unreadable HP cartridges

Al Kossow wrote: Funny enough, I happened to be looking for something else and found this in the HP 9825B Desktop Computer Service Manual, page 4-12: Digital information is stored on the tape using a delta distance encoding scheme. The "1" distance is approximately 1.75 times longer than the "0" distance. The magnetic polarity is irrelevant, only the distance is important. Since the tape is driven at a constant speed, the time elapsed between flux transitions is measured. ... Reading from the Tape Reading from the tape is more complex than writing it. Variations in timing and tape speed from system to system must be accounted for. To allow for these variations the circuit detects the ratio of the "1" time to the "0" time, not the actual elapsed time. So the first thing that has to be done when reading a particular tpae is to esablish the duration of a "0" time on the tape. Tape protocol dictates that a gap will be followed immediately by twelve flux transitions with the "0" spacing. These are used to esablish a reference for the data which follows on the tape. (then there are some details about the actual circuit)