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I have a number of 4 ft (1200 mm) linear LED assemblies which were replacements for fluorescent tubes. (Ballasts were removed).

Three-four of these (~10%) have started to fail after 1-2 years of infrequent use. I'd like to troubleshoot this if possible.

The failure starts as with constant flickering, and this lasts for months. Eventually however the light dies completely.

In all cases the other LED tube in the same fixture continued to work. So its not the fixture.

I've posted photos of the driver board carefully extracted from the assembly. If its possible to test & identify a bad component I'd like to try that, both out of interest & possible economy.

If testing is needed I Can perform a comparison to an identical working unit.

Maybe the whole driver board could be replaced but would have to fit in the same restricted space.

enter image description here

Driver lives under the upper right white housing:

enter image description here

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    \$\begingroup\$ Most likely the electrolytic capacitors are loosing capacitance and increasing ESR. Try replacing them with same rated capacitance and same or higher voltage rating from some reputable manufacturer and report back. It’s the blue-green cylindrical thingamajingy at the left side in the top picture. Pay attention to the polarity when replacing it. \$\endgroup\$
    – winny
    Nov 30, 2019 at 13:34
  • \$\begingroup\$ @winny so if I test one of the caps I should its actual capacitance is far too low, is that right? \$\endgroup\$
    – StayOnTarget
    Nov 30, 2019 at 13:36
  • \$\begingroup\$ Most likely yes. Could theoretically be too high ESR with capacitance still within rating, but it’s unlikely. \$\endgroup\$
    – winny
    Nov 30, 2019 at 13:53
  • \$\begingroup\$ Have a look for an EZM328 meter on eBay. They're very cheap $10/$10 and very useful for occasional jobs such as this. \$\endgroup\$
    – Transistor
    Nov 30, 2019 at 18:45
  • \$\begingroup\$ It's probably not economical to attempt major repairs. If you've got time and resources, capacitor swaps might be acceptable. I wouldn't think it's worth replacing the driver with a custom design. \$\endgroup\$
    – user2943160
    Dec 1, 2019 at 0:01

2 Answers 2

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It could be a capacitor or other component in the driver, but it could be also a bad LED or a bad solder joint on the LED PCB.

You can try looking at the LED PCB:

  1. If all the LEDs are in series, then one dead LED will open the whole circuit and all LEDs will turn off. You can't know whether the fault is in the driver or in the PCB. Thermal expansion and cooling can make a bad contact intermittent and it can cause blinking.

  2. If they are wired in several series/parallel strings, then one dead LED will only open one series string, and that wouldn't make the whole lamp blink, only part of it. In this case, the fault is most likely in the driver.

In case 1, you need to find out if the fault is in the driver or in the LEDs. Since you already opened the light, simply power it up and probe the wires going to the LEDs with a multimeter. If you got a stable voltage but no light, blame the LEDs. If you got no voltage or unstable voltage, blame the driver, unless the LED board is shorted, but that would be unlikely.

You can estimate voltage by counting LEDs in series. Each white LED is about 3-3.5V.

You can also replace the driver with one from a working lamp to narrow it down.

If the driver is gone, most likely cause is the big capacitor, but it only takes a few minutes to perform these checks.

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When experiencing this slow 'death' of the LED driver it would very likely be the electrolytic capacitor slowly getting bad (it's electrolyte drying out). I don't see any damage to the driver IC or other components.

You could desolder it and measure it's capacitance if your multimeter allows you to do so. An ESR meter would also reveal how the capacitor is doing, but it is not a tool everybody has access to.

Alternatively simply replace it with a matching capacitor with the same capacity and >= voltage rating.

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