FAQ
TL;DR: Most 220–240 V LED bulb failures trace to LEDs themselves (99%); “In 99% of cases, one (or several) of the LEDs fails.” Use a meter to check LEDs, bridge, SMD fuse, and electrolytic. [Elektroda, 398216 Usunięty, post #16745046]
Why it matters:** This FAQ helps DIYers diagnose and repair mains LED bulbs safely with a basic multimeter and soldering tools.
Quick Facts
- Failure breakdown: 99% LEDs, 1% electrolytic/rectifier bridge. [Elektroda, 398216 Usunięty, post #16745046]
- Driver type: simple capacitive dropper at 50 Hz; check the SMD fuse first. [Elektroda, Krzysztof Kamienski, post #16746278]
- Bridge rectifier check: use ohmmeter/diode mode “as with LEDs.” [Elektroda, 398216 Usunięty, post #16745288]
- Visual cue caveat: a tilted electrolytic can look bulged—verify before condemning. [Elektroda, marian1981.02, post #16746319]
- Field fix example: shorted one of 48 series LEDs restored operation for a month. [Elektroda, cirrostrato, post #16746407]
What usually burns in a 220–240 V LED bulb?
LED chips are the dominant failure point. One expert notes, “In 99% of cases, one (or several) of the LEDs fails,” with the remaining 1% split between the electrolytic capacitor and the rectifier bridge. [Elektroda, 398216 Usunięty, post #16745046]
How do I test the rectifier bridge with a universal meter?
Use diode-test or ohmmeter mode. Check each junction like testing diodes: forward conduction one way, block the other. Confirm no shorts between AC and DC pins. If any leg reads both ways or always zero, replace the bridge. 3-step: 1. Isolate board power. 2. Probe all four legs in pairs. 3. Compare readings symmetrically. [Elektroda, 398216 Usunięty, post #16745288]
What is a capacitive dropper LED driver?
It limits LED current using the reactance of a film capacitor (e.g., CBB22) at 50 Hz instead of a switching converter. These bulbs often include an SMD fuse and an electrolytic smoother after rectification. Start checks at the SMD fuse. [Elektroda, Krzysztof Kamienski, post #16746278]
How likely is the electrolytic capacitor to be the culprit?
It is an uncommon cause compared with LED failure. The reported split is 99% LEDs versus 1% for the electrolytic and rectifier bridge combined, so prioritize LED testing first. [Elektroda, 398216 Usunięty, post #16745046]
My electrolytic looks bulged—should I replace it?
Not always. A crookedly soldered capacitor can mimic bulging. Inspect from multiple angles, then measure or swap only if you confirm a fault, rather than judging by tilt alone. [Elektroda, marian1981.02, post #16746319]
Which protective part should I check first on a dead bulb?
Check the SMD fuse before deeper troubleshooting. In capacitive-dropper designs, a blown SMD fuse is a straightforward open-circuit failure that stops everything. [Elektroda, Krzysztof Kamienski, post #16746278]
The LEDs test fine—what should I probe next?
Move upstream. Verify the SMD fuse continuity, then test the rectifier bridge, and finally the electrolytic smoother. This sequence matches typical failures in capacitive-dropper bulbs. [Elektroda, Krzysztof Kamienski, post #16746278]
Can I bypass a single dead LED to bring the bulb back?
Yes, in series strings a single short can restore operation. One user shorted one failed LED in a 48-LED chain and it worked for a month. Use this as a diagnostic or low-stakes fix. [Elektroda, cirrostrato, post #16746407]
An SMD resistor near the capacitor reads open—what does that indicate?
It suggests a failed current-limiter or sense resistor. This open prevents current flow even when LEDs look fine. Replace the open SMD resistor after confirming identification and value. [Elektroda, mitlex, post #16746321]
How do I measure parts if I’m new to multimeters?
Start with your meter’s manual and basic guides for measuring resistors and capacitors. Knowing the correct ranges and modes prevents misreads and damage during diagnosis. [Elektroda, tomek5333, post #16744950]
How should I verify a film capacitor CBB22 400 V with basic tools?
With only a simple meter, in-circuit capacitance checks are unreliable in dropper designs. Focus on upstream checks: SMD fuse continuity, then bridge and electrolytic evaluation, before suspecting the film capacitor. [Elektroda, Krzysztof Kamienski, post #16746278]
If LEDs and bridge test okay, what else can fail?
Look for an open SMD fuse or resistors in the dropper network. These parts can silently open and mimic LED failure while all diodes test fine. [Elektroda, Krzysztof Kamienski, post #16746278]
Is there a quick way to confirm LED string health?
Inspect for visibly burnt LED chips and test continuity across each LED. A single open device in a series chain breaks the whole lamp. Replace or temporarily short the bad LED to confirm. [Elektroda, 398216 Usunięty, post #16745046]
Does a bridge rectifier ever fail partially?
Yes. A single shorted or leaky diode leg inside the bridge can cause flicker or no light. Your diode-test should show asymmetric readings; identical both-way readings indicate failure. [Elektroda, 398216 Usunięty, post #16745288]
Why does shorting one LED work in some repairs?
Series strings stop on a single open. Bridging the failed LED restores continuity, proving the rest of the circuit. “Shorted the defective and have been illuminating… for a month.” [Elektroda, cirrostrato, post #16746407]
Are skewed components a manufacturing defect or damage?
Often it’s just assembly misalignment. A skewed electrolytic can look swollen, but function fine. Confirm with electrical tests, not appearance alone. [Elektroda, marian1981.02, post #16746319]
