Thanks everyone. Replaced with an ECG/NTE538 and my display works again. It shouldn't matter but I left the "CTL"/"D" line disconnected rather than connecting it to input. I had to do a significant amount of cutting and grinding of the aluminum shields to fit the new part in there without crushing the nearby components, and I was worried that any aluminum dust I failed to clean up would cause problems. I also had quite a difficult time removing the vertical preamp board. The Youtube videos all have different model variants than mine. Anyone else who is doing the same thing should download the most recent version of the manual from the tek wiki. At first I was hampered by using an early manual that didn't include disassembly instructions, which are better any video tutorial.
