Yet another idea for recovering the data from Series80 tapes

ard at p850ug1.demon.co.uk (Tony Duell) wrote:... Aha! There goes my original hypothesis. Well, that is relatively easy to check. I took apart two old tapes and found the following: Assuming that the tapes were rewound before storage, there are two stretches of weakened magnetic coating on both tapes I looked at; the first was short while the second longer. These correspond to the length of tape in contact with the drive belt In http://www.series80.org/Articles/tape-cartridge-lr.gif you can see that on the take up reel (left) there is less tape in contact with the drive tensioning belt, while on the right hand reel (which has most of the tape and hence a longer radius) more tape comes in contact with the belt. Looking closely at the belt, I can see remnants of tape oxide stuck on it (in fact its stuck so well, I could not remove it). So how come we get an EOT error when using these tapes? The tape has tiny holes near the beginning and end signifying BOT and EOT. (BOT) (EOT) +-------------------------- .... --------------------------------------+ | | | o o o o o | | | +-------------------------- .... --------------------------------------+ I assume that the first hole signifies the end of the data region and then if the drive sees one hole its EOT, while if it sees two holes (prob. more than one) its BOT. So when it sees the blank region, it interprets it as one hole and reports end of tape. Using a marker to paint (on the back side of the tape) over the region does not work, since the markers I tried allow some light to go through. I stuck a piece of splicing tape and that took care of the hole, but I got a DATA error. I guess the 85 needs some of the info that is missing I have also noticed that the tape does indeed stick onto itself on the right hand reel, but if you unwind it slowly you can get it unstuck without damaging it. I assume that conditioning the tape by warming it up before use may reduce this sticking problem, but I still would not want to fast wind a tape in that condition. Given the above, I am even more confident about data recovery, as we may be able to use the existing tape mechanism of the 85 to read the data by skipping the regions that appear blank until the tape un-spools and the drive stalls. This may end up being a software project after all :-) So the new plan is to see how I can get the tape moving at 10 ips (I'll look at the 9815 diagrams) and see how I can tap the output of the read/write IC (1820-2418) to get the bits from the tape. If this does not work, I'll have to get somebody to help me built the preamp for the heads. I wish I could understand this infernal assembly language of the 85 so that I could look at the internal routines that access the tape for ideas. ------------------ ard at p850ug1.demon.co.uk (Tony Duell) wrote: There was a program on the Series-80 User's Library (8291029) that allowed retrieving 9845A SAVEd programs. The program was for the HP-85 and did not specify any ROMs or peripherals. You may infer hand, the 9845 used dual directories (the second one was a backup) per tape while the HP85 only uses one, so this may be an indication that they are NOT compatible. -------------------- "Joe R." <rigdonj at cfl.rr.com> wrote: I would guess some bit in the directory entry (like LIF volumes), but if my plan works, we'd be able to copy tapes at the bit level so HP's protection would be irrelevant. Thanks for the offer, but I work at the College of Engineering here at Drexel, so I can find a scope (as well as someone who can tell me how it works :-) -------------------- So, back to the drawing board... **vp