TOOLS NEEDED: Needlenosed Pliers, Dental Picks, Desoldering Tool, Solder, Soldering Iron/Gun

Hammond M2 Foldback Instructions

Revised 01/2016

This documentation is to accompany the foldback kits I have available on eBay.

To find my kits, search for “Hammond Foldback” on eBay.

If you have any questions, contact me at:

The procedure described herein is for the Upper Manual Chassis and is performed with the chassis removed from the organ, “on the bench.”

Some tools needed for benchwork: Flat-blade screwdriver, needle-nosed pliers, small picks, desoldering tool, solder, soldering iron/gun, screwstarter (optional), one can of Nevr-Dul Magic Wadding Polish, alcohol & swabs and a ohmmeter.

Some helpful tools

M3 Upper manual chassis on the bench

WARNING! Beware of any sharp, metal edges on the manual chassis assembly! You can easily injure yourself while handling the chassis.

Remove the left and right wood mounting blocks and set aside. Note that the right wood block has felt attached to it which seals the compartment containing the busbars and key contacts.

Rotate the chassis end-to-end and then turn it over and, from the bottom of the chassis, remove the five screws from the L-shaped compartment cover. (NOTE: The five screws are already removed in this photo)

When removing the L-shaped cover, push (or pull) the busbar wiring through the hole in the L-shaped cover - then set the cover aside.

Also remove the paper insulator from the bottom of the compartment and set aside.

Remove the 11 screws holding the cover over the key actuators. Remove the cover and set aside.

Also note the felt sealing strip below the actuator cover and set it aside as well.

If present, slide out the threaded metal strip that the top rail secures to and set it aside.

You should now have clear view/access to the key contacts from top and rear.

Some history and explanation - based on my knowledge

When Hammond introduced the spinets, cost-cutting measures were incorporated. Compared to consoles - which used full-length busbars and nine contacts for all keys, the Spinets have three (sometimes four) shorter busbars AND, some of the key contacts were eliminated at the upper end of the manuals. So, there was no folding-back (repeating) of harmonics - compared to the console organs.

What we are going to do here is replace the three (or four) short busbars with three (or four) full-length busbars and add all the "missing" key contacts.

You will probably find some blank or "dummy" contacts at the upper end of the manuals. Why are they there? My best guess is to provide resistance so the player would not notice any difference in the action due to missing contacts.

NOTE: To ease installation of the key contacts, I strongly suggest that you remove the busbars prior to installing the contacts. If you do remove the busbars, make sure you note each of the busbars’ wiring color and location! (See BUSBAR REPLACEMENT below in this document.)

In the Frequency Chart, the colors and Harmonic references are NOT in the order of the drawbars! The wire color represents the busbar location in the chassis. If you didn’t note the colors, they are shown in the photos later in this document.

Working with contacts (Upper chassis)

Note: We will be working at the back and bottom of the manual so the terminals and key/note numbering will be high to low - as in left to right, facing from the rear.

ALSO NOTE: The key numbering is based on the consoles – which have 5 octaves and 61 keys. Since the spinets have only 44 keys, the first key is No. 18 and the high C key is No. 61 On the Lower manual, the first key is No. 6 and the high C key is No. 49.

First, we have to remove the key actuator locks from each stack of contacts. We'll start by sliding back the top contacts for notes 44-61 (Count from the left, 61 down to 44).

Note: The above photo was taken post-operation - the narrow metal strip at the rear should already have been removed.

NOTE: A small wood block comes in handy to tilt the chassis while doing your work and also so you don’t lay the chassis on the actuators and possibly break them!

1 Using a needle-nosed pliers, slightly bend the No. 44 key contact to the left to unlock it and then pull the contact straight out – but only far enough to expose the bakelite lock.

With the top contact pulled back, you will see the top of the bakelite lock that locks the key actuator in each stack. Continue to the left, sliding back all the top contacts just enough to remove locks for notes 44-61. (37-49 on the Lower manual)

2 Use your pliers to pull all the locks straight up and out. Set all the locks aside.

3 Before continuing, you must push the top contacts for Notes 44-61 back in through the guide plate, key actuator and into the busbar channel. Wiggle the key actuator or your angled pick to bend the tip down slightly as you push the busbar back in until it locks. This is to keep those contacts in place while you do your foldback work;

4 Now remove any and all of the blank/dummy contacts that you may find near the upper end of the manual (contacts with no wire connections) and toss 'em. Be careful not to damage any adjacent contacts/wiring when you remove the dummy contacts!

5 Turn the chassis over and support it at the topside with a wood block. NOTE: I used a Sharpie marker to mark the chassis for frequencies 80-91. Or, should I say 91-80. Remember, we’re looking at the back of the chassis.

After marking terminals 91-80, I suggest marking the terminal contacts in groups of, say, ten. e.g.: 70, 60, 50, etc. all the way across the chassis. You’ll see why I suggest this when you get to the section “Check Your Work.”

This photo is from an M-3. There is no Ground terminal at the left end on an M-2!

There are two methods to installing the contacts:

a) You can install the all the contacts for one busbar at a time, starting with the lowest busbar in the stack or,

b) Install by frequency, starting with frequency No. 80.

I chose the second method which is described herein.

6 Desolder frequency terminal 80 leaving the existing wires looped around the terminal.

7 Get seven “new” contacts ready. Avoid touching the tips of the contacts! Loop the seven contact wires around terminal No. 80. Use your pick to aid your work. As you loop each wire over the terminal, drape the wiring and contact straight up and over the chassis out of the way.

I will send you this page after you have purchased the kit.

BUSBAR REPLACEMENT

Upper Manual Lower Manual

Loosen the two, slotted, brass screws approx. 1 turn. Do not remove the screws. Now, slide the busbar retainer to the left and then slightly tighten the screws to hold the retainer in place.

WARNING: Be very careful when removing/installing and/or handling the busbars! Do not bow or otherwise bend any of the busbars! Also, make note of wire color and location!

The busbar wiring will most likely be tied in a single knot. Separate the wiring. Use your pick if need be to undo the knot. Carefully slide out the busbars, one at a time, and lay them on a clean, flat surface in the same order as you remove them, preferrably top-to-bottom.

BEFORE CONTINUING: If you haven’t performed Foldback yet, go back to “Working with contacts” near the beginning of this documentation.

With all the busbars removed, you will see that three (or four) of the busbars are shorter in length. Make note of the wire color and the location of each of the shorter busbars that you have removed.

Work with one busbar at a time.

Desolder the wire from the old, short busbar.

Solder the wire you removed from the old short busbar to the new long busbar.

Now it’s time to clean the busbars. Below is the URL to a HammondWiki regarding busbar cleaning:

http://www.dairiki.org/HammondWiki/BusbarLubeJob

BE VERY CAREFUL WHEN CLEANING THE BUSBARS! DO NOT BEND THEM!

NOTE: If you are certain that you have installed all the contacts correctly, then put all the locks for 44-61 back in now – before you reinstall the busbars. If unsure, skip the next two paragraphs and put the locks in later.

Place the manual chassis flat on the bench, bottom side down and the rear toward you.

As described previously, use a needle-nosed pliers and slightly bend the contacts to the left to unlock them and then pull the contact straight out but, this time, we only need to pull them out far enough to clear the actuators and the slots for the locks.

With the top contact slid back, hold the actuator toward you - either with your finger or the angled pick, so there is room for you to insert the lock. Reinsert all the locks then go back and carefully push all of the top contacts back into place just as you did when performing foldback.

Installing the Busbars

After cleaning, reinstall the busbars, one at a time, starting with the lowest busbar in the stack. Refer to the wire colors you recorded previously.

Install the busbars slowly and carefully. If you meet resistance, make repeated tries using light force. That failing, you can slightly twist the busbar and/or slightly bow the busbar while making repeated light force to aid in installing it.

If that fails, then use your angled pick to align the end of the busbar through each of the busbar guides until the busbar is fully installed.

Once all the busbars are in place, loosen the two screws on the busbar retainer and slide the retainer back over the ends of the busbars and then tighten the retainer screws.

Finally, and this is optional, use the busbar shifter (large slotted brass screw) to move the busbars all the way to the left. Then, turn the shifter screw in the opposite direction until the busbars just start to move to the right then turn the shifter screw one additional turn.

CHECK YOUR WORK!

NOTE: Before continuing, you must reinstall the busbars.

To make sure your work is error free, grab your ohmmeter and do the following checks while referring to the Upper Manual Frequency Chart.

NOTE: When I originally compiled these docs, I explained how to test for the “new” contacts installed. I now feel it necessary to check ALL the contacts/busbars based on my own experience, as follows.

Reason is, I did a foldback procedure on a chassis that I was selling so, I decided to check ALL the contacts for continuity. I found ONE note that had no continuity for frequency No. 54. Yet, I had done nothing affecting the contacts for frequency No. 54! So, it became obvious to me that the note wasn’t working BEFORE I did the foldback operation! It probably didn’t work from the factory – but no one noticed!

If you find this anomoly, it could just be a bad solder joint at the terminal strip. Rather than taking the time to track down the problem, I just pulled out the contact for the key/frequency that wasn’t working and snipped the lead back to where it enters the loom. I then installed a “new” contact and soldered the lead to the corresponding frequency terminal. Problem fixed. I’ve included extra contacts with this kit should you happen upon this situation.

Based on this experience, I suggest checking ALL the notes/busbars/frequencies as described below. It takes some time to check everything but, you don’t want to put the whole thing back together - and back into the organ, just to find that one or more notes may not play a frequency!

You will be checking for continuity for each busbar, through the key contacts, to the frequency at the terminal strip by pressing on the key actuators for every key/note the frequency should be impressed on.

To begin, one of your ohmmeter leads should have an “alligator” or similar clip to connect to the busbar wire leads. Your other ohmmeter lead should have a very sharp-tipped probe to ensure a good contact at the terminal strip.

The following uses Upper chassis numbering.

1 Position the manual chassis where you can access both the terminal strip on the bottom and also be able to access the key actuators on the top.

2 Start by connecting the ohmmeter lead with the alligator clip to the BROWN busbar wire - the first busbar as shown in the Upper Manual Frequency Chart.

3 With the sharp-pointed ohmmeter lead, probe the first terminal on the chassis terminal strip. This is frequency No. 18. You should NOT have continuity until you press the actuator. Now, lightly press down the actuator for the first key (Key No. 18 and frequency No. 18). You SHOULD have continuity.

If you don’t have continuity when depressing a key actuator while checking the corresponding terminal on the terminal strip, then you have a problem! If you DO have continuity without depressing the key actuator, you also have a problem!

4 Now, move the sharp-pointed lead to the next terminal on the strip and then lightly press down on the next key actuator. Repeat this process for each successive key and corresponding terminal all the way up the keyboard for the same busbar.

When you get to the keys and frequencies the you have added foldback to, you will have to “foldback” your sharp-pointed ohmmeter lead back down to the correct frequency on the terminal strip while checking the rest of the key actuators. e.g.: When checking the Green busbar lead for the “C” key (No. 61), move the ohmmeter lead back to frequency No. 80 on the terminal strip.