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

Hammond M3 Foldback Instructions

Revised 10/2016

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

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

If your have any uestions, 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), Nevr-Dul Magic Wadding Polish, alcohol, swabs and an ohmmeter.

Some helpful tools

M3 Upper manual chassis on the bench (after my suggested removal method)

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 actuator 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 will now have clear view/access to the key contacts.

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(s) 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, short busbars with three full-length busbars and add all the "missing" key contacts.

Further explanation regarding the upper manual and units with percussion

Depending on the model spinet organ you have, either the 6th or the 8th harmonic busbar will have all the key contacts in place for that busbar. Why are the contacts already in place? Answer: Spinets with Percussion had to have these contacts going to Ground (either at the 8th or 6th busbar) so that percussion will work all the way up the manual.

This documentation describes adding foldback to an early M3 so, in this description, Notes 44-61 should have contacts in place for the 8th harmonic busbar and all these contacts are Grounded. Other/later spinets may have contacts in place for the 6th harmonic busbar with contacts for Notes 49-61 going to Ground.

Finally, you will probably find some blank or "dummy" contacts at the upper end of the manual. 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 for wire color and location.)

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.

We'll start by removing the top contacts for keys 44-61. Count from the left, 61 down to 44. (Lower chassis is keys 37-49.)

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

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!

1Using a needle-nosed pliers, slightly bend the No. 44 key contact to the left to unlock it and then pull the contact straight out. Just let the contact "dangle" for the moment and continue to the left, completely removing all the top contacts from keys 44-61. (Upper chassis only! On the Lower chassis, slide the contacts back only far enough to remove locks from notes 37-49.)

2As explained previously, the topmost contacts for notes 44-61 are there only to make the Percussion work all the way up the keyboard. Rather than mess with that loom of wiring in order to remove/relocate those upper contacts, snip the contact wires where they enter the loom and toss all the contacts. (Upper Chassis Only!)

Believe me, you don't want to get into that wiring loom especially since most of the wires are glued together. Not with actual glue but, probably with a sugar and water mix (for all I know). Even though the wiring can be separated, why spend all the time getting those wires out of that maze of wiring? Just cut the contacts out and toss 'em (or use them for Christmas Tree ornaments).

With the top contacts removed (or pulled back), you will now see the tops of the bakelite locks that lock the actuators in each stack. We need to remove the locks for notes 44-61. (On the Lower chassis, slide the contacts back only far enough to remove locks from notes 37-49.)

3Use your pliers to pull all the locks straight up and out. Set all the locks aside.

4Now remove any and all of the blank/dummy contacts that you may find near the upper (left) end of the manual (contacts with no wire connections) and toss 'em.

5Turn 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.

6At the left end you will see the Ground terminal where the 18 contact wires from notes 44-61 are connected. We already snipped out those 18 contacts so, just snip the wires at the Ground terminal. Then, snip these same wires back an inch or so away from the terminal strip and then forget about them. Also, snip off that short, black ground wire with the ring terminal – it’s no longer needed. (Upper Chassis Only)

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

BUSBAR REPLACEMENT

Upper ManualLower 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 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:

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.

1Position 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.

2Start 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.

3With 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!

4Now, 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.

If you find any anomolies for frequencies 79 and lower, then you have a problem that existed before you did the foldback procedure. OR, you damaged something during the process. You will need to find the problem and fix it.

If the offending frequency/key is not related to a contact you installed, first doublecheck your ohmmeter connections and retest. If you still don’t have continuity, you can:

1) Resolder the terminal you are checking - just in case it has a bad solder joint or

2) Remove the offending contact and snip the contact wire, then replace the contact with one of the extra contacts included in this kit and solder the lead to the proper frequency terminal on the the strip.

If the offending frequency/key is related to a contact you installed, first doublecheck your ohmmeter connections and retest. If you still don’t have continuity, refer to the Upper Manual Frequency Chart to locate the offending contact and do a visual inspection to determine the cause.