An older, discontinued scope? Geez, you make me feel old. That product came out after I left Tektronix. Makes the 465 and 7904 on my bench look like relics!
The "analog" scopes weren't that difficult to repair. As the scopes got "newer", Tek started adding digital control to the analog functions to include readout parameter generation, digital display of delay time and provision for auto set-up. Because of that, the malfunction of the digital control can cause total scope shutdown as easily as can a defective analog section or power supply!
Regardless of the type of scope, whether tube, transistor or integrated, analog, hybrid or digital, the first check is ALWAYS the power supply. Just because it appears to "light up" doesn't mean that all of the supplies are working properly. Most Tek scopes of the non-DSO variety have LOTS of power supplies. e.g., the 7000-series has +130, +50, +15, +5, -15 and -50 not to mention the high voltage and PDA accelerator voltage.
Dean