To: analogue@hyperreal.org,
From: Christian Hofmann chris@scp.de,
Subject: Memorymoog tuning procedure (long)
Date: Thu, 4 Jun 1998 15:40:53 +0200


Hi,
as promised, here's the Memorymoog calibration procedure. You will need
a lot of time and patience for this!

Opening the case
----------------
Important: don't turn the MM upside down before unscrewing, it's best to
leave it in its normal upright position, just slightly lift as necessary.
Remove 3 screws at the back, and on the bottom only 3 each at the left,
right and front side. The other screws hold the pcbs etc.
Then, slightly lift the panel at the back and gently slide forward to
bypass the potruding keyboard.
A word of caution: there are some electronic components which can be
damaged by electrostatic discharge, so when touching the pcbs (e.g.
lifting the upper ones to get to those below), it's best to keep one
hand on the grounded metal case.

Identifying the voice boards
----------------------------
All the voice boards are located on the right side, 2x 3 stacked together.
Top left=1, top right=2, middle left= 3, middle right=4, bottom left=5,
bottom right=6, these are the numbers from C7 calibration menu, see below.

Important: let the unit warm up for about 10 or 15 minutes before doing
any trimming. And if you leave the windows open - if there's noticable
air flow, you can forget all the calibration, since it will randomly affect
the oscillator temperature.
It's bad anyway that you are forced to do the calibration with the MM
case wide open. It would have been so much better if all the trim pots
were at the back, accessible thru little holes, but they haven't done it
that way. Sigh.

Using the calibration menu for each oscillator
----------------------------------------------
Press
C,
7,
Enter,
Enter,
(display shows "VOICE?") press voice number digit ( between 1 and 6),
(after 1 sec. display shows "OSC?") osc. number digit (between 1 and 3)
Now 3 hexdecimal numbers for the selected oscillator are displayed. They
correspond to the 3 trim pots RANGE, SCALE, HI as labeled on the pcb. (If
the display shows "DEAD OSC" instead, don't panic. In most cases it's not
really dead, but it's too far out of range. Since I haven't had this yet,
I would have to look up what to do.)

Tuning
------
With the calib display described above, you can adjust the trim pots.
Although these pots have some 10 or 20 turns, it may be a matter of small
movements. It's a bit fiddly, since you can't read the display well while
the panel is up (to reach the trim pots). It's important to keep this
adjustment order:
1: Adjust SCALE pot to approx. make the 1st and 2nd display numbers
equal.
2: Adjust HI pot to make the 3rd number equal the other two
3: Adjust RANGE pot to make the 1st number 7F.

Notes:
- hexadecimal means counting 70 71 ... 79 7A ... 7F 80 81..., so there
are 6 numbers between 79 and 80 etc.
- the turning directon to affect the numbers differs in a weird manner
between the 3 oscillators.
- the numbers displayed will jump +/- 1 or 2 digits, that's nothing to
worry about. What _will_ drive you mad: once you have reached the desired
numbers, it may drift away within minutes. That's when those 4 letter
words come in...

This procedure has to repeated for all voices and all oscillators.

Hope this helps, if you still need some advice, feel free to ask :-)
Christian