Lost password?

Console Start and Run Switch Wiring

General Description

From Service Manual

When the organ is started, the starting switch is turned on and held for about “8” seconds while the starting motor brings the system up to speed. The “run” switch is then turned on. This switch simultaneously connects the synchronous motor and introduces a resistor in series with the starting motor (Figure 1), thus reducing it’s driving power. With a braking action of the synchronous motor and a loss of power of the starting motor, the system slows to synchronous speed and the synchronous motor begins to carry the load.

Figure 1 - Switch and Motor Circuits

Figure 1 – Switch and Motor Circuits

This has always been more confusing than it should be. This run switch has an extra pair of contacts that are connected to the start switch resistor.

When the run switch is off, one pair of normally closed contacts simply short out a series resistor with the start motor. This allows the start motor to have full power when it is used to first start up. After the run switch is turned on, those contacts open causing the series resistor to be introduced to the start motor reducing it’s power. Also, the run motor is powered up with the other set of normally open contacts.

Here’s Another Look At The Run Switch Wiring:

Figure 2 - Run Switches

Figure 2 – Run Switches

Start Switch On

Above shows the current flow with the start switch on and the run switch off, just as when starting the organ

Start and Run Switch On

Heres the current flow with both switches on. Notice the current now goes through the series resistor of the start motor. This reduces the start motors power as the synchronous motor is taking over.

Run Switch On

Now the run motor is on and the start is off

So can a Hammond not start because of a bad run switch? You bet! The series resistor must be shorted for the start motor to have enough power to start the generator. If you have a starting problem here’s a test;

Figure 4 - Line Panel

Figure 4 – Line Panel

Looking at the above diagram, you see the large wire wound resistor which is located on the line panel on the generator. This is a 250 Ohm 10 Watt resistor. On models with two generators, this would be a 125 Ohm. If you suspect the run switch contacts which short out the series resistor for the starting motor, you can short this resistor out yourself with a clip lead and then try the start switch. If the run switch contacts are bad, then you will now see more starting power. In this case, replace the run switch.

If there is no difference then you may have a bad start switch.

Always remove the power cord from any power source when changing out any switches or modifying any wiring. This is all connected to 117 Vac and is lethal.

It is also common for older consoles to have brittle insulation on certain wires which should be replaced for safety.


This information is for educational purposes only and no claims are made that this information will lead to any successful repair. Benton Electronics assumes no responsibility to its use.

Service Manual – The Hammond Vibrato Hammond Generator Start Motor
Service Manual – The Hammond Vibrato
Hammond Generator Start Motor

Comments to “Console Start and Run Switch Wiring”

  1. thanks, bad run switch was causing a slow start motor for me, shorted the resistor and it ran up to speed. New run switch now and all is good.