Back in June, David put up a nice TK50/TK70 FAQ on the web page,
based partly on comments from Emanuel:

http://www.netbsd.org/Library/Hardware/Machines/DEC/vax/tk50.html

In that FAQ, it is mentioned that most often the problems with these
drives arise from dirt/dust on the tacho LEDs inside the drive.  
Now, I've found two of these tacho/LEDs, on either side of the 
bobbin near the takeup reel at the back of the drive, and cleaning
them appears to help somewhat (as well as cleaning the heads).
However, I don't see any other LEDs in the drive.  Where are they?
I've got several of these TK50's now, that I'd like to give a chance
to be useful again, but I've only got one of my cast-off drives in 
working condition again.

The other question is about TK70s.  I got a TK70 controller and 
drive and I tested it by putting it in a Vaxstation 3500 (KA650, 
BA213). It worked fine there.  I then tried it in 3 different 
uVax II's, but it wouldn't work in any of them.  Is this a 
power supply issue, or a slightly different bus, or what?
I've got a manual for the uVax II, and it clearly shows the 
TK70 as an option for this box, and even has a little section
describing the operation of this drive.  My symptoms are:
the uVaxII's successfully recognize the card and drive on boot,
and I can load and unload the tape.  But when I try to read it,
I get all sorts of mag tape hardware errors, including a message
about the tape being read-only.  

Any clues would be appreciated.

Doug