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I am repairing my old monitor Samsung syncmaster 740b from not working CCFL lamps to LED lights with a led driver. I just had a first test. I have got electricity hit, investigation shown my metal back side of the monitor is energized.

I haven't found yet how the circuit becomes shorted on this panel. That's where I ask for your help.

Here are photos of my work so far.

a high level overview a detailed view of pins that are used by led driver part of power supply responsible for old ccfl which was turn off another side of the power supply

The part which was responsible to power ccfl has been turned off by soldering out several metal lines which connect this part of the circuit with a power line.

Led driver has four wires. Yellow ones are DIM and Enabling. Enabling I connected to the output of 12 v, DIM I connected to the output of 5 v (b-dim). Red power wire I connected to the power line at the point which previously had connection with controller of ccfl lamps. The black ground wire I soldered to a minus of the capacitor near the output.

The first part of my work where I turned off the ccfl part of a circuit shouldn't introduce new connections which might brought electricity to back panel. So I should look for an issue at the rest parts.

Update to improve questions Design: rework to LEDs reuse the same outputs ports of the power supply board to the main control board. It has four pins:

  1. Vcc - a power supply (red, 12v)
  2. Gnd - ground
  3. Enable - turn on/off the light (yellow, marked by blue electrical tape, 5v)
  4. Dim - dimmer, tune brightness (yellow, don't know the voltage)

All of them are marked by text on the board, so there is no mistake.

Steps are required by rework are:

  1. Disassemble the monitor and extract lamps. Put LEDs instead of them and assemble monitor back.
  2. Find on the power board required power voltage and ground and connect to it two wires
  3. Another two wires should be soldered to tracks which are traced to DIM and ENB ports.
  4. Optionally turn off the part of the circuit which is responsible for old CCFL lamps energizing (the second right half of the board on the first picture).

Usually you connect a power supply to an electrolyte capacitor to smooth possible spikes of electricity in the circuit. Others wires we have to put to required pins, they might be soldered directly or you could experiment with put it in somewhere on tracks which are traced from the old CCFL part of the circuit (I soldered them directly to appropriate output pins of the board). There is no a good capacitor nearby, so red power wire I connected to the power line at the point which previously had connection with controller of ccfl lamps (the last image, the circuit had several jumpers from this track to CCFL light's controller segment)

I turned off CCFL part of the circuit by soldering out jumpers.

Pairs of red&white wires go to recently replaced CCFL lamps by LEDs.

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    \$\begingroup\$ How much your LEDs require current/voltage, can the power supply provide the required current/voltage, and what do you use as power supply or LED driver for the LEDs? \$\endgroup\$
    – Justme
    Commented Mar 10 at 15:00
  • \$\begingroup\$ Some annotations and a better description of what is in the pictures would be helpful. Also detailed pictures of all the modifications that have been done to the circuit(s). \$\endgroup\$
    – DELTA12
    Commented Mar 10 at 17:57
  • \$\begingroup\$ As I mentioned in the post, the output which goes to LED is 12v, specification to the led driver with LEDs claims it is what they require. Confirmed by experience of others masters who already did such modification. Regarding photos, I did my best to record everything. At this stage I could hand mark in photos what was cut off and comments \$\endgroup\$
    – Gleichmut
    Commented Mar 10 at 18:59
  • \$\begingroup\$ maybe the ground is disconnected, or something is shorting ... the picture shows missing screws \$\endgroup\$
    – jsotola
    Commented Mar 10 at 20:10

1 Answer 1

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I solved this issue a month ago with a help more experienced electronic engineer. I did 3 mistakes here, one of those led to an issue described here.

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  • \$\begingroup\$ Good thing the issue was solved, but this does not answer what was the problem and how it was solved. \$\endgroup\$
    – Justme
    Commented May 1 at 12:56
  • \$\begingroup\$ I know, I don't remember exactly where the issue was here, so just don't want to speculate about it to avoid misleading. \$\endgroup\$
    – Gleichmut
    Commented May 1 at 13:00

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