure the high voltage fuse on your rectifier boards are 3/4 amp Fast Blow, not slow blow.