Low Voltage Transformer Troubleshooting (2023)

Check Power To Transformer

If the transformer uses a photocell, timer, switch.
Photo cell, timer, switch failure is a common cause of transformer malfunction.
You should have an option to turn the transformer on manually. For now select manual operation, which means not to use photo cell or timer.
If no photocell, timer or switches;
Verify AC power to primary winding of transformer (primary winding is where plug wires connect to transformer), then go to step two.
This means you need to open up the cover, access the wire that feeds the transformer.
Note: At any time along the way, if you are apprehensive, a new transformer is the way to go. You get better design, clean contacts, and save time.
Verify that the Photocell, Timer, Switch Operate Properly

What we are looking for is switches in the circuit pass AC power to the primary winding of the transformer when they are supposed to.

If you do not have a photocell but switch or timer, wiring will be nearly the same. You will be looking to see AC power to the primary winding of the transformer.

1. See if power is to the photocell. Check the wiring to and from from the photocell. Most transformers in place today get power to the primary winding through the photocell. This will be 120v AC.
2. 2 wires attached to the photocell are power in and power out. The third wire is the ground. Disconnect the wires. Remove it for testing. Pay attention to condition of wires.
3. Cover over the lens on the photocell with black tape. Photo cell lens Must be dark. A photocell is a light sensitive switch, and can take seconds to minutes to switch on.
4. A multimeter can be used to ohm out the two power wires. The power wires will show no resistance when the photocell lens is taped over. The power wires will show High resistance when the photocell lens is NOT taped over.
5. If the photocell is exposed to enough light at night, street lights etc. The black tape will reveal this.

If you are not able to ohm the circuit, You can jumper the power supply around the switches.

Transformers can also use a fuse and or a reset (circuit breaker) switch.
You can open any transformer and measure where voltage is or is not; and debug the circuit. All most never will the coils (the heavy part you can't fix) be the problem. In wet conditions with older installs, you may be better off buying a new transformer.

A Non Contact Tester saves lots of time.
You will still need a multimeter To accurately measure voltage, or ohm out a circuit, like a photocell.

Verify AC power to the primary winding of the transformer before moving to step 2.

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Check Power Out From Transformer
If you have power to the transformer

1. Verify power on the secondary side of the transformer. Looking for 12+ DC volts here.
2. Use a voltage tester and check for power on the landscape wire. 12 - 15 volts DC is typical and what to look for.

If power is not detected on the landscape wire;

• Open the transformer for access to where the landscape wire is attached to the transformer output terminals.
• Check the connections. Check where the landscape wire connects to the transformer. Make sure the wire is strong and clean. If connections are old and or feeble, disconnect the landscape wire, cut off to wire looks new. Then strip enough to make a strong connection and re connect.
• Check for power anywhere on the secondary side of the transformer. This will be where wires from the transformer are connected to the output block where the landscape wire connects. You want to check for voltage at the transformer itself. Not farther down a wire. Could be a broken connection here.

If you DO NOT HAVE power at the secondary side of the transformer;

• Look for a Reset Switch or Circuit Breaker
• Look for a Fuse

If you still cannot detect power on the secondary side of the transformer, consider a new transformer.

If you consider a new modern transformer;

Also consider it is a good time to switch to LEDs. Most older fixtures can be equipped with retrofit LED bulbs. 1/5th wattage over halogen. There is an LED retrofit for almost all popular fixture and bulb types.

If you have power out the secondary side of the transformer, follow wires to the wire tap block.
When the wire tap block gets 12+ DC volts, we know the transformer works.

Verify DC power to the secondary side of the transformer before moving to step 3.

Newer Transformers like the one below might pay for themselves in the long run. Prices are right, parts are available. Usually just the photocell. The Malibu, replacement parts (photocells) are available. This model the photocell just plugs in. Another feature with this model transformer, the photocell is on a long cord. This allows the option mounting the transformer in locations where an attached photocell would not provide the desired results for dusk and dawn. The photocell on a cord, allows better placement for light detection.

Malibu 120 Watt Power Pack with Sensor and Weather Shield for Low Voltage Landscape Lighting Spotlight Outdoor Transformer 120V Input 12V Output 8100-9120-01

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If you DO HAVE DC POWER on the secondary side of the transformer and no power to the landscape wire;

• Circuit to landscape wire connection block may be fused.
• Check wiring from secondary to landscape wire block.
• Some higher end transformers feature timer and photocell on secondary side multi tap. Check the Photo Cell is working, may be fused also.

When DC 12+ volts is verified on the output block and wire, check for voltage at the nearest light. Keep in mind bulbs and fixtures fail. Most common problem is poor wire connections.

Verify DC power on the output block and wire before moving to step 4.

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STEP 4