Tech Tips

I have a saying: "there is nothing worse than an expert." I say this because the expertise acquired between the time a guy gets enough information to be considered somewhat knowledgeable and the time he considers himself an "expert" never seems to be enough.

The following is what *I* do with Mellotrons and Chamberlins. Some other guy might do it differently and even better but, he's not writing this. Besides this info is free. The empirical method reigns supreme here, if you have a tip you'ld like to share, please e-mail. The more we know, the longer these lovely instruments will be around.

Taking things apart.

M400's and MkV's are simple machines. You can strip a 400 down to its basic components in less than an hour.

Remove the keyboard and tape frame.

The front and back panels are usually held in place by a nylon screw and a great deal of friction with the edges of the panel. Often a poorly executed refinish job will exacerbate a bad fit. Sand as needed or resquare the panel when and if you refinish the 'tron properly.

The top and cheek blocks are held in place by: A.Brass fasteners B. Plastic fasteners or C. Gravity. The brass fasteners work the best. If you find it hard to press fit the piece into place you can adjust either the position of the fastener (usually correct to begin with) or adjust the tension screw on the female piece of the assembly. There is a spring loaded ball that snaps the male bit into place and this can be too tight and or dirty/corroded. A small drop of lubricant won't hurt matters any. If you have the ill fitting plastic type, replace it with a new brass one. We can supply these now. Gravity works great but, only in one direction.

The pre-amp panel is held in place by two wood screws in the back. You must first (very carefully!) disconnect the head block lead, the curly ground wire to the chassis, the multi-pin connectors going to the power supply, and the output lead at the power supply. Disassembly of the pre-amp block as follows: Remove the knobs, power switch and track selector. Remove the back cover of the pre-amp box. Carefully remove the foam block holding the pre-amp and line amp cards in place. Remove the cards (good time to clean the edge connectors). Remove the screws holding the box to the panel block. The aluminum face plate is fastened by some very easily damaged screws. Be sure and use the proper sized screw driver and a great deal of care if you remove this panel. Aluminum scratches easily.

You can now remove the 6 large wood screws from the main frame of the chassis and remove the entire assembly. If you are refinishing the cabinet, you'll want to remove the pedestals (feet), the output lead/connectors and the brass cabinet fasteners.


Motor positioning and belt tension-

The M400 Essex motor is mounted in an adjustable plate. There are 4 bolts holding the entire assembly to the side board and 2 bolts affording adjustment. Facing the back of the cabinet, the bolt farthest from you is a pivot. The bolt nearest you can be loosened allowing the motor to swing vertically on this pivot. This is the only way to adjust belt tension. You should have approximately 1 in. of side to side play in the belt. There is a fairly broad tolerance here however. If the machine stalls at startup, the belt is probably too tight. If you find you have droopy chord syndrome, you may have a slipping, loose belt.

Another common problem with 400's is that the board on the pulley side will warp. Novatrons and Sound Sales modified Mellotrons usually have a wooden support block at the bottom of the board mounted to the cabinet side. This "shim" is an easy fix. If you have a great deal of belt noise, this could be the problem although I have also commonly seen an adjustment of the pulley on the motor shaft needed.

If you do find that you need to adjust the position of the pulley on the motor shaft, you may also need to move the tach head as well. The tach head bracket is adjustable, move the head so that it's center is near the tach wheel. Also be aware that the belt will last a lot longer if properly positioned.


SMS4/MR Installation Instructions


1-2 The SMS4/MR is essentially an SMS2/SMS3 Motor Speed Control but with improved temperature and load stability. The layout and form factor follow the SMS2/SMS3. The SMS4/MR uses the same connectors as the SMS2 (the SMS2/SMS3/SMS4/MR use identical motor connections). The SMS4/MR is a direct replacement for the SMS2. As a replacement for the SMS3, only the Power/Speed Control connector must be replaced. This document is primarily written for replacement of the CMC4S, CMC10, CMC10FD with the SMS4/MR.


SMS4/MR Motor Speed Control
10-pin edge connector
50k Potentiometer (Pitch Control)
Installation Instructions


1-5 The following tools are needed:

25 watt solder iron
Flatblade screwdriver
1/8" drill
Adjustable wrench or pliers
Hack Saw
Wire cutters






2-2 Preparation

2-3 The following section prepares the Mellotron for installation of the SMS4/MR. Since the power supply must be slightly modified, this a good time to perform the Low Noise Modification as described here and in the Mellotron 400 Service Manual. If the modification has already been performed or you do not wish to perform the modification at this time skip the steps as indicated. The Low Noise Modification can be easily performed at a later time.

( ) Disconnect the power cord from the wall and at the back of the Mellotron.

( ) Remove the top cover, front and back covers, and both keyboard side

( ) Remove the keyboard and set aside, place it either top down or stand it up
in a safe position. Do not lay it on the pinch roller/pressure pad side!

( ) Remove the tape rack and place it in a safe position.

( ) Remove the mounting screws and all cables from the power supply. Remove the power supply.

If you are skipping the Low Noise Modification, go to Section 2-4.

( ) Turn the power supply upside-down and place it so the heatsink is on the left.

( ) Note the two blue capacitors on the left. Loosen the mounting straps on
these two capacitors and remove them.


In the following steps, some power supplies have been found to not have
three wires going to the larger blue capacitor or wires that don't go to the
places described. While these units are rare, DO NOT PERFORM THE
LOW NOISE MODIFICATION if the wiring on your unit is not the same.
Contact Mellotron Archives for further information. This modification is not
necessary for the SMS4 installation.

( ) The larger capacitor will have three black wires going to the negative
terminal. One of these wires will go to a ground lug under this larger
capacitor. Leave this wire, but disconnect the other two from the capacitor.
Leave these two wires free for a moment.

( ) The smaller of the two capacitors will have two black wires going to the
negative terminal. Again, one wire will go to the same ground lug under the
larger capacitor. Leave this wire and disconnect the other wire.

( ) You should now have three black wires free. Strip each end and solder all
three to the ground lug under the larger capacitor.

( ) Replace the capacitors in their respective straps and tighten the screws.

( ) This should significantly reduce the hum and noise in the output.

2-4 Power Cable Modification for SMS4/MR Installation

( ) Position the power supply so you are viewing the heat sink and it's

( ) Locate the two red wires going to the two diodes mounted to the heat sink
under each transistor. Unsolder these two red wires from the diodes.

( ) Turn the power supply upside down and pull the red wires through the
rubber grommets. These two wires will be soldered to a new location.

( ) Solder these two red wires to pins 2 and 3 on the 9 pin round socket. The
wires are interchangeable, so either wire can go to either pin. If necessary
pull the red wires out from the wiring harness as necessary to provide
enough length for connection to the 9 pin connector. Save any extra pieces
of wire.

( ) Remove the two orange wires going to the fuse holder located at the front
of the power supply.

( ) Remove the four screws securing the transformer cover and remove the

( ) Locate the two red wires and the one orange wire going to the transformer
outputs labeled:

22.5V (red wire)
0V (orange wire) The colors may vary!
22.5V (red wire)


This side of the transformer faces the heat sink. There are three outputs on the right side of the transformer. The center output is the 0V.

( ) Pull the orange wire that is connected to transformer 0V output from the wiring bundle under the power supply. Once that wire is free, insert it back
through the grommet and pull the free end out towards the 9 pin connector. This orange wire will be soldered to a new location.

( ) Locate the white wire going to pin 8 of the 9 pin connector and remove it.
Wrap the free end of the white wire with electrical tape or shrink tubing. This white wire is no longer used.

( ) Connect the orange wire from the 0V output of the transformer to pin 8
of the 9 pin connector.

( ) Wrap the free end of the other orange wire (previously going to the
fuse holder) with electrical tape or shrink tubing. This wire is no longer used.

( ) Replace the transformer cover using the four screws.

2-5 Front Panel Modification (Speed Control)

( ) Using a hack saw, remove 5/8" from the shaft of the replacement 50k

( ) Remove the PITCH knob from the front panel.

( ) Remove the two screws securing the front panel to the cabinet.

( ) Turn the front panel over and remove the four screws securing the
PITCH control to the control panel.

( ) Note the connections to the PITCH control. Unsolder these wires and
solder them to the corresponding pins of the 50k replacement potentiometer.

( ) Re-install the new PITCH control by performing the reverse of the
above steps.

2-6 Power/Pitch Control Connector Installation

( ) Remove the nut from the mounting bolt securing the top of the old board
and pull the board out of the edge connector. This connector will not be
replaced since it goes to the motor and requires no changes. If there is
a metal bracket for the connector, remove the bracket and the cable and let the connector drop to the bottom of the cabinet. (For those of you with earlier Mellotrons using a CMC4, it is mounted differently. Fake it.)

( ) Replace the nut and black wire removed in the previous step and tighten.

( ) The CMC10 will have a cable attached to it. Cut this cable from the pins

( ) Locate the 8 pin connector that came with the kit.


If the connector is a double row type, either bend the pins together (1 to A, 2 to B, etc.) or make sure you solder to the correct row, since the SMS4MR has traces on only one side. Refer to the attached SMS4MR Component
Locator for what is pin 1 on the SMS4 (J2).

( ) Locate the grey shielded cable in the cable cut from the CMC10 board.
Connect the red center conductor of the shielded cable to pin 1 of the

( ) Connect the shield of the grey cable to pin 2.

( ) Pin 3 is empty.

( ) Pin 4 is empty (key).

( ) Pin 5 is empty.

( ) Connect the grey wire to pin 6.

( ) Connect the black wire to pin 7.

( ) Connect the red wire (not the shield center conductor) to pin 8.

( ) Using a small screwdriver, remove the cap from the 9 pin connector
and remove the cap. The connector is marked with numbers next to
each pin. Verify or move the following wires to the indicated pins. You
can change the wires in the connectors by heating the pin ends and
pulling the wires out. To install a wire, strip the wire at least half the pin
length and tin it with solder. Insert the wire in the pin and flow solder
into the end while heating it with a solder iron. A 25 watt iron should be


In the following section, the color of the wires may vary.

Power supply 9 pin connector (male):

( ) Red wire from the grey shielded cable goes to pin 7.

( ) Shield from the grey shielded cable goes to pin 4.

( ) Grey wire to pin 3.

( ) Black wire to pin 2.

( ) Red wire to pin 8.

( ) When you are finished, you should have a cable wired as follows:

9 pin/power supply 8 pin/SMS4MR

2 Black 7
3 Grey 6
4 Shield from Grey cable 2
7 Red center conductor 1
8 Red 8

If your wire colors are normal (odds are the ARE normal, but.....), this would be
the wiring color table:


Pin 8 Orange 0V Red 8 Pin 8
Pin 2 Red 22V Black 2 Pin 7
Pin 3 Red 22V Grey 3 Pin 6
Pin 7 Yellow Center Pitch Red Center 7 Pin 2
Pin 4 Shield Pitch Shield 4 Pin 1

If for any reason there is confusion about the wiring of the cable, the following table list's the Objective. The confusion may come from the fact that the wire colors change as the pass from the power supply, thru the old CMC-10 cable to the SMS4MR. In other words, regardless of the wiring of the cable, these are the connection paths that you need to make.

Transformer Red wire 22.5V------------------------------------------------SMS4 pin 6
Transformer Red wire 22.5V------------------------------------------------SMS4 pin 7
Transformer Orange wire 0V-----------------------------------------------SMS4 pin 8
Front Panel Pitch Yellow Center Conductor----------------------------SMS4 pin1
Front Panel Pitch Shield------------------------------------------------------SMS4 pin 2

The Red wired from the transformer are interchangeable.

The Front Panel Pitch Control comes in thru the 11 Pin connector with a shielded cable jumper over to the 9 pin connector ( then on to the SMS4). Also,
most M400's use a shielded cable with a Yellow center conductor from the front panel thru the power supply, but the cable between the power supply and the Motor Speed Control board uses a shielded cable with a Red center conductor.

2-7 Mounting the SMS4/MR

( ) Place the bottom of the mounting template approximately 1 inch from the
bottom of the black wood board that held the CMC board. Check the
orientation of the template (it should be inverted).

( ) Drill 4 holes as indicated on the drawing and mount the SMS4/MR with the
connectors up (on top). Use the included hardware from the kit.

2-8 Reassembly

( ) Re-install the front panel. Make sure that the track selector lines up correctly with the track selector mechanism.

( ) Replace the two wood screws securing the front panel to the cabinet.

( ) Re-connect the 11 pin connector to the power supply.

( ) Re-connect the audio plug to the power supply.

( ) Re-connect the 9 pin plug to the power supply.

( ) Connect the 8 pin connector (going to the 9 pin power supply connector) to the SMS4 8 pin connector. Refer to the component locator for the correct orientation. The notch in the board should go to pin 4 of the 8 pin

( ) Re-connect the 8 pin connector from the motor to the SMS4/MR. Pin 1(A)
should line up with the notch in the board.

( ) Re-installed the front panel PITCH control knob.

( ) Clean and de-magnetize the tach head.

( ) Check the belt tension. If necessary, loosen the two motor screws and
allow the motor to hang from the belt. Tighten the two screws. One (1") of
belt play is considered acceptable. This may require minor re-adjustment if
the belt slips. It is important that the belt is not too tight since this causes
additional and unnecessary loading of the motor.

2-9 Checkout and Alignment

( ) Re-check all connections!

( ) Set the front panel PITCH control to center.

( ) Re-connect the power cord and connect the Mellotron output to a suitable
amplifier. Set the volume to an acceptable level.

( ) Watch the motor flywheel or pulley. Turn on the power. The motor should
begin to turn.


If the motor does not turn, turn on the power and watch the flywheel or
pulley carefully. If they turn slightly and then stop, verify that the front panel
PITCH control is correctly wired. If this connection is bad, the motor will make a quick turn and stop (maybe not even a full revolution).

( ) If the motor turns correctly, allow it to run for about 5 minutes before
performing the following adjustment.

( ) Press middle-A and adjust the CENTER control on the SMS4/MR for the
correct pitch (A-440), see the attached SMS4/MR Component Locator.

( ) Reassemble the cabinet.

3-1 Troubleshooting

3-2 This section is not intended to troubleshoot a failed SMS Motor Speed Control, rather it is for troubleshooting an installation. For complete troubleshooting, refer to the Mellotron 400 Service Manual.

3-3. The following list describes some typical failures and their cause.

1. Motor makes a small turn at power on and then stops.

Cause: Front panel PITCH control not connected or control/wiring is defective.

Check: Ground pin 1 of J2 (to power supply). If the motor runs, check the PITCH
control wiring.

2. Motor runs at full speed. Front panel PITCH control may or may not have any affect.

Cause: Tach head and/or wiring is open.

Check: Measure the resistance of the wiring to the tach head. If above 50 ohms,
suspect an open tach head. Typical is about 10-20 ohms.

3. Pitch drops significantly under heavy key load.

Cause: Belt too tight or too loose.

Check: Belt tension.

4. Motor doesn't run at all.

Cause: Power supply modification incorrect.
Motor not connected.
Motor and/or wiring defective.
Main fuse blown (power lamp may still light).

Check: Review power supply modification.
All connections.
If SMS4/MR fuse blows, check belt tension (too tight) and motor.
Measure voltage between ground (heat sink screw) and the case
of the power transistor mounted to the heat sink. It should read
22V +/- 1V. Adjust 22V adjustment if necessary

5. Noise or Hum.

Some units need a wire from the SMS4 pin 8 to the ground of the power
supply chassis (metal of box). This can be done by connecting a wire form pin 8 of the power supply 9 pin connector (orange wire) to the ground lug
under the smaller capacitor, or to the chassis of the power supply.

Also, make sure that the ground wire (green or green/yellow) of the power cord is connected correctly.

4-1 Motor Wiring

In the event that motor wiring comes loose and it is not obvious where the wires belong, or it the SMS 4 is being installed in place of a CMC4, the following table describes the wire locations.

8 pin at SMS4

1 N/C
2 shield from the Tach Head Cable
3 Center conductor from the Tach Head (red)
4 N/C
5 Brown
6 Blue
7 White
8 Yellow


YELLOW BROWN (may have fuse to both)


yellow or red dot



NOTE: Tach head wires may be reversed and still work fine.



1. Take Mellotron lid, keyboard, and tape storage box metal lid off machine; put aside carefully.

2. Locate the front and rear screw strips of the tape frame. If there is a tape already in the place where the replacement tape is to be installed, perform the following steps (if there is no tape in that particular slot, perform the steps in paragraph 4.

3.a. Reel off the replacement tape until the hash mark of the replacement tape appears. This mark will eventually line up over the tape head corresponding to that tape. DO NOT CUT ON THE WHITE HASH MARK.

b. Useing scotch tape, attach the beginning of the replacement tape to the end of the tape already in the slot. Loosen the four screws holding the old tape down, and from the rear of the Mellotron, pull the old tape out, which will automatically thread the replacement tape. Be careful not to cach the splice on the tape frame screws.

c. When the white hash mark lines up above the head, tighten down the screws. Before cutting off the excess tape in front of and behind the replacement tapes, it is advisable to reassemble your Mellotron and play them . The cue mark is only
approximate and may need to be adjusted slightly.

4. If there is no tape in the slot in which the replacement tape is to be installed, perform the following steps:

a. Sit in front of the Mellotron. Remove front panel under the keyboard, exposing front of tape frame. Unwind the tape until the number and hash mark appear. Place the tape about 12” in front of the hash mark under the first set of screws on the LEFT end of the REAR strip, with the number facing up.

b. Align the hash mark between the two screws that are on the side of the head that the tape is covering (as marker for where the tape should be held).

c. With the rear of the tape in place, pull out about 60” of tape and let it fall in front of the Mellotron. The tape should be set with the hash mark over the head. The tape goes through the two tape guides on each side of the headblock.

d. Set the tape to ride over the heads through the guides and over the plastic roller connected to the tape frame. Now you must push a loop of tape down both sides of this roller (see diagram which shows this tape frame roller). Push the two loops
down until you can see them in the front panel opening (under the keyboard lip).

e. The bottom of the tape frame has springs attached to the back; the spring rides around a bottom roller and is connected to a plastic pulley. This pulley (turnbuckle)can be pulled open (pull hard).

f. Use the pulley to grab the two loops of tape and pull them down until the pulley is about 6” above the bottom of the tape frame. Now, place the tape under the front screw strips (diagram). Tighten down and cut tape about 12” past the front screw strip. NOTE: Be careful when closing pulley around tape loops not to pinch or bend the tape.


Instructions for Frame Assembly and Tape Installation for New Frame

Section l: Delivered parts (for one frame)

1. L-profile 20 x 20 x 3 mm (left) 1
2. L-profile 20 x 20 x 3 mm (right) 1
3. Top crossbar 20 x 10 mm (long) with 36 plastic separtor pins 1
4. Bottom crossbar 20 x 20 mm (short) with 36 plastic separator pins 1
5. Tape pullbar 15 x 5 mm (short) with 36 Philips screws 1
6. Tape holding crossbar 15 x 5 mm (long) with 36 Philips screws 1
7. Tape ends blocks 25 x 15 2
8. Roller axle holders 4
9. Roller axle 1.2 mm 1
10. Short tape frame thumbscrews 2
11. Long tape frame thumbscrews 2
12. Plastic rollers 35
13. Springs (European 4 cm type) with plastic turnbuckles 35
14. Plastic separators 36
15. M3 x 6 Philips screw 8
16. M3 x Philips screw 4
17. M3 nut 4
18. M4 x 10 Philips screw 2
19. M4x 20 Philips screw 6
20. M4 nut 4
21. Washer 4.3 x 10 4

You will need the following tools and things:

-- Philips screwdriver (do not use pozidrive!!) for M4 (demagnetised)
-- Philips screwdriver for M3 (demagnetised)
-- Set square
-- Combination pliers
-- Scissors
-- Stiff cardboard (or plywood) 20 x 60 cm

Section 2: Frame Assembly

Read through this whole section before you start!

1. Assembly of Basic Frame

Take a good look at the old frame that you have.
Identify the position for new parts by comparing the old frame with the different delivered parts. Note that there are no bottom rollers and no aluminum spring holder. Even though the separator holders are a bit shorter on the new frame they are oriented the same way as on the old frames. This should enable you to put together the basic tape frame.

Use item No. 1 - 4, 16, 17, 19 (four of them) and 20.
Tighten the M4 corner screws lightly Use a set square to adjust the frame to a right angle. Tighten the M3 corner screws. Check the right angle adjustment. Tighten the M4 corner screws very hard. Tighten also the M3 screws.

Use Item No. 7, 19 (the remaining two) and 21 (two of them).
Screw on the tape end blocks. Note that the screwhole in the upper crossbar is 1 mm larger then the screw. This is to allow adjustment to different Mellotron 400 versions.

Use Item No. 6, 18 and 21 (the remaining two).
Screw on the tape holding crossbar. Note that the screwhole in the tape holding crossbar is 1 mm larger than the screw. This is to allow adjustment to different Mellotron versions.

Use Item No. 8, 9, 12 and 15.
Screw on the roller holders. Be sure that they are not bent and that the holes are in a line. Put the rollers on the frame, working from one end to the other. Bend the open end of the roller axle with a pair of of powerful pliers. Be sure not to damage roller or roller holder.

2. Installing Separators and Springs with Turnbuckles

Here comes the tricky part: Putting the plastic separators and the spring with turnbuckle on the frame. They must be mounted one by one and at the same time. This is where my frame differs the most from the original frame. My springs are put on the longer side of the bottom plastic separator holder. This results in a smoothly working, shorter and straight spring that will not bend when you put the frame on the floor.

The bad part about this idea is that the springs will "flop out" of the plastic separators when you do not have any tape mounted in the frame. Therefore you should put the springs in (and the separators on) with the frame upside down (rollers down) and store the frame this way before you have put tape in it.

Put the frame upside down in front of you. The best is if you can attach it to something in a workshop so it will stay firmly in this position.
Install the separators and springs one after the other working from one side to the other.
Check how it looks like on the old frame.
Start on one side. First hand the separator on the longest of the holding points at the "upper" (roller) end of the frame.
Push the separator over to the other side so that the leash can be pulled over the other end of the holding pin. You might need to stretch the plastic a bit; a small crack won’t matter but be sure not to overstretch too much.
Pull the separator straight and stretch the separator over the longer side of the "bottom" (which is now up) holding pins.
Push the separator over to the other side so that the leash can be pulled over the other end of the holding pin. This first one does not have any spring.

Proceed with the one next to it. Before you push the separator over the longer side of the "bottom" (which is now up) holding pin you have to hang on a spring with turnbuckle. Hang the spring on the pin so that the spring body won’t be pushed against the aluminum. Push the separator over to the other side so that the leash can be pulled over the other end of the holding pin.
The first spring should now hang freely in the first "compartment". All the following separators have a spring.
Be sure to work in a comfortable poisition with a lot of table space to have the stuff on otherwise you will ruin your back/patience/tape frame/life.
Remember to store it "bottoms up" before you have tape in it.

Section 3: Installing Tapes

Read through this whole section before you start!

1. Preparation

Putting tape in an unloaded frame is another ordeal. You should have a large, clean and empty table .
You need a piece of hard cardboard or (preferably) thin plywood 60 x 20 cm.
Put the cardboard across the frame against the long separator holding pins. This is only to protect the springs from "flopping out", which, in the worst case, could damage them. Carefully turn the frame around so that it is in the same position as the frame is mounted in the Mellotron. Tilt the frame a little bit all the time so that the springs will rest firmly on the cardboard. Be sure not to push on the separators too much.
Put the frame in front of you with the rollers towards you and the frame resting on the tape end blocks and the cardboard lying on the table.
The springs should be lying neatly in their respective compartments.

2. Basic Tape Installation

Check on the old frame how the tapes are mounted. This is done the same way on the new frames.
Take out the tape roll. Check that all of the screws on the tape holding crossbar are loose and that the washers can move freely.
Key No. 1 (low G) is the one to the left. Pull out the tape until you see the marking line for the low G. The marking is on the back of the tape. The first sound (low G) starts at the mark and continues onto the reel.

With the roll to the left of you, you must cut the tape to the right of the mark so that you have 40 cm from the marking line to the end of the tape (here the type of instruments, etc. should be noted).

Push the tape under the first (left most) pair of washers with the back of the tape against the washers.
Push it under the upper crossbar and pull it out in between the first two separators. Take up the turnbuckle and push the tape in the turnbuckle the way is is on the old frame. Put the turnbuckle back between the separators and pull out some more tape. The tape should feed freely from the tape roll and between the first pair of washers and screws. Push the tape end back under the upper crossbar and put it over the roller. Pull out some more tape and put the second loop around the turnbuckle.
Pull out some more tape until the spring is completely unstretched and the start end of the tape hangs about 10 cm over the rollers, always keeping it nicely (untwisted!!) in the separator "compartment". The start end will later be secured to the tape pullbar (Item No. 5).
Tighten down the leftmost screw only (the other screw will also hold the next tape) on the tape holding crossbar.

Feed the tape from the roll, and after about 1 m you should see the next marking line. Be sure not to miss it!. Cut the tape 40 cm from the yellow or white marking the same way as above (with the roll to the left of you, you must cut the tape to the right of the mark). The free end hanging down to the floor will have to be shortened to about 30 cm from the tape holding bar. It can be shortened even more later.
Check with the old frame so that you have not twisted the tape or anything and that you are on the right track.

Proceed with the next 34 notes……
After awhile, you will get the hang of this, but it is pretty tedious. Making a mistake is no fun, I can assure you, so be very careful all the time!

When you have inserted all of the tapes yu should have 35 starting ends of tape lying on top of the rollers.
Take the pullbar (Item No. 5) and check that all the screws are loose and that the washers can move freely.
Put the pullbar on top of the separators with the washers up. Take tape No. 1 and push it under the first pair of screws with the back of the tape against the washers.
Pull it out about 4 cm. Tighten down the screw.
Proceed with the next 34 tapes.
Roll the tape around the pullbar about 4 turns to put tension on the spring. Doing this carefully and loosely there is absolutely no danger of damaging the tape. This part of the tape before the mark is never played.
The tape frame should look a lot like your old frame and you can put the pullbar end pins in the notches on the L-profiles.
Put the frame carefully in the Mellotron. Be sure that none of the turnbuckles flop out from between the plastic separators. Push them gently back if they do so and check that the tape isn’t twisted.

3. Start Point Adjustment

Unroll the pullbar and screw it in position in the back of the Mellotron.
Take a firm hold of tape end No. 1 (low G) and loosen the first two screws.
Pull the tape until the mark line is on top of tone head No. 1.
Tighten down the first screw.
Proceed withthe next 34 notes always holding on to the appropriate tape when you untie the screw.
Put on the keyboard and check all the notes.
The keyboard might need reaignment.
Cut off the tape abut 4 cm from the pullbar.

4. Tape Length Adjustment

Shortening is a matter of taste.
Many of the sounds are 7 seconds long the way they were recorded and this was the tape length that was delivered from the old Mellotron factory (or sometimes even shorter). If you accept this time limit (actually it will be around 8 seconds) you can use the following method:
-Unscrew the tape pullbar and put it back on the notches in the L-profile
-Take a firm hold of tape end No. 1 (low G) at the tape holding crossbar.
-Loosen the first two screws on the tape holding crossbar.
-Pull the tape until the spring body has been stretched about 2 cm (from 4 cm unstretched to 6 cm). This will give the spring enough tension to avoid "flopping out" during transportation.
-Cut off the tape about 3 cm from the tape holding crossbar.
If you want an even "firmer" frame you can roll the tape around the pullbar about three (3) times during transportation.

Optional Appendix - No. 1

These instructions are written for the "standard user". You might want to be a bit more accurate on the start point adjustment for example. Be sure that you have enough tape behind the pullbar to be able to adjust the startpoint accurately. Also check the adjustment of the keyboard (especially the pad and pinch roller adjusting screws) before you begin any elaborate start point adjustments. Both the pad and pinchroller affect the starting point.
If you want to be a real fanatic you can make the tape length adjustment (after the accurate start point adjustment) with the pullbar in the back of the Mellotron. You might have to push in some more tape (from the tapeholder crossbar end) to make the spring 6 cm long (if the tapes get any longer, the spring won’t pull the tape back properly). This gives you a wonderful 9 to 10 seconds (if the sounds are that long) of Mellotron sounds and a big headache when you want to transport the frame. You will have to roll the tape about 8 turns on the pullbar to avoid flopping and you will have to be very careful doing this and handling the frame this way!

Optional Appendix - No. 2

An alternate method of installing tapes in a frame that has no tapes may be found in the Mellotron video No. 2 "The Workings". This video shows the installation procedure for placing tapes in a frame mounted IN a Mellotron M400.


Headblock adjustment and head positioning.

The thought of adjusting head azimuth on a Mellotron is enough to give anyone pause. Azimuth? Ya gotta be kidding, right? Well, you know how sometimes a few selected notes are dull sounding - you've done everything,
adjusted the pressure pad overhang (more about that later), even changed the head. Still dull. Well, the problem could be azimuth, and also head "height" (I use that expression loosely, as we are talking a left-right adjustment, equivilent to head "height" on a normal tape machine).

So the trick is, how the heck do you get in there? First, isolate the note in question. (it's easier to do this with a bright sound, and easier still if you add a lot of treble to exaggerate the top end). What you need to do is take off the surrounding 4 keys (2 on each side). (Leave the key ON for the note in question). Doing this will (almost) expose the screws you need to get at to adjust azimuth and height (left-right). What you now need to do is take the closest two surrounding tapes, lift each one up and move it one position further away from the note in question. Confused? OK, let's say you're adjusting C. You take off B, B-Flat, CSharp and D. You then take the B tape, lift it up and put it on top of the B-Flat tape. You take the C-sharp tape, lift it up, and put it on top of the D tape. This clears the area for getting at the screws for the C head.

OK. Now the fun part. First make sure you have de-magnetized your screwdriver. Loosen the two screws slightly on the C head. While playing the note, use the screwdriver kind of like a "gear" to turn the head (place it slot down next to the screw, put one edge along side of the head bracket and turn). Any variations on this are OK, as long as you're careful. You will hear the top end come and go. And there will be "left-right" play, which will alter the volume - you want the track on tape to be aligned with the head (check this by slightly moving the track selector while playing - if you can make it louder by doing so, your head "height" is off). Find the point at which the top end and volume are strongest, and tighten down those screws. That ought to do it. Fun, eh?

Given by: Danny Caccavo


Adjusting the pressure pad/pinch roller assy.-  

This adjustment is the one most frequently performed in a mellotron or chamberlin. Always keep a good demagnitized screwdriver handy. My method is as follows:

First, remove the keyboard assembly and set it aside, keys down of course. Now, remove the pull bar (the tapes fasten to it in the rear of the machine) and set it in the slots povided in the front of the main tape frame assembly. Check the path the tape will take as it feeds from the tape frame into the storage box. Clean any dirty felt etc. Replace the pull bar and take off the front cover of the 'tron. See the black plastic pieces at the bottom of the tape loops? These are called turn buckles and they need to be clean as well. Use head cleaner or isopropyl alcohol and a cotton swab.

Now we are ready to put the keyboard assy. back on and adjust it. The machine needs to be warmed up a bit, turn it on for a 15 mins or so before you begin. We will first adjust the pinch roller. Why? Because if the pinchroller is in an unknown position, it has to at least get the tape moving before ANY pressure pad adjustment will have an effect. If you have adjusted the pinchroller with this procedure already, then default to adjusting the pressure pad first. The pad is the most likely component to vary in adjustment over time.The pinch roller screw is the one farthest from you in the key as you face the 'tron. The pressure pad adjustment scew (nearest you) should be backed off (counter clock wise) so no sound is heard. Now adjust the pinch roller screw until the tape starts to move in the frame. Remember, you have the front cover off now and you should be able to see this motion. Turn the p.r. screw 1 and 1/2 times past this point. Now, turn in the pressure pad screw (clock wise) until sound is heard. Not enough pressure will result in no sound or a dull, muffled sound. Too much pressure will start the tape to wow.

This whole operation requires just a little basic understanding of what is supposed to be happening and some experience. Make sure that the two rods under the pressure pads that go across the length of the keyboard are not flexed too far up or down as to interfere with the motion of the pads. Other possible bug-a-boos-

1. The pressure pad is bent or mounted off center
2. The tape frame roller is stuck or stiff.
3. The key tension nut is too loose allowing the key to not return to the top of it's travel.
4. The pinch roller may be stuck or tight. Clean, lubricate and manually "work" the roller.Remove it from the key assembly, soak it in a good head cleaner (I use Teac) and lube the roller axel with Tri-Flo or some other good quality oil. Not too much! Just one small drop will do.
5. Make sure that there is still a felt pad on the pressure pad assembly.
6. An over-stretched spring may not pull the tape back into position, replace it.

One overall point that I would like to make is this: Mellotrons and especially Chamberlins need to be played alot to work well. A long neglected instrument will get noticably better in a short time if it is played. These things are 35 tape machines in a box with many moving parts that can atrophy and stiffen when neglected.


Replacing tape frame springs.

Once again, this isn't rocket science but, you need to be very careful with this one. The springs are attached at one end to the tape turnbuckle and the other to a long "comb" of aluminum across the back of the tape frame. This comb is the part we have to handle with care. Aluminum fatiques easily. With a small flat screwdriver, carefully pry the tooth that holds the springs out a bit, replace the spring and press this tooth back in just enough to hold the spring in place.On the other end, simply re-thread the open end of the spring onto the copper hoop that attaches to the turnbuckle.


Tuning the motor speed-

The motor speed control pot is an easy item to locate on a M400 motor control board. On SMS boards, it is the middle potentiometer surface mounted to the board. On CMC 10's it is one of two pots and is always marked "speed control".

This is usually the last adjustment done when recalibrating or installing a new motor control system. Assuming that the keyboard is funtioning properly and you have a good tuner or reference pitch handy, simply set the front panel pitch knob to center and adjust the pot on the motor control board to pitch.

With old Mellotron tapes, this process is a bit of a dodge sometimes as the tapes themselves may have pitch problems. In this case, find the most "tuned to themselves" keys and adjust the overall pitch. The new Mellotron tapes made after March of '96 are well tuned and will present none of these problems.


Low Noise Modification-

Turn the power supply upside-down and place it so the heatsink is on the left.Note the two blue capacitors on the left. Loosen the mounting straps on these two capacitors and remove them.


In the following steps, some power supplies have been found to not have three wires going to the larger blue capacitor or wires that don't go to the places described. While these units are rare, DO NOT PERFORM THE LOW NOISE MODIFICATION if the wiring on your unit is not the same. Contact Mellotron Archives for further information.

The larger capacitor will have three black wires going to the negative terminal. One of these wires will go to a ground lug under this larger capacitor. Leave this wire, but disconnect the other two from the capacitor. Leave these two wires free for a moment.

The smaller of the two capacitors will have two black wires going to the negative terminal. Again, one wire will go to the same ground lug under the larger capacitor. Leave this wire and disconnect the other wire. You should now have three black wires free. Strip each end and solder all three to the ground lug under the larger capacitor.

Replace the capacitors in their respective straps and tighten the screws.

This should significantly reduce the hum and noise in the output.

I have also found that some trons develop a ground loop for no apparent reason. Chamberlins are especially fond of doing this. The cure for this in a M400 is to run a wire from the SMS heat sink or ground plane to Pin 8 of the 9 pin connector in the power supply. The only way to fix it in a Chamberlin is to fashion a constant contact tab of copper and mount it to contact the end of the capstan, then run a wire from this tab to the preamp ground. This also provides a discharge path for the annoying static pops that Chamberlins are so fond of producing. Charming.


Sticking Keys-

I have found a number of causes for this one. Each has an obvious solution.

1. The 9mm nyloc nut at the very back of the key may not be tight enough. If this is not the case, remove the stop bar (across the top of the keys) and remove the key assembly and go to number 2.

2. There is a small strip of felt glued into the hole for the keybed pins. Under the key in the front, folks. Sometimes the 20 some year old glue gives up and the felt will fold up under the key as it rides on the pin. Remove and replace with a good wood glue and new felt..

3. Very rarely the oval shaped pin will rotate and cause the thicker portion of it to ride with more friction in the keyslot. It's easily twisted back into position.

4. I found this one out the hard way: Ocassionally, if I have used a socket to adjust the key tension with the 9mm nut, the socket will actually push the key forward a bit too much making it ride too close to the pin on the keybed. It gets tight again and the usual flurry of activity insues (much grumbling, teeth gnashing etc.) Use an open box wrench or thinner walled socket.


TheTach Head- Yes, it really is mounted directly above or below the serrated "wheel" behind the motor pulley.
Locate the motor, find the pulley (hopefully under a belt). This is a standard mellotron tape head mounted with two small fasteners in a little frame. It must be clean for the motor control circuit to function properly. Any good non abrasive head cleaner will work. The head should be no more than 1/8th of an inch from the "wheel" but not close enough to touch it. Let's not saw the thing in two. Sometimes, for an unknown by me reason, this head will open up. Of course when this happens, the motor control circuit is not getting the feedback it needs to regulate the amount of voltage going to the motor. We then get a flurry of head scratching and a call to an "expert". It's easily remedied with a new head. I have litterally 10,000 of these things and give them away at any opportunity. Les Bradley once joked that I would surely be leaving something to my grandchildren.I don't have any children so you, dear reader, are welcome to them.

If you still can't find the head, try this: Tach Head Locator For The Spatially Challenged.


Things that I have found in old Mellotrons:

Mouse droppings (many times), seems that mice love the taste of Mellotron tapes, but then don't we all?

Tools. Usually flat screw drivers and vice grips.

Unusual repairs. One machine actually had the tape return springs nailed directly to the floor of the machine. NO frame.

Ladies size XXX large knickers. This one frightened me badly.

Hostess cupcake. Fossilized. Proof positive that future archaeologists will have something to judge our culture by.

The little felt doo dads that go on the pressure pad.

Kitty litter. (jeeze)

Cigarettes and their droppings.

One bag-o-dope. Not tested yet but, it could come to that.

Many set lists. One from Michael Pinder, one from Martin Kitkat, one from Rodeo Planet and 3 or 4 others.

Business cards, usually from females. One from a Yamaha sales rep. (?!?!?!?).

Lastly, I have seen many little comments written by Streetly workers on the underside of cheek blocks from 400's. Some pretty weird, some pretty funny.