The head is the mechanism that touches the tape and reads and writes data, so it is absolutely critical; in the case of the Ampex FR-900 tape drives, the heads were not manufactured after 1974, cannot be replaced, and can only be refurbished at great expense by a single small company. After another month of repairing and replacing parts, testing and tuning mechanisms, the project got the first solid result that the tapes were good. Each tape starts with a short standard-format audio clip of the operator, and the tape drives were able to read the audio signal. (Hear a sample of the audio.) This does not use the video heads that are needed to read the Lunar Orbiter data off the tape, but this demonstrated that the tapes had not deteriorated and that many of the sub-systems of the tape drive were in good working order. The documentation for the tape drives was substantially incomplete, which kept the team from understanding the right way to repair, maintain, and use the tape drives. The search for documentation has been extensive and usually disappointing, as it often turns out that retired or elderly engineers have just recently cleaned out their garages. Posting to a blog, Dennis Wingo said, "I cannot tell you how many times we have heard similar stories of recently tossed manuals over the last six months". At just the right moment the team heard from a friend of a friend that a mother lode of maintenance documentation stored on aperture cards (microfilm embedded in computer punch cards) had been saved by the retired head of Ampex field engineering. This documentation would make it possible for the team to understand the correct procedures for repairing the tape drives and aligning the mechanics. At this point in the restoration, the demodulation of the tapes had become the biggest issue. The team was not sure if the demodulation board that came with the system was the correct one, if they needed a different one, or if they needed this one and another one. At the same time, they discovered a tape, which, from the audio clip at the start, sounded as if it contained a demodulated recording of one of the images. This was a lucky break, as it meant that a demodulator would not be needed to generate images from this tape. If the team could rescue this image, the project would prove "that the drive can be refurbished to the point of reliably playing a tape back". Work continued, and the team coined the term "technoarchaeology" to describe the process of researching which tape contained what image.