How To Rebuild The Vibrato Scanner

Flashing sometimes will (at least temporarily) fix a moatorboating vibrato. (See ManualZapping for some hints.)

Also note that if any of the wires leading to the scanner are broken (or connected in the wrong order) your vibrato will not sound right.

Rebuilding the Scanner

Also, please see the Hammond Technical Service Bulletin on Repair & Disassembly of Vibrato Scanners at http://www.dairiki.org/hammond/vibrato_tsb/.

Note: To rebuild the drum-type scanners attached to the motor by a belt (not mounted to the end of the motor) such as those found in the T series, see HowToRebuildTheDrumVibratoScanner.

The following was submitted by BobSchleicher to the OriginalHammondLeslieFaq.

The presence of a motorboating or chopping sound in the Vibrato can be an indication that one or more pole pieces of the Scanner have been shorted out. The likely culprit is a crystalline growth that can occur on the plated and metal composing the scanner housing (ZincDendrites). This shows up as conductive whiskers or dust between the scanner body and the poles of the scanner. High humidity and temperature is said to aggravate dendrite formation. An over-oiled scanner can also cause vibrato motorboating, though it is probably an aggravating condition to the dendrite formation. The oil coats the insulators and picks up and retains conductive dust and debris, shorting out the stators.

A Hammond technical bulletin was issued detailing corrective procedures to cure this condition. What follows is a shortened version of it:

Before you condemn the scanner, be sure the rightmost ?6AU6 is healthy. Swap with the other one to verify. If you still have the problem, measure the plate and screen voltage on V2. They should measure about 130VDC and 60VDC respectively. Plus or minus 15% is O.K. If the problem persists proceed as follows:

• Remove the two springs from the coupling to the generator. Remove the four 5/16" nuts and lockwashers at the corners of the run motor. Unsolder the seven black wires which go to the vibrato switch and the red and blue wires at the vibrato line box. Be sure to note or mark their position.
• Carefully move the motor/scanner assembly to the left and twist to move it toward back of the console.
• Remove the spring clip from the rectanglular oil trough. Lift the wick and unwind the oil threads.
• Remove the three screws which attach the scanner to the motor and separate the scanner from the motor.
• Remove the rear cover from the scanner and unsolder the wire. Be careful not to bend the pin that the two brushes contact. Raise the end brush and slide the others off.
• Make an indexing mark on the scanner by the red wire for easier reassembly.
• Remove the screws from the perimeter of the scanner and remove the cover. You will now see the stators. WATCH THAT PIN ON THE BACK!!!
• Remove all 16 screws, lockwashers, flatwashers and round insulators from the outside, the stators, and the square insulators from the inside.
• Soak everything you just removed in denatured alcohol overnight. (The original bulletin said to soak the parts in gasoline. Yikes!).
• Clean the scanner body with alcohol and a scotchbrite pad.
• Spray the clean body and dry insulators with Krylon clear. Allow to dry thoroughly. WATCH THAT PIN!!
• Make sure the rotor spins freely. If any oiling threads are missing or broken, this is the time to replace or splice them.
• Reassemble the scanner and reinstall it. Just reverse the above procedure. Aren't you glad you made those marks now and didn't bend the pin?
• When you replace the brushes, be sure to look at the bend in the brass doodads to which the springs are soldered. The lowest one goes on first.
• By the way, the problem of dendrite formation on the metal parts of the organ have been known to cause problems in other locations in which it can occur, the Vibrato and Percussion switch assemblies, etc..

Notes

You shouldn't need to, but if you want to remove the rotor from it's shaft, you'll need a BristolWrench.

Make sure you clearly mark where the red & blue wires go. Do not use a magic marker that washes off when you thouroughly clean the scanner assembly.

External References

The following is a very detailed set of instructions and photos that are extremely useful while doing your first Scanner rebuild:

(The original link is no more. The archived link is courtesy of the Internet Archive)

http://avintagesound.com/service-support.html

Here is another set of notes, based on a Hammond service note:

(The original link is no more. The archived link is courtesy of the Internet Archive)

http://www.bentonelectronics.com/vibrato.html

TopicRepair