LG Monitor Power Supply Design - Page 1
Forum section: electronics / general

author: andresj551
author_rank: Newbie
timestamp: June 23, 2019, 03:15:43 am
content: Hello!I have bought an used monitor, it worked ok until it started to "blink" before showing anything on the display. I first thought it was a capacitor on the display itself, so I open it and couldn't see anything wrong.After a while it got worst and took several minutes to "start up" with a noticeable high pitch noice. Then I decided to check again, this time looking to the voltage of the power supply (an external brick) and as you can expect it was dropping the voltage at the minimum sight of load.I had to open the sealed power brick and noticed a bad capacitor. At this point I didn't want to fix the power supply, because the seal is broken and already have another 19V brick.I attached the image of the LG power supply for the monitor Flatron E2342. Let me know what you think about the main capacitor been so close to that heatsink...(The almost exploded capacitor has been removed and disposed, it was the same brand as the 450V one)

author: MrMobodies
author_rank: Super Contributor
timestamp: June 23, 2019, 05:56:27 pm
content: The left leg already looks like it is touching.When you took it apart did it have no shielding on it?Well I was thinking:Is that heatsink earthed or not?If you were to put some pressure or squeeze both sides of the plastic will it the make heatsink push forward and touch the other leg.

author: andresj551
author_rank: Newbie
timestamp: June 23, 2019, 08:41:09 pm
content: If it drops or gets squeezed (by stamping on it) it could be posible to short circuit that capacitor.I have mesured the heatsink for continuity (no shield at all from factory) and it'snt earthed but connected to the negative leg of the capacitor.

author: MyHeadHz
author_rank: Regular Contributor
timestamp: June 25, 2019, 01:50:56 pm
content: I don't know about the technical details of the spacing, but I do have a different revision of that power supply. In mine, there was very little heat sink thermal capacity, but it was otherwise similar. I wondered to myself why that was because it got quite hot and would obviously decrease the lifespan of the device.Your pictures actually seem to answer those questions. They added the thermal capacity in aluminum heat sinks, then crammed everything else together more tightly to make room. Since yours eventually failed in the same way, it seems like a failed attempt. They added thermal capacity without adding a way to get that heat out of the device, so yours ultimately failed in the same way mine did.I replaced the capacitor in mine and sealed it back up. It hasn't had any problems since, but I know it is only a matter of time with this thermal design.FWIW this monitor was the first, and will be the last, monitor I buy with an external power supply. They are cheaper to buy, but not worth it. They are less reliable and they are more difficult/annoying to fix when they fail. It is also annoying because so few monitors use an adapter, and there are many standards for such adapters. With standard monitors, there is just one standardized cord so it's super easy. Lesson learned...

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 25, 2019, 04:02:26 pm
content: Quote from: MyHeadHz on June 25, 2019, 01:50:56 pmThe smaller ones that use external power supplies are great for converting to run on battery power. Combine that with a wireless HDMI kit or small computer and you end up with a rather handy gadget.

author: andresj551
author_rank: Newbie
timestamp: June 25, 2019, 04:09:16 pm
content: QuoteI replaced the capacitor as well, but it makes a horrible noice (high pitch sound) so I took all parts from it.QuoteI will make mine run from solar somehow. For now I don't even have a solar pannel or place to put it.

author: SteveyG
author_rank: Unknown
timestamp: June 27, 2019, 06:33:09 am
content: Unfortunately PSU design has many compromises - people want small form factor, but the only way to achieve that is by cramming everything in. That said, unless that capacitor is seeing a very high ripple current, it should still last several thousand hours under load which is enough these days for most consumer equipment. The high efficiency converters help with reducing the overall heat and it's unlikely the capacitor is seeing hugely excessive temperatures.Not a lot you can do...