Fluorescent Lamp Inverter - Page 1
Forum section: electronics / repair

author: JDW
author_rank: Frequent Contributor
timestamp: August 21, 2019, 09:43:41 am
content: The following URL hosts some photos of a Fluorescent lamp I've been using for about 13 years. It's been working fine until recently. It now won't power on. I recently changed the tube so I know that is good. I confirmed the push switch is good. The fuse on the inverter circuit board checked out good. Yet it won't power on. I know nothing about how these inverters work, so I'm not sure how best to test it further, hence my post here.https://www.icloud.com/sharedalbum/#B0w52plgjNZIflI thought the small electrolytic capacitors (C5 & C16) might be leaking, so I replaced them but the lamp still won't power on. And I know the power cord is good because I can measure the correct wall voltage coming through it to the circuit board.Any testing tips or suggestions you could give me would be appreciated.Thank you.

author: goaty
author_rank: Regular Contributor
timestamp: August 21, 2019, 09:48:24 am
content: If you have a multimeter you could check the diodes and transistor for shorts and alike. I had one repaired where the power transistor (like your 2SC4546 NPN) was shorted.

author: JDW
author_rank: Frequent Contributor
timestamp: August 22, 2019, 09:55:41 am
content: Quote from: goaty on August 21, 2019, 09:48:24 amThanks.Diodes D1, D2, D3, D4 and D5 all show their forward voltage just fine with my diode checker, tested in-circuit. I desoldered the 2SC4546 (NPN BJT) and put it on a breadboard and wired it up to switch GND to a test LED and it worked fine.Any further thoughts?

author: JDW
author_rank: Frequent Contributor
timestamp: August 28, 2019, 06:21:54 am
content: I guess I've stumped the experts here!Perhaps some electronics aren't meant to be fixed.Thanks.

author: fzabkar
author_rank: Super Contributor
timestamp: August 28, 2019, 06:41:02 am
content: I would check the capacitance of the film caps. I also make it a practice to reflow the solder joints at all coils and transformers.

author: JDW
author_rank: Frequent Contributor
timestamp: August 28, 2019, 09:20:17 am
content: Quote from: fzabkar on August 28, 2019, 06:41:02 amThank you for the advice.I removed all 6 film caps and measured the correct capacitance on all of them, as per their markings. Not sure what ESR should be, but measuring with my DE-5000 at 100kHz, ESR on most of them were under 1-ohm, although C15 was about 2.5-ohms at that frequency. Not sure if that is high or normal.I then reflowed the solder joints at all coils and transformers and then tested. Still a NO-GO. My lamp won't light.Any further ideas would be appreciated.

author: soldar
author_rank: Super Contributor
timestamp: August 28, 2019, 09:57:45 pm
content: Ifr you really want to spend time on this project I would start by reverse engineering the schematic.But IMHO, if you want to be practical, I would go for an LED replacement.

author: james_s
author_rank: Super Contributor
timestamp: August 28, 2019, 11:14:02 pm
content: Those are usually based on a Royer oscillator. Look for dipped film capacitors, especially if there is one across the fluorescent tube to allow current to flow to heat the cathodes before the tube strikes. I remember years ago I repaired quite a few of those curly CFL bulbs just because I could and often I'd find one of those film capacitors had shorted.

author: QQE06-40
author_rank: Newbie
timestamp: August 29, 2019, 08:45:52 am
content: Just a thought, because i had this happen several times before with SMPS's: check the higher ohmic resistores (>100k). They sometimes go o.c. with no obvious signs and for no obvious reasons. I see some of them on your pictures (R2/R22/R3/R4 e.g.). Have You checked R5? Seems to be a low ohmic fuse-resistor from the emitter of the switching transistor to ground.Greeting,Wolf

author: Kartman
author_rank: Contributor
timestamp: August 29, 2019, 09:38:11 am
content: I’d second checking the resistors. The smaller resistors suffer from electromigration at higher voltages and go open circuit. I spied a couple of 330k resistors near the transistor - i’d suspect them.

author: JDW
author_rank: Frequent Contributor
timestamp: September 02, 2019, 09:40:12 am
content: Gentlemen, thank you for your suggestions.R5is marked "1R0J 1W" and measures1.3ohmsin-circuit. It is light in color and easy to see there are no visible burn marks. So this part would appear fine.R24measures 98.3k in-circuit. Bands indicate it is a 100k. So this too is OK.R22measures 231k in-circuit. Bands indicate it is a 240k. OK.R2measures 332k in-circuit. Bands indicate it is a 330k. OK.R3measures 325k in-circuit. Bands indicate it is a 330k. OK.R4measures 322k in-circuit. Bands indicate it is a 330k. OK.R7measures 33.5 in-circuit. Bands indicate it is a 33ohms. OK.That seems to be all the resistors. No problem here.The 3 blue color caps are not "dipped film" that I can see insofar as they feel as hard as a rock and I must assume them to be ceramics. I didn't test these yet but there is not visible cracking on any of them.Hmmm...

author: james_s
author_rank: Super Contributor
timestamp: September 02, 2019, 03:48:00 pm
content: Film caps are hard as a rock too, and when any of these fail you can't tell just by looking at them.

author: JDW
author_rank: Frequent Contributor
timestamp: September 03, 2019, 09:23:59 am
content: Quote from: james_s on September 02, 2019, 03:48:00 pmI desoldered all the blue caps and tested outside the circuit:C8: Marked "104U" and measured 102nF, ESR=7.8-ohm @120HzC9: Marked "474" and measured 473nF, ESR=2.9-ohm @120HzC25: Marked "184" and measured 183nF, ESR=8-ohm @120HzNo problem here.

author: xmetal
author_rank: Contributor
timestamp: September 03, 2019, 10:15:21 am
content: I vaguely remember having a similar problem with a circuit like that some years ago. It turned out to be the input voltage to the device was too low.

author: JDW
author_rank: Frequent Contributor
timestamp: September 03, 2019, 10:22:17 am
content: Quote from: xmetal on September 03, 2019, 10:15:21 amIf by "device" you mean the entire PCB I've been talking about, let it be known that the voltage is a wall socket. It's designed for Japan to run on 100VAC at either 50Hz or 60Hz (since Japan uses both frequencies, depending on area).

author: xmetal
author_rank: Contributor
timestamp: September 03, 2019, 11:36:06 am
content: Quote from: JDW on September 03, 2019, 10:22:17 amI can't remember what the source voltage was on the device I was working on but it was lower than it should have been and was stopping the fluorescent from working. It created the same symptoms as yours so I thought it was worth pointing out.