TK70 maintenance--swapping capstans
cz at alembic.crystel.com
Fri Feb 12 16:32:18 CST 2021
Well my little TK70 here has been squeaking and it looks like the
capstans are frozen/bad. They don't move up and down and they don't spin
Fortunately I have a dead TK70 with good capstans so I figured I would
swap them. Unfortunately I don't have a maintenance manual (does anyone
have one?) so I had to figure out alignment myself. Capstan alignment
seems to be critical, if they are off the unit don't work...
Anyway here is my procedure so far to get the unit to load and unload
tapes on the bench. Not perfect, but a start....
Pulling the capstans requires you to remove the two lock nuts on top
first. I recommend you count the turns from all the way tight if
possible as alignment is critical, and the front and rear ones can be at
different relative heights.
Anyway if you didn't do this you need to adjust the rear height to trip
the optical sensors and the front one to handle tape slew.
Note: All the below is done with the unit on a bench, with a PC power
The first step is to adjust the rear capstan so the leader tape's wide
hole for the end of tape-stop marker allows light from both LEDs/sensors
to pass through. You do this by tightening the bolt down till snug, then
back off 1/2 turn.
Turn on unit, see if it unlatches. It probably will try to turn the tape
4 times then error out. Fine. Power down, back off the bolt 1/4 turn and
At some point it will open the latch. Note the # of turns of the bolt
then keep going 1/4 turn at a time till it doesn't work again (too
high). The proper value for your unit in turns is halfway between too
low and too high. Reset the bolt and verify it works several times. For
my unit the right height was about 1.5 turns out.
Then you need to adjust the front capstan. The problem is if the front
is higher or lower than the back you have tape slew errors. Start at the
level of the rear one based on the # of turns minus a bit (1/2 turn).
Then load a tape. It will load, but when you try to unload things will
go bad, the tape will just move forward onto the take up reel 4 times,
and the unit will error out. The reason is it has to read the tape as it
turns to know a tape is loaded (as opposed to the leader where it looks
for the end of leader light). If the capstans are not holding the tape
level against the head it can't read.
Each time it moves forward a bit, try bringing the front up 1/8 turn at
a time. Eventually it will speed up, that means it can read the tape on
one of those moves. It should then unload. Now you have the front
basically set. It will unload the tape, cycle it a few times to make
sure it's working.
That's where I am now. Next step is to see if it will read the tape in
the computer. I'll work on that tomorrow.
Note if you ever shine an led flashlight into a running TK50 or 70 all
hell will break loose as the system will see the light on the tape
sensor and think it has hit BOT. Even worse is if both LED sensors
trigger, then it thinks it is at end of leader and it will throw tape
Ask me how I know....
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