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I’m looking to troubleshoot and repair which component has failed in a LED tube bulb driver. The bulb is a GE led14et8/g/4/835, and requires a ballast. These bulbs are commonly used to retrofit T8 fluorescent fixtures with LEDs.

Ideally, I’d like to either:

  1. Discover what SMD component has failed, and re-solder them myself.
  2. Bypass the embedded driver and supply 12V myself directly.

Troubleshooting:

When I plug in the bulb to a fluorescent light fixture with ballast, it emits a low hum and the LEDs output a very small amount of light. Thus, they were thrown out for a reason.

Testing individual leds inside the bulbs at 12V causes them to be overloaded. Applying 3.7V causes nice bright output.

There seems to be two drivers- one at each end, with each powering 36 LEDs. I observed no obvious shorts or burn marks.

Image of what I think is the driver / power regulator, at the end of the tube:

enter image description here

I’ve googled the model number and different variations on the issue. I’ve also googled identifiers printed on the PCB to no avail.

Conclusion: The LEDs work. I could scratch off the coating that connects the series of LEDs, solder to that and supply my own power.

Or, I could test each component, find the faulty one and replace it. However, several of the SMD components have no label on the top, and don’t seem to have colored labeling similar to resistors.

marketing pdf sheet

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  • \$\begingroup\$ “It is trash. They threw it away for a reason.” I’m here to learn about electronic circuits- and if I can fix this, I would save the $6 for a very bright LED tube- more than 1600 lumens! “Just buy a new one”. I’d rather keep this out of the landfill for a while. The led have a supposed lifespan of 50,000 hours. That is more than a hundred years. The cost of a tiny 10c smd component and some soldering practice seems worth it. \$\endgroup\$
    – CharlesW
    Sep 9, 2020 at 7:58
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    \$\begingroup\$ They won't run on 12V. The LEDs are probably connected in series, so you'll need well over 100V to light them up (36*3.7=133). The curious thing is that both sides have failed. Is there any single component that is in the current path of both sides? \$\endgroup\$
    – JRE
    Sep 9, 2020 at 8:15
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    \$\begingroup\$ Hi , there is no power regulator, it is just a series string of LED's , designed to emulate the typical 70v loaded condition of normal flouro tubes, so with about 3v per LED, you should have about 23 LEDs (or 46 depending on how they are arranged) . The middle LED on your picture seems to have a piece missing, e.g. it has "blown up" did you remove the flouro starter? I think you are supposed to. \$\endgroup\$
    – BobT
    Sep 9, 2020 at 8:18
  • \$\begingroup\$ The grey SMD parts C5 C6 are most likely ceramic capacitors maybe 1uF or similar, either to filter the DC across the LED's, or in series with the incoming supply. the smaller ones C1 C2 are just lower value 1nF? capacitors for EMI . to drive from 12v you will need to rewire the string into groups of 4. the 1k resistors (marked 102) are probably just bleed resistors , or they might go across the two pins at each end (so electronic ballasts can "see" something there). D1 and D2 are rectifier diodes, there might be another 2 at the other end. \$\endgroup\$
    – BobT
    Sep 9, 2020 at 8:23
  • \$\begingroup\$ You want to learn about what makes LED lights fail and how they work, let me then guide you to the LED guru on Youtube: BigClive: youtube.com/c/Bigclive/featured As mentioned above, this light is very likely build differently from what you think. You can only repair it if you have a detailed understanding of how it works. At this moment you do not. These lights work on high voltages (many LEDs in series) for efficiency reasons. You can de-solder the LEDs though and use them in your own contraptions. \$\endgroup\$
    – Bimpelrekkie
    Sep 9, 2020 at 8:49

1 Answer 1

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  1. The marked components to the left are resistors. "102" means 1 kiloohm. Remove them from the board and check the resistance. They look OK, though.
  2. There are two diodes, D1 and D2. Remove them from the board and test for diode function using the diode test function on a multimeter. Should show around 0.7 V in one direction, open circuit in the other. They might have failed open circuit. If they aren't marked for polarity, add a mark to them so that you get them back in the circuit with the same polarity.
  3. The unmarked gray and brown SMD parts are capacitors. Remove from the board and check for short circuits or open. You might also measure the capacitance. You have several tubes, see if the capacitors all show about the same capacitance (compare capacitors marked C1 to C1 from another light.)
  4. One LED in your photo looks different. It might be burned out. Swap in another LED from another board. Check all the LEDs for similar dark spots. Pay attention to polarity when swapping LEDs.

Do not test individual LEDs by connecting a battery directly to them. Always use a series resistor. Connecting a power source directly to an LED is a good way to destroy it.

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  • \$\begingroup\$ Given the likely topology of the circuit, the diodes could be tested in circuit, If you get ~ 0.6v then the diode is OK , if it is a short then that diode or another (nearby?) component is faulty. In all the board repairs I've done, (with in-circuit diode tests), I've never misdiagnosed a faulty diode as healthy. Now in-circuit transistor and FET tests, that's difficult to get an unambiguous test!. I once had some MOSFETs that tested 2v in one direction, and 0.6v in reverse, (punch through fault gate-drain, due lightning) \$\endgroup\$
    – BobT
    Sep 9, 2020 at 22:47

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