Terry, were there really a TU79? I've only seen/heard/touched the TA79, which talked STI. A TU79 would, I assume, be the Massbus variant. I've used TU78, but it would be cool if the TU79 actually also existed.
I was using "TU" as the generic, as the 77 only came in Massbus TU77, the 78 came in Massbus TU78 and STI TA78 flavors, and the 79 only came in STI TA79.
I'm not sure if you could mix and match 78/79 drives as secondaries* with the other model as a primary* - all of my drives were primaries.
I did have a "TU79" which was a TA79 drive with a TM78 formatter in it (which is the reason I think mix and match might be possible). I did that conversion because at the time I only had SDI cards in my HSC50 - subsequenly I won a pair of universal (disk or tape, depending on microcode) controller cards for my HSCs at a DECUS Symposium. Prior to the universal cards, cards were either SDI or STI (presumably just a different set of PROMs).
* primary/secondary used instead of the period-correct terminology due to #BLM
Our TU77 and TU78 worked pretty well in picking up tape when autoloading, but they were far from perfect. Could maybe have used some of your tlc.
We actually still have those drives. I should try getting a TU77 running, as we don't have any running 800 drive at the moment.
The main improvement was a rubber foam gasket in the well where you mounted the tape, located between the Easy-Load II seal and the air port on the drive. The drives originally shipped with no gasket. They also shipped with the wrong airflow through the air port, but that was a less important part of the fix. DEC only made 100 FCO kits for a field population of ~6000 drives and it was an "Improvement" FCO, meaning the drive had to be on a Field Service contract and the customer had to complain in order to get the FCO. The most famous mis-categorized "Improvement" FCO was the power harness in the BA23, which tended to set the whole chassis (and sometimes a whole car assembly line) on fire.
The TU77 never officially got the load fix FCO, although the same kit works fine on a TU77.
The "whopper" TU78 FCO that took 3 tries for DEC to get right was the read-after-write soft error fix at 6250 BPI on TU78s. The boards shipped with the wrong capacitors. Rev A of the FCO replaced the capacitors, but positioned improperly. Rev B of the FCO fixed the problems with Rev A. Rev C added a shield that was forgotten in Rev A and Rev B. The capacitors and shield weren't the only problem - the Write and Preamp boards needed to be replaced, along with the Write to Preamp cable. The Read board needed modification, as did the 9 M8950 boards in the formatter and their ground wires. All in all, a total cluster-flip(chip).
