E-Series OSMAC: OEM 8-Station Output Board Keeps Blowing the 3-AMP Fuse

LESSON SUMMARY: This lesson is designed to assist the user in troubleshooting what would cause the 3-AMP fuse on an 8-Station Output Board to blow.

Special Tools Needed: Digital Multimeter, Phillips Screwdriver

CAUTION: THIS LESSON MAY INCLUDE INSTRUCTIONS TO TEST HAZARDOUS VOLTAGES (120V-240V) THAT CAN CAUSE SERIOUS INJURY OR DEATH. IT IS RECOMMENDED THAT A LICENSED ELECTRICIAN BE CONTRACTED TO PERFORM SUCH TESTS.

🛑 STOP: ALWAYS TURN OFF THE POWER TO THE SATELLITE BEFORE REMOVING OR INSTALLING ELECTRONIC COMPONENTS.


If the 3-Amp Fuse on an E-OSMAC 8-Station Output Board continually blows, there is likely a shorted solenoid connected to one of the eight stations that the corresponding output board controls. A shorted solenoid is a solenoid that has sustained damage, causing the solenoid to draw an excessive amount of current from the satellite’s power source. This drawing of excess current will cause the 3-Amp Fuse on the 8-Station Output Board to blow. The fuse will continue to blow until the short is identified, disconnected and resolved.

It is also possible for a shorted or damaged 16-Station Switch & Surge Board to cause the 3-Amp Fuse on the 8-Station Output Board to blow. 

Testing Solenoid Resistance:

*Note: The following steps should be completed without powering off the satellite.

To start, check the resistance of the solenoid(s) connected to the 16-Station Switch & Surge Board.

Begin by switching all switches on the 16-Station Switch & Surge Board to the OFF position.

Next, using a digital multimeter on the OHM setting, place one probe of the multimeter on the Valve Common (located at the bottom of the Pump Common Board in the far left of the satellite), while using the second probe to measure each individual station output on the 16-Station Switch & Surge Board.

To measure each individual station output, hold the second probe of the multimeter on the screw containing the station wire. (See picture below)

Proper OHM readings are as follows:

In-depth instructions on how to check solenoid resistance can be found here.

If you do not find an individual output that measures significantly outside of the above listed ranges, proceed to test the 16-Station Switch & Surge Board.

Testing the 16-Station Switch & Surge Board:

Start by powering off the satellite using the On/Off rocker switch located on the front of the Power Supply Assembly.

Using a Phillips screwdriver, unscrew the mounting screws used to hold the 16-Station Switch & Surge Board in place.

After removing the mounting screws, use a Phillips screwdriver to unscrew and release the station wires from the screw terminal located at the base of the 16-Station Switch & Surge Board.

Unplug the 16-Station Switch & Surge Board from the 8-Station Output Boards and remove the 16-Station Switch & Surge Board from the satellite.

Proceed to install a new or known-working 16-Station Switch & Surge Board where the previous unit was removed, reconnecting all station wires and plugging the new 16-Station Switch & Surge Board back into the 8-Station Output Boards.

Power the satellite back on.

If replacing the 16-Station Switch & Surge Board with a known-working unit resolves the issue, the original 16-Station Switch & Surge Board is damaged and should be replaced.

Replacement 16-Station Switch & Surge Boards can be purchased here.


Lesson tags: toro, eosmac, toro eosmac, e series osmac, eosmac repair, eosmac help, eosmac troubleshooting, eosmac exchange, eosmac motherboard, eosmac output board, eosmac switch surge, solenoid resistance, boardtronics

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