Impressively bad TV PSU failure - Page 1
Forum section: electronics / general

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: December 22, 2017, 08:14:48 pm
content: I do TV repair at the age of 19, and someone brought this unit in today.Its a Seiki SE39Y04 4K TV and they said that flames shot at least 2 feet out of the TV, and of course I was intruiged.Here are a couple images of the aftermath:https://imgur.com/a/0GHBjThe fuse didn't blow either...Has anyone else had a power supply fail this badly without blowing the fuse?

author: German_EE
author_rank: Super Contributor
timestamp: December 22, 2017, 08:34:33 pm
content: I'd say that you've quickly found the problemI used to work on elevators and the machine room for these is normally at the top of a building, sometimes out in the open. Now imagine what happens when lightning strikes with a direct hitAt this point I wish I had kept some of the photographs, cables pushed out from plaster because of the magnetic pulse, PCBs reduced to cinders, it was a complete mess and entirely the customer's fault as they had refused to follow our recommendations for lightning protection. The funny thing is that the old elevator circuits built using BIG relays and contactors on slate beds would have probably survived.

author: SeanB
author_rank: Super Contributor
timestamp: December 22, 2017, 08:43:32 pm
content: Impressive, I guess the bridge rectifier diodes vapourised open circuit faster than the fuse could heat up to melting point, eventually. that the board itself caught fire is also impressive, and that it at least did self extinguish as well at least means there was an arc sustaining the burning, probably at the connections to that lower power switching transformer, that then created the arc that burned the board up, and created the soot and flame there.I had more expensive ones, though as they were in a hermetically sealed case there was no external flame or soot till you opened the transit case, when you could smell the volatiles that got past the seals and which were in the case packaging. Cause in all those cases was diodes going short circuit, and eventually burning out the transformer powering them, with the mains fuses often surviving the conflagration, or only blowing 2 of the 3 1A fuses eventually.

author: Gyro
author_rank: Super Contributor
timestamp: December 22, 2017, 09:01:13 pm
content: A burn-up of that magnitude on a modern piece of consumer equipment is getting into recall territory. It should at least have blown an appropriately rated fuse!EDIT: I suspect that itisa recall issue, check throught the 1 Star reviews....https://www.amazon.com/Seiki-SE39UY04-39-Inch-Ultra-Discontinued/product-reviews/B00DOPGO2G/ref=cm_cr_arp_d_paging_btm_next_2?ie=UTF8&filterByStar=one_star&reviewerType=all_reviews&pageNumber=2#reviews-filter-bar

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: December 22, 2017, 09:59:43 pm
content: Quote from: Gyro on December 22, 2017, 09:01:13 pmWow really? Thats impressively bad. Dave should get ahold of the affected model and see why it does it, though he'd need a 120v power source

author: Ampera
author_rank: Super Contributor
timestamp: December 22, 2017, 10:15:06 pm
content: Quote from: iamdarkyoshi on December 22, 2017, 09:59:43 pmI believe he has some sort of VariAC, but I could be wrong. He probably also has something even nicer than that, but, again, I don't know.

author: M4trix
author_rank: Frequent Contributor
timestamp: December 22, 2017, 10:20:28 pm
content: QuoteYeah, right.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: December 22, 2017, 10:23:06 pm
content: Quote from: M4trix on December 22, 2017, 10:20:28 pmI'll give them the impressively bad explosion award!

author: Gyro
author_rank: Super Contributor
timestamp: December 22, 2017, 10:32:39 pm
content: I liked the bit in the reviews where people were complaining that they had to ship failed units back to the company, at their own expense, in order to receive a refund. They claimed it was too expensive to supply replacements.Well I suppose thats asort ofrecall.

author: TerraHertz
author_rank: Super Contributor
timestamp: December 22, 2017, 10:33:03 pm
content: QuoteWell it probably was a very entertaining experience. Straightforward too - there's the essential jet of flame, no question about that. No money wasted on costly frills like fuses and current limit sensing. Win!

author: Cyberdragon
author_rank: Super Contributor
timestamp: December 22, 2017, 10:54:00 pm
content: Quote from: TerraHertz on December 22, 2017, 10:33:03 pmOur devices incorporate the new planned failure mode called fun failure mode. Now with less safety features making it the lowest cost possible. Our devices are guaranteed to continue to provide entertainment when they inevitably fail!

author: Ampera
author_rank: Super Contributor
timestamp: December 22, 2017, 11:22:40 pm
content: Perhaps they should go into the electric cooker business. I've heard burning fibreglass is a desirable taste in food.

author: station240
author_rank: Unknown
timestamp: December 22, 2017, 11:48:29 pm
content: Quote from: M4trix on December 22, 2017, 10:20:28 pmSounds like a new motherboard I was trying to get working, for someone.Google search revealed it won an award, in a Russian computer magazine for "best budget model" 3 years previously.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: December 23, 2017, 06:23:41 am
content: Anyone know if Dave is still doing EEVSmoke? I submitted this in case he is, I hope he gets a kick out of it

author: Red Squirrel
author_rank: Super Contributor
timestamp: December 23, 2017, 07:06:48 am
content: Wow that's quite impressive. Reminds me of this time I got a broken TV for free, it was headed to the garbage so figured I'll take it, just to see if it turns out to be something simple like a fuse.It was the fuse... but it blew for a reason. The reason, I do not quite know, because being a total noob, even more than I am now, I just bypassed it as a troubleshooting step (was not ready to order and wait) and plugged it in. It was like celebrating Canada Day and Independence Day at the same time. It took a couple days to get the smell out of my house.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: December 23, 2017, 09:21:06 am
content: The majority of electrical fires start through loose connections in relatively high current circuits, not through overloads. The loose connection begins arcing, which heats the surrounding insulation until it carbonises and becomes conductive. The process then becomes self-reinforcing.Fuses cannot protect against such incidents because there is typically no overcurrent, at least not until the burn-up is well under way.Dry jointed SMPS transformer pins are a possible place for this kind of incident, because the HF AC current is ideal for sustaining an arc, not unlike a TIG welding supply. Though, I've also seen a case where an outside floodlight PIR burned-up on the current through a 220n capacitive dropper. The cap was still OK. The board with the dry joint was not, having a massive hole in it. That's not a lot of current, but it did all that damage.An occasional cause of house fires is loose terminals in wall outlets supplying heaters. I've always thought it counterproductive that UK electricians have to fill in wads of paperwork certifying that all kinds of regulations have been complied with, when the time would be better spent checking that terminals have been properly tightened. You wonder how many fires are a direct consequence of bureaucracy being a distraction from the job.

author: amyk
author_rank: Super Contributor
timestamp: December 23, 2017, 09:43:08 am
content: My guess is that an underrated MOV caught fire due to either a slight but sustained overvoltage, or a surge on the mains.

author: capt bullshot
author_rank: Super Contributor
timestamp: December 23, 2017, 10:18:04 am
content: One can observe such failures with power electronics (like the power stage of VFDs) operating at some kWs of power. Quite unusual to see that degree of burning on a TV's power supply.

author: German_EE
author_rank: Super Contributor
timestamp: December 23, 2017, 10:47:37 am
content: One thing I don't understand, FR4, the F is for Fire and the R is for Retardant.So why does a PCB burn?

author: capt bullshot
author_rank: Super Contributor
timestamp: December 23, 2017, 12:08:38 pm
content: As long as the basic material is oxidizable it will burn at some point. The flame retardancy is just some additional stuff put into the material composition that makes it harder to set it on fire, and it will self extinguish to some extent. If you apply enough heat, it'll burn.Judging from the pictures, you see a lot of black stuff, but not really burned PCB material. The arc has surely vaporized and burned the PCB traces and some of the components, but didn't start a real fire - because of the flame retardant material.

author: Nusa
author_rank: Super Contributor
timestamp: December 23, 2017, 12:31:37 pm
content: Flame Retardant is not Flame Proof. It will burn while sufficient flame or heat is applied to it. However, FR-4 is supposed to self-extinguish within 10 seconds after the heat sources are removed (traces/wires melt) or exhausted (flammables in components).

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: December 23, 2017, 06:19:51 pm
content: The plastic insulator card from this thing probably helped with the fire...And as another user pointed out, this seemed like a somewhat common issue with this model, looking at amazon reviews

author: Zero999
author_rank: Super Contributor
timestamp: December 23, 2017, 07:44:17 pm
content: Any idea of what was on the board, where the char is?I agree that the PCB itself doesn't appear to have been much of a fuel source. I believe FR-4 is more glass, than resin, so shouldn't burn much any way. Yes, the plastic insulator card and possibly some of the components were probably the major fuel sources. What tends to happen is, heat due to excessive power consumption, causes pyrolysis of organic matter (plastics, rubbers, paper etc), releasing various toxic, flammable and explosive gasses: carbon monoxide, hydrogen, benzene and tars. If there's no source of ignition, you'll smell and see some of these gasses as a nasty agic smoke, if there's an ignition source, such as a spark or it reaches the autoignition temperature, the result will be a flame. An explosion can occur, when flammables gasses mix with air before ignition from spark or it reaching its autoignition temperature.Flame retardants can help prevent fire, but they won't stop it completely and if there's enough heat, from another source, such as a nearby fire, an arc or just Ohmic heating, they can be rendered ineffective.

author: M4trix
author_rank: Frequent Contributor
timestamp: December 23, 2017, 09:44:38 pm
content: @iamdarkyoshi,wash the board with IPA. Let's see the impact on 'ground zero'.Edit: I removed the gif. The very bright light might damage some monitors.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: December 23, 2017, 09:50:35 pm
content: Quote from: M4trix on December 23, 2017, 09:44:38 pmIts tempting. But its at work, and its christmas break, I won't be able to until like january 2ndWhat I do know is that a lot of the board is going to disappear, it burned completely through the board in places

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: December 23, 2017, 11:08:31 pm
content: Quote from: M4trix on December 23, 2017, 09:44:38 pmI always snip images when I'm quoting, keeps the thread less cluttered.