Thanks to a very helpful reader (Mike Senior—thanks!), the OS/2 Museum can now publish the ThinkPad Power Series 850 Hardware Maintenance Service and Reference manual in the form of a PDF. This is IBM document number 30H2383. The manual might be of help to owners of antique PowerPC portables. The PDF isn’t perfect but it should be quite useful.
Anyone who needed to take apart a ThinkPad knows that although the process isn’t necessarily terribly difficult, it is complicated enough that dismantling a ThinkPad without the corresponding HMM is a perilous journey. And no one wants to break a PowerPC ThinkPad.
There’s very little else to say, just that although the HMMs for Intel-based ThinkPads have long been available in electronic format (for all ThinkPads, even ones much older than the 850), the ThinkPad 850 HMM was for some reason never available electronically, and the HMM is nowadays even harder to find than the actual ThinkPads.