LCD Monitor with LED Backlighting and Linear Power Supply Tutorial

by Eli,


Today's electronic devices are making people ill and impairing them with an ailment called Electromagnetic Hypersensitivity (EHS). The impairment can become so severe such that using a computer is too painful. It is the goal of this tutorial to describe how to modify a standard LCD monitor to make it more tolerable. Primary modifications include:


Main Components of the Monitor

  1. LCD monitor

  2. Remote linear power supply in shielded case

  3. Power supply extension cable

  4. Connector for power supply extension cable

  5. Shielded AC cord for the remote power supply

This picture shows the main components of the LCD monitor. At the rear of the monitor is the connection receptacle for the remote power supply. Note that the “IP board” or switching power supply has been gutted from the chassis of the monitor and replaced with the remote power supply. The AC power chord no longer connects directly to the monitor, but rather connects to the remote power supply. The components include:

    Parts List


MFR Part #

Vendor Part #


LCD Monitor

Samsung 731BF



Lumileds Lighting


Future Electronics, inc


Heat Sink


Digi-Key NZ-5533


Silicon Grease


Digi-Key NZ-263


Crimp Pin Contact (Male)

02-06-2103 (Molex)

NewarkInOne 35C4909


Crimp Socket Contact (Female)

02-06-1103 (Molex)

NewarkInOne 35C4908


12 Contact Connector -(Female)

19-09-1126 (Molex)

NewarkInOne 83C8069


12 Contact Connector (Male)

19-09-2126 (Molex)

NewarkInone 22C6724


Bridge Rectifier

International Rectifier


NewarkInone 06F8797


Voltage Regulator

National Semiconductor


NewarkInone 07B6484


PCB Prototyping Board

Vector Electronics



Toroidal Power Transformer 50VA

Hammond 182N6

NewarkInone 95B5026

1 or 2


Transformer Kit

1 or 2

Hook-up wire (AWG 18)

Dearborn 171819-100-9

NewarkInone 03F4432

1 (100 ft)

Hook-up wire (AWG 20)

Electrolytic Capacitor (4700 uF)

Multicomp MCHT472MICB-1633-RH

NewarkInone 79K3628


Electrolytic Capacitor (47uF)

CDE Mallory SKA470M035

NewarkInOne 16F2302


AC Power Cable

Radio Shack

LCD Monitor Service Manual (731BF, 931BF)

Mu metal (0.006” thick – 15” x ?)

Ad-Vance Magnetics, Inc

AD-MU-80 Foil

Resistor (1.8 Ohm)


NewarkInOne 94C2294


Resistors (½ Watts – 120, 330, 39 ohm)

Installing LEDs

LEDs Installed in Upper Part of Monitor

  1. 20 AWG wire

  2. LEDs

    After the fluorescent tubes are removed, the LEDs can be added. A total of 8 LEDs are installed, 4 on top, 4 on the bottom. The above picture shows the top 4 LEDs. The LEDs are all wired in parallel. Each is glued to the metal chassis of the monitor. The metal chassis serves two purposes; to hold the LEDs securely in place, and to serve as a heat sink. The LEDs are simply glued to the chassis with crazy glue.

LED Schematic

Power Supply

Expanded View of the Power Supplies.

  1. Mu metal case

  2. Toroid Transformer

  3. 5 volt LCD power supply

  4. 700 mA LED power supply

  5. 12 volt fan

  6. AC Power chord

  7. 12 volt cable for fan

  8. 18 ft cable from power supply to monitor

The power supply comprises a linear 5 volt regulated supply to power the main board of the LCD, and a 700 milli amp linear current regulated supply for the LEDs. A single toroidal transformer has two secondary windings, one for each power supply. If one is willing to pay the extra price, two independent 50 VA transformers was found to reduce the emitted magnetic field. An external 12 volt linear power supply is used to power the fan.

Each power supply is wrapped in a few layers of 0.006” mu metal foil to reduce the magnetic field. The transformer is placed on a towel to keep it centered in the mu metal case. Don't let the transformer come in contact with the shielding – keep some distance. The case is made of 0.06” thick mu metal shielding which was bought in bulk quantities at a hefty cost. One may want to use the 0.006” and wrap it into a few layers. The heavier the shielding, the less emitted magnetic field.

    Close up View of LED power supply

  1. Rectifier

  2. Capacitor (power conditioning)

  3. Linear Voltage Regulator attached to heat sink

  4. Resistor

  5. Capacitor (output stabilization)

  6. PCB Prototyping Board

The electronic components are soldered into a PCB prototyping board. Connections are made with 18 AWG wire.

    Schematic LCD 5 Volt Power Supply

    1. T1 – 50 VA Toroidal Power Transformer

    2. R1 – Rectifier

    3. C1 – 4700 uF Capacitor

    4. C2 – 4700 uF Capacitor

    5. C3 – 4700 uF Capacitor

    6. C4 – 47 uF Capacitor

    7. R1 – 120 Ohm

    8. R2 – 369 Ohm (39 + 330)

Schematic LED 700 mA Current Regulated Power Supply

  1. T1 – Toroidal Power Transformers

  2. R1 – Rectifier

  3. C1 – 4700 uF Capacitor

  4. C2 – 4700 uF Capacitor

  5. C3 – 4700 uF Capacitor

  6. C4 – 47 uF Capacitor

  7. R1 – 1.8 Ohm


Making the Power Cable

Insulated Power Cable

  1. Aluminum Foil

  2. 18 AWG Wire

  3. Bare, grounded wire

Insulated, multi-core cables are very expensive so it pays to take the time to make one yourself. Lay the wires out (18 ft in this case), including a bare (uninsulated) wire which is used to ground the aluminum shield. The grounded wire is then connected to a ground source. Add the Molex connectors to both ends.

Monitor Main Board Power Supply Filter

This filter goes between the DC linear power supply and the monitor. It's placed as close to the monitor controller board as possible. It's vital function is to prevent noise emitted from the LCD main board from being conducted onto the power cable. This filter reduces the 60 Hz and 30 kHz noise.