Cheap CFL teardown after failure

[mariushm]

Nice... reminded me of the two cfl lightbulbs I posted a while ago here.

Now that I have an ESR meter I decided to have a second look at one of them - on the other the glass broke.

So removed the main capacitors from the pcb and the one by the lamp wires - i forget how it's called.

The main ones are 3.3uF 250v, one is open and the other has 15 ohm esr and 2.6uF capacity. The green one is toast, open. Brand is some no-name with letters c and y inside a diamond shape.

Too much to bother fixing, esp. as I don't have the replacements around. And... the other green cap on the board is probably also toast.

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[ben7]

Originally Posted by mariushm

Nice... reminded me of the two cfl lightbulbs I posted a while ago here.

Now that I have an ESR meter I decided to have a second look at one of them - on the other the glass broke.

So removed the main capacitors from the pcb and the one by the lamp wires - i forget how it's called.

The main ones are 3.3uF 250v, one is open and the other has 15 ohm esr and 2.6uF capacity. The green one is toast, open. Brand is some no-name with letters c and y inside a diamond shape.

Too much to bother fixing, esp. as I don't have the replacements around. And... the other green cap on the board is probably also toast.

Attachment 41768

Attachment 41769

Looks like there is no fuse either!
BTW, what about that smaller black cap?

[budm]

20Watts lamp driven by small high voltage TO-18 Plastic MOSFET's and no fuse, enclosed in a seal case while using the lamp with base up? No wonder they failed.
And it has CE?

[mariushm]

I didn't bother to check, after finding those two flaws already.

But yeah, just for you i pulled that capacitor out... 4.7uF 50v ... came out as 4.89uF 11.7 ohm esr

No name cap, what would you expect?

[Behemot]

We got one CCFL at home which managed to last something arround 10 years. No kidding…but it cost something back in the 90s

Anyway, CCFLs I have seen got usually failing caps, one even failed Rubycon with some 4000/5000 hours rating. Polyswitch poped in half there. Tried to repair but screwed somehow Will ask here when theres thread

[ben7]

Originally Posted by Behemot

We got one CCFL at home which managed to last something arround 10 years. No kidding…but it cost something back in the 90s

Anyway, CCFLs I have seen got usually failing caps, one even failed Rubycon with some 4000/5000 hours rating. Polyswitch poped in half there. Tried to repair but screwed somehow Will ask here when theres thread

I dont think they usually have polyswitches, I have seen some capacitors which do look like polyswitches though. If one of the diodes or transistors are open/shorted the rest are guaranteed to go pop xD

[Behemot]

Yes, it was polyswitch, I think I even asked here what it is and eventually found it in local shop. But as I said, screwed somehow…

[Th3_uN1Qu3]

"Moon" brand CFL, 18W. Failed about a month ago, finally bothered to see what's wrong with it. Tube didn't go dark at the ends so this was definitely an electronic failure. 1N4007 bridge, 4.7uF 400v "Hlicon" primary cap. No fuse, but there is a necking of the trace leading from one of the AC wires to the diode bridge, which in the event of a short downstream should act like a fuse and blow out. Hopefully.

I first thought that 1nF film cap in pic 4 looked a bit suspicious (browned), but pulled and tested good, so i put it back. Tried it again, still no go. There was voltage on the main cap, so obviously for a reason the circuit wasn't oscillating. I pulled the switching transistors (13002s made by "Success Technology" in Shenzen ), and they tested good. One interesting thing that happened was that while desoldering the first transistor, i accidentally shorted it C-E with my iron, and the lamp struck briefly from the energy left in the primary cap. Hmm.

The reason for failure was the 680kOhm resistor behind that transistor (pic 3), which tested open. It was wired guess where? Between C-E. It obviously was responsible with the startup of the oscillator. I didn't have a 680k so i used 2x 360k in series. Lamp is now working fine. Due to the slightly higher startup resistor it does take a little longer to strike compared to the other one in the same fixture, but that's fine with me, i can't be bothered to take it apart again.