This video describes troubleshooting procedures of a non functional Tektronix 515A oscilloscope . It had out of spec power rails and defective high tension output. Many older tubular capacitors had excessive leakage and were replaced. Four vacuum tubes in the power supply were replaced as well as the three HV rectifier tubes. I was unable to get the high tension voltages within spec. I plan on replacing the high voltage vacuum rectifiers with silicon diode replacements. This may reduce the loading effect on the high tension transformer improving operation.