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LED American Flag Electrical Power-up Testing

1. Connect the 24 VDC power supply plug into the barrel jack.  

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2. Apply power plugging in and turning on the 24VDC power supply.

 

3. Observe the LED flag: 

  • All LEDs should turn on

  • No flicker

  • No dim or dark sections

  • No smoke or odor

  • Let it operate for 15 minutes 

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Pass/Fail

  • Pass: LEDs are bright and stable, and nothing unusual happens

  • Fail: Any dark sections, flicker, or abnormal behavior

  • If the LED American is not fully functional, unplug and do not operate except for troubleshooting

Troubleshooting - When Nothing Lights Up

Equipment Required

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  • Multimeter / Voltmeter (set to DC volts)

 

Troubleshooting — Nothing Lights Up

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Possible Causes

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  • Power supply not plugged in or not functioning properly

  • Barrel jack not fully seated

  • Red and black wires reversed (polarity reversed)

  • LEDs installed backwards (all or most)

  • Reverse-protection diode installed backwards

  • Fuse is blown

  • Cold solder joint(s)

  • Wrong resistors values

 

How to Diagnose “Nothing Lights Up”

 

Step 1 — Check the power supply output

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  1. Set your multimeter to DC volts.

  2. With the 24 VDC power supply plugged into the barrel jack:

    • Place the black probe on the GND input pad.

    • Place the red probe on the +24V input pad.

 

Expected reading: Approximately +24 VDC

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  • If you read +24 VDC → Power supply and input wiring are correct. Proceed to Step 2.

  • If you read 0 V → The power supply is not working or the barrel jack wiring is faulty.

  • If you read -24 VDC → The polarity is reversed (power wires are backwards).

 

Step 2 — Check voltage across the fuse

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  1. Place one probe on each side of the fuse solder pads.

 

Expected readings:

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  • Good fuse: ~0 V across the fuse → Fuse is good. Proceed to Step 3.

  • Blown fuse or cold solder joint: ~24 V across the fuse (full voltage drop).

 

If the fuse is blown:

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  • There is likely a low-resistance short somewhere on the board (commonly a solder bridge).

  • Disconnect power immediately.

  • Visually inspect the entire board for solder shorts or bridges.

  • Do not reapply power until the short has been found and repaired and the fuse has been replaced.

 

Step 3 — Check the reverse-protection (Shockley) diode

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  1. Place the black probe on the diode’s positive solder joint (anode side).

  2. Place the red probe on the diode’s negative side (cathode side).

 

Expected readings:

  • Diode installed correctly and functional: ~0.3 V (forward voltage drop).

  • Diode installed backwards, defective, or a bad solder joint: ~24 V.

 

If the diode is good, proceed to Step 4.

 

Step 4 — Check voltage at any LED resistor (510 Ω)

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  1. Pick any 510 Ω resistor.

  2. Place the black probe on the GND input pad.

  3. Place the red probe on the resistor’s input side (the side closest to the edge of the board).

 

You should measure approximately +24 V.

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  1. Now measure the voltage across the resistor:

    • Keep the red probe on the input side.

    • Move the black probe to the opposite side of the resistor (output side).

 

Expected reading: 6 V or less

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  • If you measure ~24 V across the resistor → The resistor is not making proper contact (bad solder joint- open circuit) or has the wrong value.

  • If the voltage drop is 6 V or less, move the red probe to the resistor’s output side, and putting the black on GND pad).

 

You should now measure ~18 V or more at this point if the LEDs are drawing current.

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If you measure +18–24 V here but the LEDs are not lighting:

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  • One or more LEDs in that string are installed backwards or have a bad solder joint.

  • One or more LEDs in the string are defective.

Troubleshooting — One or More LED Strings Do Not Light Up

This guide applies when some LED strings work normally, but one or more strings remain completely dark (while others function correctly). Each string is independent and connected in parallel.

 

Possible Causes

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  • LED(s) installed backwards in the affected string(s)

  • One or more defective LEDs in the string

  • Poor solder joint on the resistor, or LED pads

  • Open circuit in the string (cold solder joint, poor wetting, missed soldering)

  • Incorrect resistor value installed on that string (e.g., much higher than 510 Ω)

 

Equipment Required

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  • Multimeter / Voltmeter (set to DC volts)

 

How to Diagnose Non-Functioning LED Strings

 

Preparation

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  • Power on the display with the 24 VDC supply.

  • Confirm that other strings are lighting normally. This verifies that the main power, fuse, and reverse-protection diode are working correctly.

 

Step 1 — Verify voltage at the resistor input for the bad string

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  1. Set your multimeter to DC volts.

  2. Locate the 510 Ω resistor for the non-working string.

  3. Place the black probe on the main GND input pad (any GND point on the board).

  4. Place the red probe on the input side of the 510 Ω resistor (the side closest to the edge or power rail).

 

Expected reading: Approximately +24 V

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  • If you read 0 V or very low voltage → There is a break in the power path before the resistor (trace leading to this resistor).

  • If you read +24 V → Power is reaching the resistor. Proceed to Step 2.

 

Step 2 — Measure voltage across the resistor

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  1. Keep the red probe on the resistor’s input side.

  2. Move the black probe to the resistor’s output side (the side connected to the LEDs).

 

Expected reading: 6 V or less (normal voltage drop when LEDs are drawing current)

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  • If you measure ~24 V across the resistor → The resistor is not conducting current. Possible causes:

    • Resistor not soldered properly (cold joint, poor wetting)

    • Wrong resistor value (too high resistance)

  • If the voltage drop is 6 V or less, proceed to Step 3.

 

Step 3 — Measure voltage at the LED input (after the resistor)

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  1. Place the red probe on the resistor’s output side (or the first LED’s anode pad).

  2. Keep the black probe on GND.

 

Expected reading: ~18 V or higher (depending on the number of LEDs in series)

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  • If you measure ~18–24 V but the LEDs are not lighting:

    • One or more LEDs in the string are installed backwards.

    • One or more LEDs are defective (open circuit).

    • One or more LEDs have a bad solder joint.

    • Check polarity of every LED in the string.

 

Step 4 — Visual and Polarity Check (Recommended)

 

Since there are 37 strings, systematically check the suspected string:

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  • Carefully inspect all LEDs in the non-working string for correct orientation (pay attention to the flat side / cathode marking).

  • Look for cold solder joints.

 

Additional Tips

  • Test one string at a time. Once you find the problem on one string, check the other non-working strings for the same issue (common assembly errors often affect multiple strings).

  • If many strings are out, it is more likely a systematic error (e.g., all LEDs installed backwards).

  • If only one string is affected, focus on local issues: bad solder joint, single defective LED, or reversed LED in that specific string.

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