What inductor to replace LCL filter in power supply? - Page 1
Forum section: electronics / repair

author: wardrop
author_rank: Newbie
timestamp: July 22, 2020, 02:19:08 am
content: Hi all,I'm just repairing a power supply in my Hisense TV. It seems the very first inductor (an LCL filter) has shorted. I'm just struggling to know what kind of inductor/choke/filter I need to replace it with. I've even considered just bypassing it altogether. See the attached pictures.The pins are 7mm apart on each side, with 9mm between the input side and output side.Any help is much appreciated.Cheers,Tom

author: wardrop
author_rank: Newbie
timestamp: July 23, 2020, 01:10:32 am
content: No one knows? Is it safe to bypass this inductor? My other option is to just buy a whole new power supply for ~$80.

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: July 23, 2020, 01:32:01 am
content: That looks like a common mode choke. If the core is ok I’d consider rewinding it. There doesn’t appear to be many windings.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 23, 2020, 01:32:46 am
content: Hi,You can remove the common mode choke and replace it with wire links for a test. This will tell you if the rest of the power supply is good.The choke you have is bifilar wound. One of the wires is normal magnet wire, the other wire is triple or quad insulated wire.If you have some suitable wire you might be able to rewind the broken one.If you run the TV with the choke shorted it may cause interference to other equipment. It looks kike there is a multistage filter so the interference may not be too bad. See if you hear interference with an AM radio.Regards,Jay_Diddy_B

author: wardrop
author_rank: Newbie
timestamp: July 23, 2020, 01:39:59 am
content: Thanks for the advice guys. Didn't even consider rewinding as an option. That might be the way to go.As for wiring over the choke to test the rest of the power supply, that also crossed my mind laying in bed last night. No point fixing or replacing this choke if there's more problems upstream. I just wanted to make sure doing so wouldn't damage any other componants.

author: aqibi2000
author_rank: Regular Contributor
timestamp: July 24, 2020, 09:31:12 pm
content: Please can you confirm what it have used to verify the Inductor is shorted or is it physically burntLCR Meter, ring tester, curve tracer?

author: wardrop
author_rank: Newbie
timestamp: July 24, 2020, 10:43:01 pm
content: I've checked the resistance with a multimeter and it's super low (0.002 ohms) between 3 of the pins and there's no continuity with the last pin, which coincidentally corresponds to the burn marks on the PCB. I bridged over where the inductor was and the TV and everything turned on, which further confirmed the diagnosis.I started to unwind the inductor and noticed on that "bad" pin it was completely cut/broken right at that one end, and the surrounding winding are also damaged.Now I need to find some double/triple/quad insulated wire to use as the secondary winding. Any ideas where I can get that from? The conductor is 0.5mm in diameter.

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: July 25, 2020, 03:10:25 am
content: As you have discovered, the choke is not required for the television to operate. If you do pursue rewinding and replacing the choke be very careful how the windings line up to the board pins. A mistake can short the mains power. FWIW, I'd just leave it out.

author: wardrop
author_rank: Newbie
timestamp: July 26, 2020, 02:34:10 am
content: Thanks @Groung_Loop, that's what I've done for the mean time anyway; have left it out. Got bigger fish to fry at the moment, and so far the TV's been fine without it, as has everything else around it and plugged into the same powerboard.