Hammond M-2, M-3 Manual Chassis Removal
for the purpose of adding foldback
(late M3, Serial No. 147467)
By Alan DuBois © 2010 - 2016
Revised 10/28/2015
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:
Note: The number of fasteners and the location/style of some components will vary depending on the vintage or the unit you are working on.
1. Remove music rack and set aside.
2. Remove music rack base by taking out two scews in upper manual end blocks (one at each end) and carefully slide the base out and set aside.
3. Remove metal angle bar across the keys of the Upper manual by removing the two screws (one at each end) and set aside.
4. From rear, remove dust cover over tone generator by taking out seven screws from edge of generator shelf and loosening four screws in cover just below the upper manual chassis. Lay a cloth over the tone generator for protection.
5. Detach vibrato line box by first removing the harness strap for clearance (if necessary) then remove four screws in sides of box fastening it to upper manual chassis. On earlier models, remove the two screws retaining the line box to the bottom of the upper case. Carefully lay line box on top of tone generator.
6. Remove the two screws holding the Pedal drawbar control “can” and carefully detach it from the drawbar then carefully lay it on top of the tone generator. Also remove the screw and the friction clip for the “can” and set aside.
7. Desolder wires from ends of all of the drawbars. Make note of all the wire color coding & locations. DON’T LET SOLDER DROP DOWN INTO THE GENERATOR!
8. Remove the two upper manual rear stop plates (approx. ½” by 1”, one on each end) held by a single wood screw, and set aside.
9. At front of organ, from underneath, use a ½-inch wrench or socket to remove the two bolts holding the upper chassis to the case (one each side).
10. Next, remove the four screws holding the black metal cover to the bottom of the LOWER manual chassis and remove the cover to expose the terminal strip for the tone generator wiring. NOTE: The cover size and amount of screws varies with vintage of unit.
11. Also from underneath, remove three screws holding the front of Lower manual chassis to the front edge of the organ case.
12. Remove the two screws holding the left cheekblock (and percussion switches). There is an access hole in the wood frame for the outer screw; the inner cheekblock screw goes through the frame of the manual chassis. Avoid scratching any of the wood surfaces when removing the cheekblock/percussion switches.
M-3 Only: Carefully lift and then turn the percussion block/switch assembly so you can lower it back through the opening and let it hang there by the wiring. NOTE: It is suggested to support the cheekblock/percussion switch assembly in some fashion because one lead is connected to the matching transformer, which will be moved later!
Remove the two screws for the right cheekblock in like manner and set the cheekblock aside.
NOTE: Before proceeding further, you may wish to slide some protective cloth between the wood end blocks and the inside of the organ case to protect the finished wood surfaces.
13. From topside, slide the Upper manual chassis slightly rearward then prop up the front of the chassis - taking care not to damage any of the wood surfaces or the keys on either of the manuals. Block the Upper chassis in place using some small wood blocks or whatever you have available to hold the chassis in a tilted position. Don’t let it slide out the back either!!
14. At the rear of the LOWER manual chassis, use a wrench or socket to remove the two hex-head bolts holding the chassis to the case (one at each end).
NOTE REGARDING LOWER CHASSIS REMOVAL
In my experience, working on the Upper manual chassis is a lot easier if you remove the Lower manual chassis. At this point, removal of the Lower chassis only requires desoldering the wires going to the lower chassis.
If you don’t want to take the time to desolder and remove the Lower chassis, you can skip Step 15 but you must use your own method to move the Lower chassis out of your way in order to access/remove the Upper chassis.
15. Desolder all the tone generator wires from the terminal strip on the Lower manual chassis. NOTE: Desoldering may be easier if you tilt the front of the Lower manual chassis upward and block it in place taking care not to damage any wood surfaces. ALSO NOTE: The wiring loom has string loops separating each wire. If the loops are still in place, you will not need to mark each wire location. Carefully remove the Lower manual chassis from the case and set aside.
NOTE: At this point, you should consider adding foldback to the Lower manual chassis!
16. If the Lower manual chassis is removed, you can slide the Upper chassis forward and into more of a vertical position for desoldering. Note any secured wiring at the rear of the Upper chassis! Desolder the tone generator wiring from the terminal strip under the Upper manual chassis. NOTE: The wiring loom has string loops separating each wire. If the loops are still in place, you will not need to mark each wire location. Also remove the two screws and the clamp retaining the wiring harness to the left end of the Upper chassis and let the wiring harness hang. Remove your support blocks and return the Upper manual chassis to its normal position.
17. With the chassis in a horizontal position, support the control panel while detaching the six screws from the top of the control panel. Carefully let the control panel hang down, just like you did with the percussion panel, being careful not to damage any wood surfaces while also being wary of any wiring that may tug on the vibrato line box while doing so. Support the control in some manner!
18. Slide the Upper chassis toward the front of the case as far as possible, again being wary of any wiring that may tug on any loose components. Now, raise the entire Upper chassis up approximately 2- to 3-inches and support it at each end with wood blocks or whatever you have available. Be careful not to scratch any wood surfaces.
19. Remove the drawbar assembly with mounting plate by removing two screws from underneath, at front, and the three screws from top, at rear. Place a heavy protective cloth on the top of the organ case then, lift the drawbar/mounting plate assembly up and flip it over and set the drawbar/plate assembly on the top of the organ case.
20. M-3 Only: At rear of chassis, desolder the three Upper-chassis busbar wires from the terminal strip, noting the wire colors and location (Yellow-Green-White, as shown), then remove the two screws holding the terminal strip to the chassis and let it hang.
21. Remove all the playing keys. At rear of chassis, loosen all the hex-head key mounting screws at least one turn. Do not remove the screws. Lift the rear of key off the mounting screw then slide key slightly rearward and then lift out the key. NOTE: Black keys may need to be removed before removing the adjacent white keys. NOTE ALSO: It is suggested to set the keys aside in the same order as they were fitted in the chassis.
NOTE: Before continuing further, vacuum all dirt/dust from the top of the manual chassis! The next steps will expose the key contacts/busbars so, clean the chassis now to avoid any contamination.
22. At rear of chassis, just below the key mounting screws, remove the eleven or so small screws holding the rear, L-shaped cover to the top rail. (see above photo)
23. At left of chassis, remove the metal compartment cover by removing one small screw from the side and one small screw from top-left of metal rail. Set cover aside.
24. At top-rear, remove the two screws (one at each end) holding the top rail to the wood mounting blocks. NOTE: The left screw has a ½-inch hex-head nut underneath.
25. Remove the remaining twelve screws from the top rail and lift the rail out and set it on top of organ case. NOTE: The matching transformer is still attached to the rail so be careful of associated wiring and components such as the Vibrato and Percussion controls.
Also remove the narrow felt sealing strip from the chassis.
26. You should now be able to remove the upper manual chassis from the case, taking care not to damage any wood surfaces.
Install chassis in reverse order of removal noting the following:
Carefully set the Upper chassis back in the case. NOTE: The wood end blocks should be loosely fitted by the front screws.
Installing the top rail and felt seal (Step 26 & 25)
You will need an assistant to aid you when installing the top rail. The top rail is a supporting member for the chassis so, the left end of the chassis will need to be raised slightly in order to properly align the top rail when installing the rail.
With the chassis back in the organ case and supported in the raised position as you had it when it was removed, push the chassis against the right side of the case. Have your protective cloth in place to avoid scratching the finished wood surface.
Now, position the narrow felt seal across the edge of the key actuator cover as shown, with the right end tucked against the felt on the right mounting block. NOTE: This seal can easily be dislodged when installing the top rail! Be careful when installing the top rail!
Note also the position of the metal strip with threaded holes as shown above.
Finally, when you are installing the top rail, note the position of the locking tabs on the chassis and where the tabs fit into the top rail as shown.
Have your assistant support the left-rear of the chassis while you install the top rail while you also ensure that the tabs lock into place into the top rail as shown above. Make sure you don’t dislocate the felt seal while doing so!
Install the twelve small screws into the top rail. With the top rail installed properly, you should be able to see just the edge of the felt seal all the way across where it seals against the actuator cover.
Loosely fit the large screws at each end of the top rail-to-wood mounting blocks. Push the chassis to the right side of the case - to make a good seal against the felt, then final-tighten the right side screws. Then tighten the left mounting block screws.
Proceed with the reverse order of disassembly.
Tighten the screws on the bottom of the L-shaped cover (Step 22)
After installing the eleven or so small screws that hold the top-rear of the L-shaped cover to the top rail, final-tighten the five screws on the bottom of the L-shaped cover.
Continue with the reverse order of disassembly.