The operator presses a button, but the machine's actuator won't budge. Before you start disassembling expensive distributors and searching for leaks in the hydraulic system, start with the basics. Very often, the culprit behind downtime isn't the mechanics, but a "burnt" solenoid coil .
How can you be sure it's the coil that's failing, and not the power cable or valve slide itself? In this guide, we'll show you how to perform an error-free diagnosis in just 3 minutes using a standard multimeter.
Step 1: Preparing for measurement
Before testing, make sure the power to the machine (or circuit) is completely disconnected . Do not measure the coil while it is live!
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Remove the electrical plug (e.g. the popular DIN 43650 connector) from the coil.
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You will see protruding pins on the coil (usually three: two power supply pins and one ground pin, marked with the symbol PE).
Step 2: Measuring resistance
For diagnosis, we will use the resistance measurement function of the multimeter (ohmmeter).
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Set the multimeter to measure resistance ( Ohm symbol). If the meter doesn't have auto-ranging, set it to a range up to, for example, 200 Ohms or 2 kOhm.
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Touch the two multimeter probes (red and black) to the two main coil power pins (ignore the ground pin). The order of the probes does not matter.
Step 3: Interpreting the results
Now look at the gauge screen. It will tell you everything about the component's technical condition:
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A value between a dozen and several dozen ohms (e.g., 30 ohms): The coil is electrically functional! The internal wire is intact. The valve failure is likely caused by a stuck slider (dirt in the oil) or a lack of voltage at the power plug.
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A "1" result on the left side of the screen or "OL" (Open Loop/Infinity): The diagnosis is simple – the copper wire inside the coil has burned (broken). The coil is dead and will not produce a magnetic field. A new one is required.
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A reading close to zero (e.g., 0.5 Ohms): An interturn short circuit has occurred. The wire insulation inside has melted. The coil should be discarded (note: applying power to such a coil usually immediately blows the fuse in the machine).
⚠️ The Expert's Golden Rule (Why Do Coils Burn?)
You've diagnosed a burnt coil and purchased a new one. Before installing it, remember the most important rule of plumbers:
Never connect power to a coil that is removed from the valve stem!
A coil without a steel core inside it loses its inductance. If you apply voltage (especially 230V AC) to it while holding it dry, a huge inrush current will flow through it. The coil will become red-hot and burn out in mere seconds. Always slide the coil onto the valve first, tighten the nut, and only then connect the plug.
Summary
Diagnosing the coil with a multimeter is the quickest way to save time and money. If your test indicates an open circuit, you don't have to replace the entire distributor.
Just purchase the coil. Check out our range of replacements for NG6 , NG10 , and other standards: Electromagnetic coils at BRhydraulic Remember to select the appropriate voltage (12V, 24V or 230V)!