The HV oscillator's power transistor is mounted to the rear panel. Since its collector has 40 kHz with tens of volts peak-to-peak a decision was made to add metal plating to the transistor's Bakelite cover to prevent EMI. Unexpectedly, the outgassing from the Bakelite caused the metal plating to blister, which shorted the collector to the case. When this problem was discovered, the metal plating was removed from the design. In hindsight, the designers didn't believe the plating was necessary in the first place.
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