Yet another idea for recovering the data from Series80 tapes

[Joe R.]

At 04:28 PM 10/29/05 -0400, you wrote:
>Background:
>
>The problem with the old HP 9162-0061 data cartridges is that the
>magnetic coating peels off from the (transparent) tape causing the
>machine to stop accessing the tape with an EOT warning. This is
>actually very good news because it means that the damage is localized
>(a few mm of tape with scrapped off magnetic coating).
>
>BTW here is a picture of a damaged tape:
>	http://www.series80.org/Articles/DamagedTape.jpg
>
>My guess is that the magnetic coating gets scrapped off the tape
>during fast motion (rewind or fast forward), so presumably if you
>simply advance the tape over the heads at normal read speed (10 ips)
>the tape will survive for a single pass (there are two tracks on the
>tape, but since the head is not moving, I assume that you can read
>both tracks at the same time).
>
>Now since we have only one attempt, and we are likely to encounter errors,
>I do not want to have the Series 80 firmware involved in the process.
>I would like to simply record the info (via a PC) to a .wav file and then
>process that file to see if anything can be extracted.
>
>Proposal:
>
>To do this I would need to manually rewind the tape till the BOT sensor,
>mount it on the tape drive and advance it past the read/write head
>till I run out of tape (tape unspools from the supply reel).
>
>While this is going on I am recording the output of both heads via the
>audio in port of my PC sound card (maybe use two separate sound cards to
>avoid cross talk?).
>
>Data extraction rig:
>
>1) audio connection: what kind of set-up would be required to connect the
>heads to the audio card. From the schematics I see that there are essentially
>three connections to each head:
>	Head 0:	H0, CT0, and HC
>	Head 1:	H1, CT1, and HC (HC is common to both heads)
>But I am not sure what these are used for.
>
>2) running the tape at a constant 10ips. There is a circuit that uses
>the tachometer wheel to control the tape speed, but again I am not sure
>how to program (?) the tape controller IC (U1) to move the tape.
>(I may need to disable the BOT/EOT sensors, but that should not be a
>problem).
>
>I am lucky to have a 9915A as my test bed which allows far easier access to
>the tape drive mechanism than the HP-85 (and does not have these evil
>ribbon cables).
>
>Unfortunately I do not have a scope, but I can borrow one for a short
>period if necessary. I have a logic analyzer.
>
>-------
>
>Another idea that just came to me as I was re-reading this email, is that
>I can possibly allow the read/write IC (1820-2418) to do the analog to
>digital conversion for me, ans simply read a stream of bits (with a time
>reference). Is this approach better/worse? Perhaps I can do this in parallel
>with the audio recording. (if the 1820-2418 is only able to sample one
>track at a time, I can use another 1820-2418 for the second track).
>
>Any suggestions are welcome.


   Both ideas sound do-able to me. It might also be a good way to find out
how HP "protect"s the program tapes and possibly duplicate them.

   Where are you located? I have a couple of spare scopes and I might be
presauded to loan you one. But I'll have to do some checking to be sure
that that these specific models can survive shipping.

     Joe