Flyback transformer identify? - Page 1
Forum section: electronics / repair

author: ne1hobby
author_rank: Newbie
timestamp: August 19, 2024, 07:25:44 pm
content: Requesting help to identify this part which I believe to be a flyback transformer. It powers a G4T5 florescent UV bulb via 4 AA batteries. The device also has a "turbo" button to momentarily increase the power when held down to brighten the bulb. The only identification on this 6 pin component is the core description "A100" and "3C81", nothing under the yellow tape. Any ideas on how I can spec a new one?

author: squadchannel
author_rank: Frequent Contributor
timestamp: August 20, 2024, 12:28:51 am
content: most transformers are custommade, it is unlikely that the same transformer will be sold individually.You can use an LCR meter to measure inductance, etc., and obtain a transformer with similar specifications, or you can disassemble the transformer, unwind the windings, and duplicate the same one.3C81 is the core material.

author: TimNJ
author_rank: Super Contributor
timestamp: August 20, 2024, 02:19:13 am
content: It is unlikely the transformer has failed unless it is poorly designed and runs extremely hot. Or if it was subject to mechanical stress/shock. Semiconductors are much more suspect. Check MOSFETs, diodes, and ICs for shorts.It looks like an ‘EP’ type core, but again, probably not your issue.

author: ne1hobby
author_rank: Newbie
timestamp: August 20, 2024, 12:02:40 pm
content: Thanks for the insights. The reason I think it needs to be replaced is that on 3 of these 10yr old UV lights, if I give this part a whack it will start working again short term. Solder joints appear fine and no other component on the board looks suspect.

author: TimNJ
author_rank: Super Contributor
timestamp: August 20, 2024, 03:25:04 pm
content: Quote from: ne1hobby on August 20, 2024, 12:02:40 pmI see! You might want to give it a squeeze in the axis in the attached photo, but only with proper insulating linesman leather/rubber gloves! The two core halves could be loose. Or there could be a micro-fracture in the core somewhere, which will not be visible. Giving the core a squeeze may prove that it's a core related issues.It would be safer to simply remove the transformer and try the same squeezing, but with an LCR meter attached across the primary winding. If you see inductance changing all over the place, then there's some damage to the core. If you don't see much change, I guess some wire could be broken, although that seems unlikely.If it's a core issue, you could get a new core and grind a new air gap. Check the inductance of the primary winding of a good unit, and/or measure the air-gap length directly (with a caliper) to see exactly how much material you need to remove. You'd need a diamond file or a diamond wheel for a Dremel. You may wind up spending more money than the unit is worth to get the grinding supplies. But, if you love the light, you could do it. (EP core type below.)

author: ne1hobby
author_rank: Newbie
timestamp: August 23, 2024, 01:32:34 pm
content: No luck with the squeeze, I'm going to assume its intermittent issues with the transistor next to it or a wire I can't see under the transformer. $200 UV lights so I'm going to start replacing components until they work! Thanks again all!