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The switchmode in that model Kriesler was usually quite reliable but back in the day I did see a few failures. The most common cause was the drive to the chopper transistor which comprised a resistor with a parallel capacitor (can't remember the values). The resistor would go open circuit and cause the BU326 to fail. Other causes could be the various electrolytic caps around the switchmode drive circuitry. I always used a variac when powering up after a repair. I would monitor the output voltage whilst ramping up the variac and listen for the tell tale whistle of the switchmode starting up. If I didn't get any result by about 100v AC input I would stop and look for further faulty components. Obtaining a genuine BU326 these days could be difficult. Lots of counterfeit transistors about. The Kriesler sets were a high end product of the day and performed very well producing a very nice picture.
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