LG 65" OLED No Power - Page 1
Forum section: electronics / repair

author: epsoft
author_rank: Newbie
timestamp: June 27, 2025, 04:41:00 am
content: Hi all, newbie here asking for some assistance. Please be gentle!Got a 4 year old LG 65" OLED TV that has died. No standby LED and not detecting any standby voltage out of the PSU. Prior to going completely dead, it worked for a couple of months if turned off at the wall for a few seconds. Read elsewhere that it could be the two 800nf caps next to the bridge rectifer. Pulled them and tested, sure enough one was approx 500nf, the other 50nf. Figured I had this cracked, replaced both, no change. Getting what looks like all the right readings on the hot side, but nothing on the cold side. Reaching the limit of my abilities to diagnose further, what else can I check?

author: FIXITNOW2003
author_rank: Regular Contributor
timestamp: June 27, 2025, 06:43:50 am
content: repair kits on line maybe easiest option ..https://www.ebay.co.uk/itm/256870435833?var=557405361125&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5339055791&toolid=20006&_ul=gb&customid=CjwKCAjw3_PCBhA2EiwAkH_j4tcW1lz-OTKSX5FnJlcSj1KpcsA9UntvImHw0a7qfpLSmNDu-ksf5BoC40gQAvD_BwE|0AAAAAC5ena3q1wOde07n27mSU4jdG1CSd|Cj8KCQjw3_PCBhCSARIuAPkxe-BLUWm155PbCTeNdgQJuLS9tOPMAwnSLxMXK-cbKTZnc9HFxi8cggnRQBoCNRE|v1&gclid=CjwKCAjw3_PCBhA2EiwAkH_j4tcW1lz-OTKSX5FnJlcSj1KpcsA9UntvImHw0a7qfpLSmNDu-ksf5BoC40gQAvD_BwE&gbraid=0AAAAAC5ena3q1wOde07n27mSU4jdG1CSd&wbraid=Cj8KCQjw3_PCBhCSARIuAPkxe-BLUWm155PbCTeNdgQJuLS9tOPMAwnSLxMXK-cbKTZnc9HFxi8cggnRQBoCNRE&gad_source=1&gad_campaignid=21642694552

author: epsoft
author_rank: Newbie
timestamp: June 27, 2025, 07:21:29 am
content: Thanks for the tip, if nothing else it gives me some ideas of what to check.

author: coromonadalix
author_rank: Super Contributor
timestamp: June 27, 2025, 11:18:50 am
content: normally try to find chassis or model related Service manuals if any, check for the standby voltages / constant voltages, and check if you can trigger on the psusome models have a pin you pull up or down to power up all the sections ?could be the psu or the backlight section ....dont change parts for nothing hoping it may resolve the issue, it's a 50/50 guess

author: epsoft
author_rank: Newbie
timestamp: June 27, 2025, 11:49:15 am
content: Thanks coromonadalix, I'm not getting any voltages on the cold side of the power supply, no standby, nothing. I replaced the two 800nf caps as they tested way out of spec. If I could find a standby voltage I would try triggering it on but can't even try that at the moment. The kit suggested above by FIXITNOW2003 has given me some clues to other components to test but I won't replace them unless they actually test bad. I could just get a whole new power supply for about $300 AUD but where's the fun in that? lol

author: Psi
author_rank: Super Contributor
timestamp: June 27, 2025, 12:38:40 pm
content: From a general switchmode perspective two things i would check are1) The boot strap resistor if it has one, they are usually like 100k to 470k. and you may see some discoloration around them due to repeatedly getting hot.2) The opto isolator. I've seen them fail a few times.

author: epsoft
author_rank: Newbie
timestamp: June 27, 2025, 12:56:50 pm
content: Thanks Psi, I'll check those too

author: MathWizard
author_rank: Super Contributor
timestamp: June 27, 2025, 05:02:25 pm
content: For sure there will be a bunch of SMD stuff on the bottom of the PCB, with the controller IC's, I don't see any on the topside. I'd check as much unplugged as I could, then if when powered up, if most of the hot-side voltages seem good, I'd look up the controller IC's, find their pinout, and see what they are doing. Really you would want an oscilloscope.Somewhere there should be some Standby voltage on the cold side, if that's missing too, I'd focus in on those circuits. It often has a separate little switching transformer and controller IC just for the STBY power. And on a lot of devices, those circuits will also make the low voltage supply, like 10-15V, for the IC's on the hot side.It could be a cracked solder joint, or something else that temperature might effect. Did tapping or smacking the TV/PCB ever get it to work again ? (I would not want to smack a big TV, but I would the PCB)Safety-wise, if you find these controller IC's, and have a soldering iron, you may want to solder on some wires, like a GND on the hot, and cold side, so you don't have to go poking at live circuits, especially on some fine pitch IC, it's too easy to short pins (I've hardly ever done it, but it's a wonder).

author: coromonadalix
author_rank: Super Contributor
timestamp: June 27, 2025, 06:28:11 pm
content: service manualhttps://research.encompass.com/ZEN/sm/OLED65C1PUB.pdfcheck page 57If there is no vaild communication between CPU and MICOM for more than 5seconds, the MICOM switch off PSUPower Check Sequence1. AC input Check : 100~240Vac2. PWR-ON Check : P201- SET On : above 3V- SET St-by : 0V3. 12V Level Check : P201- SET On : 12V- SET St-by : 7.8V (swing between 7V to 10V)4. DRV_ON Check : P201- SET On : above 2.5V- SET St-by : 0V5. T-CON 22V Check : P251- SET On : above 22V- SET St-by : 0V6. T-CON 12V Check : P252- SET On : above 12V- SET St-by : 0VAll condition meets, Power Board OKwhen you search the psu pcb model you find many answers like : where the power supplies do not run properly. The C601 and C602 with the yellow capacitors 820nF 500V are largely culprits...https://www.iwenzo.de/threads/lg-oled65xxx-oled77xxx-keine-funktion.75351/

author: epsoft
author_rank: Newbie
timestamp: June 28, 2025, 12:21:19 am
content: Thanks coromonadalix, I had read about C601 & C602, pulled those out and they tested bad, replaced them but didn't fix the issue.Will try the trouble shooting steps you suggested, could be I'm just a bit slow and it's shutting down before I get to the right pins to test

author: epsoft
author_rank: Newbie
timestamp: June 28, 2025, 12:45:39 am
content: Thanks mathwizard,The story is the TV was working fine up until a few months ago, then it stopped turning on via the remote and the only way to get it to turn on was to unplug it from the wall and plug it back in. This worked for a few months before it died completely. After some Googling I came across the C601/C602 issue which seemed to fit my symptoms, pulled them out and they tested bad so I figured I had found the culprit. Replaced them but no difference, hence I'm here looking for advice and next steps.I don't have an oscilloscope unfortunately, although this might give me a good excuse to purchase one!I should mention, I could just replace the whole board for about $300 and may end up doing that anyway. I just thought this should be a fixable problem, and secondly, I want to be sure it's actually the power supply and not the main board as that's another $300 to replace.I'm just one of those people that doesn't like throwing things away when they can be fixed. We have a spare, smaller TV to use in the meantime so it's not urgent. I'm mostly doing this for the experience rather than trying to save a few $$.

author: MarkusAJ
author_rank: Contributor
timestamp: June 28, 2025, 03:03:19 am
content: Quote from: epsoft on June 28, 2025, 12:21:19 amI would check all electrolytic capacitors and diodes in low voltage section. The diodes are probably schottky.In many cases failing short capacitor will damaged the rectifier.When you replace electrolytic capacitor in this power supply, make sure it's low ESR capacitor for switching power supply.

author: epsoft
author_rank: Newbie
timestamp: July 01, 2025, 12:53:50 am
content: I pulled the other yellow CARLI capacitors to test. Here are the results:Note: Tested with LCR-TC2 component tester and MESR-100 capacitor meter (LCR-TC2 ESR was way off)CARLI MPC 824J 500V - 820nf (tested 60.51nf with ESR 30) - Replaced as mentioned in original postCARLI MPC 824J 500V - 820nf (tested 588.0nf with ESR 2.9) - Replaced as mentioned in original postCARLI MPC 824J 500V - 820nf (tested 899.0nf with ESR 1.6) - New cap for referenceCARLI DMB 333J 800V - 33nf (tested 36.88nf with ESR 52)CARLI DMB 223J 1000V - 22nf (tested 24.26nf with ESR 82)CARLI DMB 223J 1000V - 22nf (tested 23.83nf with ESR 83)My observations:The first 824J was toast, very low capacitance and high ESRThe second 824J was on it's way out, low capacitance and rising ESRThe 333J and 223J's, ok capacitance but high ESRThe LCR-TC2 is useless for testing ESR, at least with these MPC capsI'm thinking I should I replace the 333J & 223J's, is that likely to fix my issue?