I have a HP 1720A scope here which is the bigger brother of the 1715A, but they are identical in most aspects, so if nothing else maybe I can help a little with that at least.
If you've got a service manual it might come in handy as some of the images in mine are poorly copied and hard to read. Do you know what the main differences are between the two? Thanks
Yes, the 1715A manual is pretty bad, you can easily find manual for the 1722A (275MHz, digital readout) or 1725 (275MHz, 8x10 screen, time interval) both manuals have merits, though they are very similar.
If you fail to find these, you can PM me your e-mail so I can send them to you.
To my understanding the only difference is around the input hybrid IC, not sure if the IC itself is different, but the application is for sure, there are less legs used in the 1715A, the vertical output (and everything else) is the same however.