ard at p850ug1.demon.co.uk
Tue Jan 17 17:19:15 CST 2006
> Ok, I was so curious that I did the test with the servo head
> disconnected. It is sure a different movement!
Excellent. This means it's reading something from the servo surface, and
that your pack has not been bulk-erased.
> First let me describe the head movement in more detail.
> In stand-by, the heads are in what I call the "home" position.
> When the movement starts, the heads come out of the home position
> at a moderate speed, and when the heads are at "track 0", the
> speed drops and the heads move at a slower speed towards the
> centre of the pack. Then the movement stops, and starts at that
> same slow speed towards the home position. However, the heads
> stop at what I call that "track 0" position, and stay there
> until I press the LOAD button again. Then the heads move *fast*
> to the home position.
One thing you should realise at this point is that the RK07 positioner
servo is complciated. No, correct that, it's _very_ complicated. I have
the printset (is it on bitsavers?), I remember going through it once.
IIRC, there are actually 3 feedback loops. One from the error signal from
the servo head when it should be on-cylinder. One from an optical
transducer (load/unload?). And one from a magnetic velocity transducer
inside the magnet assembly.
> Now with the servo head disconnected ...
> To quote 'Allo Allo': "listen very carefully, I will do this
> only once", well sort-of :-)
> The heads move at the moderate speed to "track 0", but stay at
> that speed while the heads move to the centre. That movement now
In other words it's not picked up any signal from the servo surface. The
head movement is controller by ther other 2 loops, which explains the
fast, but not ridiculously fast movement.
> looks a lot faster! At the centre the movement stops, and the
> heads move at that speed (or was it even faster?) not to the
> "track 0" position, but to the home position.
It's failed to find any servo data. I think the optical sensor indicates
it's got to the spindle, so it does an emergency unload and gives the
So, looks like the drive is basically working. If there is a fault, it's
in one of the relatively simple sections..
More information about the cctech