I recently bought a Heathkit IT-28 Capacitor tester in a sorry state and ended up doing a complete strip down and rebuild. Was an interesting experience as i had to follow the assembly manual as though i had just bought the kit back way back when. A few thoughts on the experience..
You get a single page diagram that you have to refer back to over and over again. A line in the instructions might read (connect a 3" wire from switch R-3 to socket V2-7) and you have to flick back to the diagram to work out those locations, then go find your place again in the page of text. Thankfully i have the modern ability to print the page and keep it in front of me, but even still, you end up jumping back and forth which makes it so much easier to get it wrong.
Also all the diagrams are hand drawn illustrations, vs today where Bottlehead gives you a nice crisp colour photograph next to each instruction step. Pictures really do speak a thousand words.
Troubleshooting, no final checks, no voltage checks, no resistance checks, just a calibration procedure. They do mark some voltages in the schematic so you can go find those and compare, but for the most part, you are on your own.
What if it still won’t work? Well that’s where i am currently, half of the unit works, the other half has me completely stumped. I could write to Heathkit for support, if it were the 1960's. Imagine having a support forum, what an invaluable tool that would be, being able to talk directly to the folks who designed the thing, and could troubleshoot it remotely in a few short posts. What an amazing concept that would be