Power Supply Repair (EAY64509202, LGP27-16PIT) - Page 1
Forum section: electronics / repair

author: KejuBartin
author_rank: Newbie
timestamp: May 14, 2023, 03:02:10 pm
content: Hello everyone,I was sitting in front of my computer when suddenly my monitor (LG 49WL95C-W) turned off. I opened it and started troubleshooting. It looks like the power supply is the problem because if you connect it to power, the fuse blows immediately.I live in Germany and therefore the power supply receives 230V AC RMS. It outputs 20V DC. I started doing some measurements and analyzing the circuit and the power supply has a short circuit after the capacitor on the DC side.Two names to find the Power supply in the internet: EAY64509202, LGP27-16PITNow I don't know how to continue finding the problem. Does anyone have any ideas what the problem could be? Or any help/advise in general? Feel free to ask any questions.(I am a beginner in electronics and have tools like a digital multimeter, lab bench power supply and an oscilloscope.)Images of the PCB are provided below. I took two pictures of one side of the board to be able to read text better.Many thanks in advance,KejuEdit: better text formatting, added part numbers.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 14, 2023, 03:13:23 pm
content: By "after the capacitor on the DC side" do you mean:1. C611?2. Does it read short at C611, or only somewhat after C611 and any circuits between that and the DC side?It could be C611 or some switching transistor on that rail. Remove and check C611, and measure the resistance of the circuit with C611 removed.

author: KejuBartin
author_rank: Newbie
timestamp: May 14, 2023, 03:33:51 pm
content: As you can see by the arrow in the picture below, its this capacitor (C611). It's positive terminal is connected to "CAP +" that I wrote onto the PCB through the fuse that always blows immediately on power up. From that point after the fuse it's shorted to the negative terminal of the capacitor.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 14, 2023, 05:44:32 pm
content: I posted a replay and them removed it because I didn't realize there were two fusesTomorokoshi is problably right, check the switching transistors or the bulk cap.

author: lutprodic
author_rank: Newbie
timestamp: September 23, 2025, 03:59:10 pm
content: Hey, did you ever find out what was wrong with the power supply? I'm trying to fix the same one

author: MathWizard
author_rank: Super Contributor
timestamp: September 23, 2025, 06:51:12 pm
content: I highly recommend you make yourself a current limiter, with a +100W incandescent light bulb in series with the DUT. You also can get a fuse, household wall switch, plug (maybe they have a fuse in them in Deutschland), and light bulb socket. I put all those on a 2x4 piece of wood, and with a nice heavy cord. Then I can also use it with my isolation transformer and/or auto-transformer.But just with the bulb, any time your DUT is low resistance or a short, all that happens is the light bulb starts to glow or light up. It's great for all kinds of testing.And in instead of the light bulb, you can also put a wire break-out in the socket, and either put a wire nut on it, and have a nice wall socket and fused wall switch on or by the bench. And sometimes I've just use those leads to hook up to for some reason.Oh this is an old thread, I hope the OP made it safely to the present.If you know the safety basics, you could just start probing for voltages, like on all the power rails, and to the Vcc pins. Or first you can check a lot of stuff un-powered.Whats the problem with the monitor ? I'd recommend soldering on some GND wires, on the hot mains powered side, and on the GND of the output side. There may be more than 1 output common node tho, for the various output rails.I'd also solder wires onto some key places, rather than going free-probing on mains powered high-voltage stuff. There might be pretty high voltages on the output side too, IDK these monitors, but I've seen LED TV's with 300V output w/ no load anyways. If you don't know much about these circuits, and whats what, I'd avoid a lot of places, or attach wire probes 1st, then hands-free, stand back and power it up with a switch.Look at the voltage rating on the various output caps, to get an idea of the voltages, and look up IC's and regulator part #'s to get there likely voltages and pinouts.

author: Li Yang
author_rank: Newbie
timestamp: September 25, 2025, 04:02:25 am
content: if Q101 and Q102 have already broken down...

author: asis
author_rank: Frequent Contributor
timestamp: September 25, 2025, 07:56:39 am
content: Hi,&SSC3S921 Sankenhttps://datasheet4u.com/share_search.php?sWord=SSC3S921