Mellotronists

charel196 wrote:

> From:  "J.K.Beresford" <j.k.beresford@s...>
> Date:  Fri Mar 21, 2003  4:12 am
> Subject:  Re: [Mellotronists] MK II station changing
>   I don't necessarily "want" this John(I don't even own a MKII).I
> have just heard some of the horror stories about tape foulups from
> the shuttle mechanism.Just was curious if anyone ever tried to
> improve on the technology yet.               Charles

_________________________________________________________

Greetings All,  Having just completed restoration work
on MK1/124, I can quickly "encapsulate" the cycling
system for you on MK1,MK2,SFX,and M300 models.

Pulse-tape is the means for stopping the motor during
"inching." A strong(saturated) signal of 1000 Hz
works in conjunction with the SSCU board.

Once the button is pressed on front-panel,a "ladder"
network determines whether to run forward or backward.
This is the time that tapes are zooming-along at 36 i.p.s.
The keylock is engaged,and indictator light extinguishes.

The circuit then "times-out" from flank-speed and then
starts to "inch". It's looking for the pulse-signal on the tape.
Inching can be adjusted for stepping width and frequency.

As mentioned above,the pulse tape stops the inching.
Keylock moves out of the way,and indicator light again
illuminates.

The rotary "sync" switch is vital as it is a  safeguard
to ripping tapes out of the machine. Eight little brass dots
(1-6, and fwd/back direction change) are contacted by a
"wiper" during movement. Driven by Reynolds or Meccano
chain. The switch must be kept clean,and all connections
to it. There are several BA9 fittings in this circuit,
2-3  each for respective keyboard. From age,wear,etc,
they can get loose and potential disaster can occur.

Other weird-science is cycling working great from one
direction,and like crap from the other. Remember , these
machines are approx.  35-40 years old. Leave nothing to
chance and check EVERY cable,connection,solder-joint,etc.

"The sum of all fears" in cycling is complete failure of
pulse detection and tapes do not reverse at extreme ends.
And the keylock not working,and someone presses a key.
.....CRUNCH!!.....RIP! go the tapes......

A "torture-test" was devised to prove reliability of SSCU's.
Pushing the Station-Select button and releasing the detent
will cause the motors to move at flank speed from 1 to 6,
reverse direction(hopefully) and back from 6 to 1. Indefinitely,
until a button is pressed-in again.  Do not attempt this with
your machine !   BTW, I've encountered all the scenarios
mentioned-above.  Now I know why my hair turned-grey,
then fell-out !

A modern approach to cycling is the use of encoding stepper
motors,and digital ckts. (simple adj. "one-shot.") And the
drivers to power the motor/solenoid. If a "cycling M400"
were to be constructed (& we've discussed this years ago),
I suspect upgraded bits would be in order.

Hope this tech-talk answers a few questions,folks.
It's not in full detail here. The unabridged versions can be
found in MKII/M300 manuals.   Cheers, Jerry the  K.