LG 37LE5900 TV - Random on/off cycles before powering on - Page 1
Forum section: electronics / repair

author: malc-c
author_rank: Newbie
timestamp: August 04, 2020, 11:15:24 am
content: Hi guys, hope you can provide me with some assistanceOur LG LED tv (37LE5900) is around 10 years old, and has been very reliable considering it's probably on for a good 18 hours a day every day in that period. However recently it's developed a fault where it won't turn on first time, either from the remote or from the touch sensor on the front. If you press the power button on the remote, you hear a tick like a relay close as normal, then the adjustment button illuminations sequentially light up, finishing with the LG logo. But no picture or sound. Press the power button again, and the reverse happens. You can continue to do this and eventually the set will turn on and work fine, but it can be between 2 and 12 cycles.I removed the back panel and looked at all the capacitors on the power supply, as most of my googling the issue suggested it was the PSU that is the issue. None of the electrolytics are bulging or show any signs of leakage. Anyway, I noted down their values and can sizes so I can see about sourcing replacements if required. There were two large caps that were not electrolytics, M105J 500v and M183J 800v, would these be metalzed film capacitors ? and would they be the ones that are more likely to fail ?Anyway, I dusted off the board, made sure the connectors were all in correctly and were not loose, and then put the back on and powered up the TV - To my surprise it came on 1st time. I turned it off and back on and again no issue - Yeah, I fixed it I thought... well three days later its doing the same issue again. I did notice though that after my clean and inspection, there was a delay between pressing the power button on the remote and the illumination sequence to power off then when the issue occurs, by that I mean the power on and off sequence of illumination of the control touch pads happens straight away when the set fails, but if it takes a while to power down (as if saving settings) it tends to turn on without an issue if the power button on the remote is pressed again straight after.With regards to the capacitors, two of them are 68uf 450v and are around 50mm long and 12mm diameter. Is there any reason for this long can? Could I replace them with capacitors of the same value, but in shorter cans, like the more common 20mm tall ones, or is there a reason why these caps are 50mm tall? Also, given the issue described, is it worth replacing all the capacitors, or is the issue likely to be just the two metal film capacitors?Cheers, and please be nice. I'm no expert, but I'm quite capable of desoldering and replacing a bunch of caps

author: goaty
author_rank: Regular Contributor
timestamp: August 04, 2020, 11:50:57 am
content: From what I´ve seen, the form of the caps is because they need to be very low profile inside the housing of the TV.I guess replacing Caps could help, but it´s not always the case. I recently repaired a device where a diode had developed reverse leakage which was hard to troubleshoot.

author: tunk
author_rank: Super Contributor
timestamp: August 04, 2020, 12:17:07 pm
content: Bad solder joint or contact somewhere?